1. Cell biology (cytology)
Cell theory
Hooke (1665): described tiny square boxes of a thin slice of cork called them cells.
Leeuwenkoek (1675): described the 1st living cells.
Brown (1831): described the presence of a central body in each cell & called it the nucleus.
Schleiden (1838): showed all plants are composed of cells.
Schwaan (1839): showed all animals are composed of cells animal cell lacks cell wall that found in plant cell.
Watson & Crick (1953): developed the model of DNA which is the hereditary material.

2. Cell theory: Types of cells
It states:
1- All living organisms are made of cells.
2- The cell is the smallest living thing that can perform all the functions of life.
3- All cells must come from preexisting cells.
Types of cells
There are two basic types of cells (according to internal complexity) which are:
A- Prokaryotes:
Main characteristics of prokaryotes:
1- They are the smallest, most primitive and most diverse.
2- They are mainly unicellular.
3- They have cell walls above the cell membrane.

3. The classic example of prokaryotes is Bacteria
4- They do not have a nuclear membrane.
5- They lack membranous organelles
6- Ribosomes are slightly smaller than those found in eukaryotes.
7- They have a faster rate of division.
8- They never form tissues.
The classic example of prokaryotes is Bacteria

4. General plan of prokaryotic cell
Bacteria
* Single strand
* Circular
* Attached to cell membrane
* Attached with small amount of protein
e.g. Bacteria

5. 2- Eukaryotes The main characters of eukaryotic cells are:
* Include complex forms.
* The presence of nuclear membrane (nucleus).
The presence of membranous
organelles.
e.g. Animal and plant cells
An eukaryotic animal cell

6. Another shape of eukaryotic animal cell
An animal cell
Another shape of eukaryotic animal cell

7. Another shape of eukaryotic animal cell

8. Another shape of eukaryotic animal cell

9. An eukaryotic plant cell rough endoplasmic reticulum (ER)
Central vacuole
mitochondrion
nuclear envelope
chromatin
microtubules
nucleus
nucleolus
microfilaments
rough endoplasmic reticulum (ER)
chloroplast
smooth ER
plasmodesmata
peroxisome
ribosomes
cell wall
Golgi apparatus
plasma membrane

10. Another shape of eukaryotic plant cell

11. The difference between plant cells & animal cells where:
1- The plant cells lack centrioles which involved in
mitotic cell division.
2. Plant cells have chloroplasts (site of photosynthesis).
3- Plant cells have cell wall (composed cellulose, pectin or both of them). ???!!!!!!
4- Plant cells have large central vacuole. ???!!!!
Cell shape
Variable: oval, spindle, amoeboid, flat, polyhedral, spherical, square, columnar….etc.
Cell size
Variable: related to the function.
* The smallest is red blood cell (RBC).
* The largest is the ovum (egg) {ostrich egg = 0.5 kg , 30 cm).
* The longest is the nerve cell (1 m).

12. Organelles (organoids)
The cell
Cytoplasm
Nucleus
Organelles (organoids)
Inclusions
1- Nuclear membrane
2- Nuclear sap
Membranous org.
Non-membranous org.
3- Nucleoli
4- Chromatin network
1- Ribosomes
2- Microtubules
1- Cell membrane
3- Centrioles
1- stored food
2- Mitochondria
2- secretory granules
3- Endoplasmic reticulum
4- Golgi apparatus
3- colored pigments
5- Lysosomes
4- Crystals
6- Microbodies (peroxisomes)

13. Cytoplasmic organelles
A- Membranous organelles
1- The plasma (cell) membrane (plasmalemma):
It is very difficult to seen by light microscope ( Angstrom).
By using electron microscope, it shows three layers model
Three layers (trilamellar) model
Dark layer
Light layer

14. Molecular structure of cell membrane:
It is made of
1) Lipid component:
i- Phosopholipid molecules:
a- Heads: (phosphate groups) (hydrophilic) (polar) (charged).
b- Tails: (fatty acids) (hydrophobic) (non-polar) (non-charged).
Dark layer
Cytoplasm
Exracellular (intercellular) fluid
Light layer
Phosphate polar heads
Fatty acids non-polar tails

15. Phospholipid bilayer (Trilamellar membrane)
Hydrophillic heads (phosphate groups)
(polar)
Extracellular fluid
Hydrophobic tails
(fatty acid tails)
(non-polar)
Bilipid
layer
Phospholipid molecule
Hydrophillic heads
Cytoplasm
So, phospholipids are arranged into two layers i.e. form a bilipid layer.
Also, it is arranged in trilamellar membrane (dark, light and dark layers).

16. Molecular structure of cell membrane (continue):
ii- Cholesterol molecules:
a- Hydroxyl radicals: (hydrophilic).
b- Steroid nuclei: (hydrophobic).
Note: Cholesterol is found in the hydrophobic tails of phospholipid especially to the inner cytoplasmic ones.
2) Protein component:
i- Integral (intrinsic) protein:
a- Small molecules: embedded in the lipid bi-layer.
b- Large molecules: in the center & extended from both surfaces.
ii- Peripheral (extrinsic) protein: loosely attached to both surfaces.

17. Small molecule
Large molecule

18. 3) Carbohydrate component
It is polysaccharides. It may be attached to:
i- Protein forming glycoproteins.
ii- Phospholipid forming glycolipids.
Both glycoproteins & glycolipids are called glycocalyx (cell coat).
The following structure of plasma membrane form what is known as:
fluid-mosaic model
which states that:
The cell membrane is phospholipid bilayer with protein molecules partially or wholly embedded.
The following diagrams represent this model.

19. Plasma (cell) membrane filaments of cytoskeleton
(fluid mosaic model)
Extracellular fluid
glycoprotein
Glycocalyx
carbohydrate
protein
lipids
glycolipid
cholesterol
phospholipid
filaments of cytoskeleton
cytoplasm

21. Functions of the protein in the plasma membrane:
1) Acts as channels.
2) Acts as enzymes.
3) Acts as receptors
4) Acts as markers (cell identification markers):
5) Acts for cell adhesion:
6) Determine the ABO blood grouping (typing).

22. Functions of plasma membrane proteins
(1)
(2)
(3)
(4)
(5)
(5)

23. 1- Passive transport: Functions of the cell membrane
Different substances can pass into and out of cells at different rates is partly due to the properties of the particles and the structure of the plasma membrane.
Movement into and out of the cell happens in many different ways which are:
1- Passive transport:
The cell membrane is referred to as selective permeable (semi-permeable).
1) It does not require energy. It is achieved by the kinetic energy of the molecules.
2) It takes place according to (= with) the concentration gradient.
It continues until the concentration of the molecules is the same on both sides of a membrane i.e. equilibrium.

24. The passive transport comprises:
a) Simple diffusion:
It transports solutes such as O2, CO2, peptides, cholesterol and small hydrophobic molecules (i.e. non-polar solutes).
Note: A polar solute cannot pass through the membrane because it cannot pass through the non-polar lipid core of the membrane.
The rate of diffusion depends on temperature and size.
Molecules diffuse faster at higher temperatures.
Smaller molecules diffuse faster.

25. b) Facilitated diffusion:
It transports solutes such as Glucose.
It is facilitated because a transport protein in the membrane enhances (increases) the transport of the substance across the membrane.
It take place through pores and gated channels.
Inside the cell
Outside the cell
A transport protein
Inside the cell
Outside the cell
Low
concentration
of solutes
High
concentration
of solutes

26. Two models for facilitated diffusion
(A) pores
(B) gated channels

27. c) Osmosis:
It is the diffusion of water (solvent) from an area of high water concentration (hypotonic solution) (less solute) to an area of lower water concentration (hypertonic solution) (more solute) .
i.e. The transport is achieved according to the concentration gradient i.e. from higher water concentration to lower concentration (of water).
Also, it needs no energy.

28. Osmotic relationships in cells:
When the cell is placed in:
1) A hypertonic solution
Water diffuses out of the cell till equilibrium is reached.
It will shrink and die.
This condition is called plasmolysis.
2) A hypotonic solution
Water diffuses into the cell till equilibrium is reached.
It causes it to swell and often burst.
This condition is called cytolysis.
3) An isotonic solution

29. 2- Active transport:
It takes place against the concentration gradient.
It uses energy (in the form of ATP).
Also, it uses membrane proteins.
An example of this type of active transport is the sodium-potassium pump.
The sodium-potassium pump is formed from:
1) Carrier proteins; each has 3 receptor sites for Na+ (inside of the cell) and 2 receptor sites for K+ (on the outside).
2) Adenosine triphosphatase (ATPase) (enzyme) adjacent (near) to the Na+ binding sites.
3) ATP that pumps Na+ out of the cell and K+ into the cell.

30. Mechanism of sodium-potassium pump:

32. So, an electrical gradient across the cell membrane was achieved i. e
So, an electrical gradient across the cell membrane was achieved i.e. the outside of the membrane becomes positively charged and the inside of the membrane becomes negatively charged.
This unbalanced charge is important for conduction of nerve impulses, muscle contraction, … etc.

33. Summary +
H2O Osmosis
Simple

34. It needs energy like active transport.
3- Bulk transport (vesicle-mediated transport) (endocytosis & exocytosis):
It needs energy like active transport.
It transports large molecules through vesicles.
It comprises:
a) Endocytosis:
It moves large molecules into the cell.
It includes three different processes which are:
i- Phagocytosis
i- Phagocytosis (cell eating):
When the formed vesicle encloses solid food particles (such as bacteria, damaged cells, large food particles or whole cells) with little extracellular fluid.

35. ii- Pinocytosis (cell drinking):
When the formed vesicle encloses mainly extrcellular fluid i.e. liquid
iii- Receptor-mediated endocytosis:
When specific molecules - such as microbes - in the extracellular fluid bind to sites on the plasma membrane.
Note
Endocytosis removes membranes from cell surface to form vesicles.
ii- Pinocytosis
iii- Receptor-mediated endocytosis

36. Summary
Endocytosis

37. b) Exocytosis
It is applied when the transportation is out of the cell.
It transports secretory products such as mucous and enzymes or waste products made in the cell.
Note
Exocytosis adds membranes to the cell surface form vesicles.
Exocytosis

38. 2- Mitochondria Mitochondrial structure:
It is found in all nucleated cells, (absent in RBCs).
Mitochondrial structure:
They are bounded by a double membrane; smooth outer membrane and folded inner membrane.
The folds of the inner membrane is called cristae that increase the inner membrane’s surface.
The distance between both membranes is called inter membrane space.
The matrix contains DNA (found in the nucleus), ribosome (found in the cytoplasm), granules and ATP synthase particles.

39. 2- Mitochondria (continue)
Notes
The mitochondria are found in a great number in the cells with high activity e.g. muscle and liver cells.
The number of cristae depends on the activity of the cell. i.e. The cell with high activity has numerous close cristae.
الخلاصة أن الميتوكوندريا ثشبه النواة فى:
(1) أنها تحاط بغشائين.
(2) أنها تحتوى على الــ (DNA) الموجود فى النواة والذى يكون الجينات المكونة للكرموزومات.
** أما الريبوسومات (Ribosomes) فتوجد فى السيتوبلازم.
It is responsible for formation of energy (ATP) from nutrients, hence they are called the powerhouse of the cell.
ATP is required in different vital activities such as muscle contraction, protein synthesis, active transport, …etc.

40. 3- Endoplasmic reticulum (ER)
ER occurs in all kinds of nucleated cells.
It a system of hollow network of branched and joined tubules .
Note: 1 1 cm3 (mL) of liver tissue contains about 11 m2 of ER.
There are 2 types of ER which are:
1) Rough (granular) ER which covered by ribosomes.
2) Smooth (agranular) ER which lacks ribosomes.

41. 3- Endoplasmic reticulum (ER) (continue)
Note
Both types may be connected in the same cell.
Also, one type may be changed to the other depending on the need of the cell.
Functions of ER:
1- Helps molecules to transport through the cell and from one cell to another (both rough & mooth ER).
2- Involved in the synthesis of proteins due to the presence of ribosomes (rough ER).
3- Involved in the synthesis of steroids (smooth ER).
4- Helps to regulate calcium levels in muscle cells (smooth ER).
5- Helps in the break down of toxic substances in the cell (smooth ER).

42. 4- Golgi apparatus (Golgi body) (Golgi complex)
It was found in eukaryotic cells.
The Golgi apparatus is made up of:
ER & Nucleus
1- A stack of flattened elongated sacs called cisternae.
The cristernae have:
i) A cis (immature) face {directed towards the ER and nucleus},
Plasma membrane
ii) The medial region {in the middle} and
iii) The trans (mature) face {directed towards the plasma membrane}.

43. 4- Golgi apparatus (Golgi body) (Golgi complex) {continue)
2- Vesicles: Which may be:
a) Incoming transport vesicles (microvesicles) (transferring vesicles) which are detached from rough ER. They move towards the cis-face of cisternae. These vesicles contain the newly synthesized protein.
b) Outgoing transport vesicles (large vesicles) which are detached from the trans face of cisternae. These vesicles are filled with protein.
c) Intermediate vesicles which are found in large number close to the periphery of the medial region of sacs 9 cisternae).

44. Functions of Golgi apparatus:
1) Storge: Proteins that formed by ribosomes migrate as incoming transport vesicles (microvesicles) to fuse with the membrane of cis-face where they are collected, condensed and then enclosed by membranes forming outgoing transport vesicles (large vesicles) that contain secretory granules. These vesicles move to the plasma membrane where they release their contents by exocytosis.
2) Packing: It forms lipoproteins by bounding both lipids (from smooth ER) and proteins (from rough ER) inside a membrane. The formed lipoprotein granules release from trans-face of Golgi apparatus.
3) Secretion: Such as hormones (by endocrine glands), enzymes (by exocrine glands), mucous (by goblet cells).
4) It helps in the formation of the acrosome of the sperm which has the ability to penetrate the membrane of the ovum

45. Functions of lysosomes:
They are saclike structure surrounded by a single membrane. It contains powerful digesting enzymes such as acid phosphatase, deoxyribonuclease, ribonuclease, … etc.
Their number is affected by different physiological and pathological changes.
Decrease their number during fasting and ageing.
Functions of lysosomes:
Lysosomes are responsible for digestion of biological compounds.
This digestion may be one of the following:
i) Intracellular digestion: This takes place inside the cytoplasm which may be:

46. a) Exogenic origin: They digest the taken substances by endocytosis in a process known as heterophagy. The engulfed material is then digested by the enzymes into small molecules.
b) Endogenic origin: They digest some part of the cytoplasm e.g. mitochondria by a process known as autophagy.
Heterophagy
Autophagy
??!!!
Note
If digestion is completed, residual bodies may be formed which may be go out by exocytosis or may be remain in the cell.
These remaining residuals represent an index of cell ageing.

47. ii) Extracellular digestion:
Lysosomal enzymes discharge (= go) outside the cell to destroy some surrounding structures.
This explains how the sperm can penetrate the protecting coat of the ovum during fertilization.
iii) Autolysis:
It is a process in which the cell is self-destructed.
When cells approach death, lysosomes rupture in the surrounding cytoplasm causing the digestion of the whole cell.
This action is not accidental but it is regulated by signals that scientists do not fully understand.

48. 6- Peroxisomes (microbodies)
They are about the same size, or slightly larger than lysosomes.
They contain enzymes such as that involved in the degradation of fatty acids and amino acids and catalase.
Peroxisome function:
Peroxisomes contain enzymes that degrade fatty acids and amino acids.
In doing so they produce hydrogen peroxide (H2O2).
H2O2 is very toxic because it is unstable and spontaneously degrades to produce compounds called free radicals.
Free radicals are very reactive because they have unpaired electrons and will react with a variety of cellular macromolecules and alter their structure.
Fortunately peroxisomes contain the enzyme called catalase that degrades hydrogen peroxide to the less dangerous oxygen and water.
catalase
H2O2
O (H2O)

49. B- Non-membranous organelles
1- Ribosomes
They are found in both prokaryotes and eukaryotes but they are larger in eukaryotes.
They are formed in the nucleolus then pass through the nuclear pores to the cytoplasm.
Each ribosome is composed of 2 subunits, a small subunit and a large subunit. Between them there is a small cleft in which a central growing polypeptide chain is present.
Chemically, they are consisted of * ribosomal RNA (rRNA) (65%) and * proteins (35%) i.e. ribonucleoprotein.
Ribosomes are found in 3 different places or cases in cells which are:
1. Free floating in cytoplasm as individual subunits or dimers.
2. Membrane bound on outer surface of rough ER.
3. Attached to mRNA molecule in a polysome (polyribosome).

50. Function of ribosomes:
Ribosomes are the site of protein synthesis.
The mechanism
They receive amino acids (the building units of protein), grouping them into peptide chains by interaction between transfer RNA (tRNA) which carries the amino acids and messenger RNA (mRNA) which carries the specific genetic code from DNA in the nucleus.

55. 2- Microtubules
The microtubule is a long cylindrical structure with a cavity. It is elastic and capable to bend without breaking.
Chemically, it is made of dimmers of alpha and beta tubulin (a type of protein).

56. Functions of microtubules:
1- Microtubules form centrioles, cilia, flagella and microvilli.
2- They facilitate the transport of various particles inside the cytoplasm.
3- They share in the formation of cytoskeleton of the cell.
Note
The cytoskeleton determines the shape and provides mechanical support to the cell.
It is formed from:
1) Microfilaments,
2) Intermediate filaments and
3) Microtubules.

57. 3- Centrioles
Centrioles are short hollow cylindrical tubules that found near the nucleus.
There are two centrioles at right angles to each other Centrosome
Each centriole consists of 9 peripheral sets of microtubules arranged in a pin-wheel of 3 microtubules (triplet) in each set.
Thus, each centriole consists of 27 (3x9) microtubules in the configuration of (9+0).
Functions of centrioles:
1- They play an important role in the process of cell division where they form spindle fibers.
2- They are able to replicate giving identical structures that migrate towards the plasma membrane to form basal bodies from which cilia or flagella.
3- They are involved in the cytoplasmic movement.

58. The 9+2 arrangement of microtubules in a flagellum or cilium.
Basal bodies:
So, the basal bodies and centrioles are homologous structures with the same configuration (9+0). Each cilium or flagellum has a basal body located at the base.
Flagella and cilia:
Cilia and flagella are hair-like structures projecting from the basal bodies (that found in the cytoplasm) and enclosed (covered) by the plasma membrane.
Eukaryotes have 9 doublets (pairs) of microtubules arranged in a circle around 2 central microtubules i.e. (9 + 2).
The 9+2 arrangement of microtubules in a flagellum or cilium.
Cilia are being much shorter than cilia.
Many unicellular organisms such as Paramecium move by cilia.
Many unicellular organisms such as Euglena move by flagella.

59. The upper respiratory tract have cilia while sperms use flagella to move.
Microvilli
They are formed from microtubules covered by cell membrane.
They are finger like structures projecting from the surfaces of some cells of intestine or kidney.
They increase the surface area for absorption.

60. Nucleus The nucleus occurs only in eukaryotes.
It has a role in controlling the shape and features of the cell.
When a cell has grown to a certain size it divides into two cells.
Nuclear sap
It is composed of:
1- Nuclear membrane
(nuclear envelope),
2- Nuclear sap,
3- Nucleolus and
4- Chromatin network.

61. Structure of the nuclear envelope and nuclear pores
1- The nuclear membrane (envelope)
It appears as a double membrane (outer and inner); each is similar in structure to the plasma membrane.
Structure of the nuclear envelope and nuclear pores
Numerous nuclear pores occur on it, allowing RNA and other chemicals to pass while DNA can not go out through it.
Functions:
It was used to protect DNA (genetic material that found in the nucleus forming the chromosomes) from reactions that occur in the cytoplasm which could damage it.
2- The nuclear sap (nucleoplasm):
It is a colloidal clear medium in which all the contents of the nucleus are embedded
It contains lipoproteins, ions, enzymes … etc.

62. 3- Nucleolus 4- Chromatin network:
There are one or more nucleoli in each nucleus.
It is involved in the formation of ribosomal RNA (rRNA), which is responsible for protein synthesis in ribosomes.
4- Chromatin network:
The material of chromatin network is formed mainly from DNA as a double helix around a core of protein called histone.
DNA form the genes of chromosomes.
Chromatin network is found in two forms which are:
1- Euchromatin (active chromatin) (extended chromatin):
They found in active cells.
They appear as thin threads.
They are involved in protein synthesis.
2- Heterochromatin (inactive chromatin) (condensed chromatin):
They are not involved in protein synthesis.

63. Heterochromatin appears as:
1- Peripheral chromatin:
when they are attached to the inner nuclear membrane (nuclear envelope).
2- Chromatin islands:
when they are scattered as granules in the nuclear sap.
Functions of chromatin network:
1) It carries genetic information.
2) It directs protein synthesis by coding the DNA bases to form mRNA.

64. The nitrogenous bases of DNA & RNA
Nucleic acids
They include DNA and RNA.
A nucleotide
They are composed of repeated units called nucleotides.
Each nucleotide is composed of:
1- A nitrogenous base,
2- A pentose sugar and
3- A phosphate group.
The nitrogenous base may be:
i- Pyrimidines: They include:
Cytosine (C), Thymine (T) and Uracil (U).
The nitrogenous bases of DNA & RNA
i) Pyrimidine
ii) Purine
ii- Purines: They comprise:
Adenine (A) and Guanine (G).

65. Both DNA and RNA contain adenine and guanine (purine bases) and cytosine (pyrimidine bases).
Thymine is found in DNA while uracil is found in RNA.
There are two major pentoses in nucleic acids: deoxyribose in DNA and ribose in RNA.
The phosphate group is found in the nucleotide of both DNA and RNA.
Nucleotides are linked together in both DNA and RNA via covalent bonds that found between phosphate group and pentose sugar.
Nitrogenous bases (purine or pyrimidine) are joined by glycosidic bonds to pentose sugar of a repeating sugar-phosphate backbone.
RNA is usually a single-stranded, whereas DNA is usually a double-stranded helix.
In DNA, the nitrogenous bases of the two strands are connected together via hydrogen bonds.
Adenine binds to thymine through two hydrogen bonds while cytosine binds to guanine by three hydrogen bonds.
The sequence of a nucleic acid is usually read from 5' (the end that has the phosphate group) to 3' (the end which has not phosphate group).
The two strands of DNA run in opposite directions i.e. 5' end of one strand is opposite 3' end of the other strand.

68. 3 Nucleotides A single strand of DNA A single strand of RNA
A double strand of DNA
3 Nucleotides

69. Triplet sequence in DNA
DNA is found mainly in the nucleus. Very small amount is found in the mitochodria.
RNA is formed in the nucleus and pass to the cytoplasm carrying informations about the structure of protein which will synthesized in the ribosomes.
There are different types of RNA; the most famous of them are messenger RNA (mRNA), transfer RNA (tRNA) and ribosomal RNA (rRNA).
Notes
Genes
Enzymes
Metabolism
DNA
Transcription
Translation
RNA
Protein
DNA sequence
RNA sequence
amino acid sequence
Triplet sequence in DNA
(TAC)
Codon in mRNA
(AUG)
Amino acid in protein
(Met.)

70. Replication is the copying of DNA into DNA.
Transcription is the copying of DNA sequence into RNA.
Translation is the copying of RNA sequence into protein.

71. Triplet sequence in DNA is the genetic word called codon i. e
Triplet sequence in DNA is the genetic word called codon i.e. 3 nucleotides equal to 1 codon which again equal to 1 amino acid.
The Size of human genome is ≈ 3,000,000,000 base pairs ≈ 500,000,000 possible codons (words or amino acids).
Humans, mice and indeed all mammals have roughly the same number of nucleotides in their genomes (about 3 billion base pairs). 

72. CYTOGENETICS Cell division
Cell division in prokaryotes
Prokaryotes such as bacteria use a relatively simple form of cell division called binary fission.
Typically bacterial chromosomes consist of a single loop of DNA often called circular DNA but eukaryotes have a linear DNA molecule.
When the prokaryote reaches to a level to be dividing, the circular chromosome attaches to the cell membrane at a certain point.
Bacterial chromosome replicates leading to two identical chromosomes which are attached to separate points.
The cell begins to divide giving two daughter cells which are identical to the parent cell.
Bacteria can divide every minutes.
This gives bacteria a remarkable power of multiplication where each cell gives 2.81 x 1014 bacteria after one day.

73. Cell division in eukaryotes
There are two types of cell divisions which are mitosis and meiosis.
The cell cycle
There are two main stages in the cell cycle:
I) Interphase:
It is the part of the cell cycle when the cell is doing its normal job.
Generally, there are one or more nucleoli in each cell which are the sites of ribosomal RNA synthesis.
Interphase has three big phases which are:
1) G1 phase
◙ In this phase, the cell is doing its normal (everyday) job.
◙ ◙ At this time, chromosome (2n) are called unduplicated or unreplicated chromosomes.
$ Usually, G1 is the longest period of the cell cycle.
$ However, in some embryonic cells that are rapidly divided, G1 might only last a few minutes i.e. very short.
$ Some cells, like nerve cells never leave G1 and this is sometimes called a G0 state (phase).
$ G1 prepares the cell to undergo the next stage (S phase).

75. 2) S phase
◙ All chromosomes are duplicated where DNA is replicated.
◙ ◙ New proteins are synthesized to assemble with new DNA forming new chromosomes.
The time necessary to complete S phase varies between different life stages and between species.
During S phase, the entire cell's DNA is duplicated resulting in 4 copies of each gene instead of the normal 2 in a diploid cell.
3) G2 phase
◙ Cell prepares itself for mitosis by synthesizing needed components.
◙ ◙ Some cells remain in interphase (G1 + S + G2) their whole life because they do not divide e.g. nerve cells and adult muscle cells.
The result of cell cycle is the cell proliferation (division) while any uncontrolled proliferation leads to cancer.
Notes
☼ Cells spend most of their time in this intermediate non-mitotic state (interphase).
☼ ☼ Interphase is not a part of mitosis but it is stage between two successive mitotic divisions.

76. II) Mitosis: 1- Prophase It takes place in somatic cells.
It is an asexual reproduction for grow and replace damaged cells.
It is differentiated into the following phases (stages):.
1- Prophase
@ Chromatin begins to coil and condense to form chromosomes which become visible.
@ The nuclear membranes disappear.
@ The nucleolus or nucleoli have disappeared.
Paired centrioles (centrosomes) move to opposite ends of the cell.
As they move apart, the mitotic spindle are formed.
The mitotic spindle consists of:
1) The asters which radiate in a star like pattern away from each centrosome, and
2) The spindle fibers which go toward the equator of the cell.

77. 2- Metaphase
Spindle fibers grow and form attachments to the chromosomes at the centromeres.
Chromosomes move to an equatorial plate (metaphase plate) which is formed along the midline of the cell between the poles.
Chromosomes are found in the most condensed state.
Remember that the chromosomes are still duplicated during metaphase.
3- Anaphase
Centromeres are divided leading to the formation of daughter chromosomes.
Spindle fibers shorten and the daughter (sister) chromosomes are drawn to the opposite poles of the cell.

78. Cytokinesis (division of the cytoplasm):
4- Telophase
Nuclear membrane (envelope) is reformed (reassembled) and surrounds each set of daughter chromosomes.
Nucleolus or nucleoli reappear inside the newly formed nucleus.
Remember that the chromosomes are still duplicated during metaphase
Chromosomes are decondensed in the daughter cells to become chromatin and the cells are once again in interphase.
Cytokinesis (division of the cytoplasm):
It is the division of the cytoplasm.
The result of mitosis plus cytokinesis is typically two genetically identical daughter cells.
Both daughter cells are smaller than the original parent cell and have unduplicated chromosomes.

80. Prometaphase
Prophase
Interphase
Metaphase
Anaphase
Telophase

81. Meiosis:
Meiosis is the process by which haploid cells are produced from diploid cells.
Meiosis has several functions:
@ Reduce the chromosome number from the diploid number (2n) to the haploid number (n).
@ This guarantees the male and female gametes share in the hereditary characters of the formed zygote in sexual reproduction.

82. Prophase I
Meiosis I
Metaphase I
Anaphase I
Telophase I
Meiosis II
Prophase II
Metaphase II
Binary fission
Telophase II
Telophase II

83. Comparison between mitosis & meiosis Crossing over takes place.
It is an indirect division.
It is a reduction division.
It occurs in somatic cells.
It occurs in germ cells of gonads (testes or ovaries).
Two daughter cells are produced with
diploid number of chromosomes (2n).
Four daughter cells are produced with
haploid number of chromosomes (n).
No crossing over takes place.
Crossing over takes place.

84. Gametogenesis (creation of gametes)
The formation of sperms in the testes is called spermatogenesis.
The formation of eggs (ova) in the ovaries is called oogenesis.
Gametogenesis includes three successive phases which are:
I- Multiplication phase,
II- Growth phase and
III- Maturation phase.
Spermatogenesis
Oogenesis
Primordial germ cell 2n 2n
I- Multiplication phase
By repeated mitotic cell division
(i.e. by mitosis) 2n 2n 2n
Spermatogonium
Oogonium 2n
II- Growth phase
By growing
1ry spermatocyte 2n
1ry oocyte 2n
2ry spermatocyte
1st polar
body
2ry oocyte
1st meiotic division
1st meiotic division n
III- Maturation phase
By meiosis n
2nd meiotic division
2nd meiotic division n
Spermatid n n
Spermatozoon
Mature ovum
2nd polar body
2 polar bodies

85. So, each primary spermatocyte (or spermatogonium) gives four sperms.
Also, each primary oocyte (or oogonium) gives one ovum (egg) and three polar bodies.
The formed three polar bodies are degenerated (disintegrated).
At puberty, a male will produce approximately 1000 sperm per second .
Mature human sperm
Tail
Neck
Each ejaculation should contain million sperms.
When the sperms are formed, they are moved into the epididymis where they become mature then stored.
From puberty of a female to menopause, one egg is normally formed per month.
Fertilization
It the fusion of two haploid gametes (sperm and egg) to produce a diploid zygote.

86. Sequence of fertilization
1- The acrosomes of thousands of sperms release their enzymes that destroy the protective barrier (a gelatinous material) around the ovum and clear a pathway (is called fertilization pathway) for other sperms to follow.
2- At the point of contact between the sperms and the ovum, the egg surface produces a conical projection known as the entrance.
3- Although thousands of sperms work to clear the fertilization pathway, only one sperm actually enters the ovum. This successful sperm binds with a receptor on the cell membrane of the ovum. So, the successful sperm is engulfed and enter the ovum..
4- A biochemical changes occur that inhibit other sperms from penetration.
5- A change in the surface layer of the egg that preventing the entrance of other sperms.
Note:
During fertilization, the head and the middle piece (midpiece) of the sperm pass into the cytoplasm of the ovum while the tail is cut off and remains outside.

87. Embryonic development
The embryonic development of any animal starts from the fertilized egg (zygote) which usually passes through three main stages which are:
1) Cleavage, 2) Gastrulation and 3) Organ formation (organogenesis).
1) Cleavage:
After fertilization, the zygote divides repeatedly by a series of mitotic divisions.
vertical
Zygote
2-blastomere stage
at right angle to the
1st division
horizontal
4-blastomere stage
double vertical
16-blastomere stage
8-blastomere stage
double horizontal
32-blastomere stage (morula)
64-blastomere stage
128-blastomere stage
A blastula

88. The blastula
@ It is a hollow structure formed at the end of cleavage process.
@ Its wall is consisted of a single layer of cells.
These cells are differentiated into micromeres at the animal pole and macromeres at the vegetal pole.
@ The fluid filled cavity in its center is termed blastocoel.
This blastocoel is not connected to the exterior.

89. 2) Gastrulation: The gastrula
@ It is an elongated structure formed at the end of gastrulation by flattening and invagination of macromeres of blastula.
Invagination continues until the macromeres come in direct contact with micromeres.
So, the blastocoel is disappeared while a new cavity (archenteron) is formed.
@ Its wall is formed from a double layers of cells.
The outer layer which is formed from micromeres (is known as the ectoderm) while the inner layer is formed from the macromeres (the endoderm forms).
@ It has a cavity that called archenteron which is connected to the exterior through an opening called a blastopore.

90. مع أرق تحياتى وأمنياتى لكم جميعا بالتوفيق والتفوق ا. د
مع أرق تحياتى وأمنياتى لكم جميعا بالتوفيق والتفوق ا.د. شــــبل شــــعلان