1. The Cellular level of Organization
Chapter 3
The Cellular level of Organization
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2. Cell Day!

3. Study of Cell Functions
Cell biologists can isolate organelles to study their functions
The goal of cell fractionation is to separate the major organelles of the cells so that their individual functions can be studied.

4. Fractionation begins with homogenization, gently disrupting the cell.
This process is driven by a ultracentrifuge, a machine that can spin at up to 130,000 revolutions per minute and apply forces more than 1 million times gravity (1,000,000 g).
Fractionation begins with homogenization, gently disrupting the cell.
Then, the homogenate is spun in a centrifuge to separate heavier pieces into the pellet while lighter particles remain in the supernatant.
As the process is repeated at higher speeds and longer durations, smaller and smaller organelles can be collected in subsequent pellets.

5. Cell Structure and Function

6. Cell Characteristics Plasma Membrane Cytoplasm Organelles
Outer cell boundary
Cytoplasm
Cytosol
Cytoskeleton
Cytoplasmic inclusions
Organelles
Specialized structures that perform specific functions

7. Functions of the Cell Basic unit of life Protection and support
Movement
Communication
Cell metabolism and energy release
Inheritance

9. Plasma Membrane Intracellular versus extracellular Membrane potential
Glycolipids and glycoproteins
Fluid-mosaic model

10. Membrane Lipids Phospholipids form a lipid bilayer
Hydrophilic (water-loving) polar heads
Hydrophobic (water-fearing) nonpolar heads
Cholesterol: Determines fluid nature of membrane

11. Membrane Proteins Integral or intrinsic Peripheral or extrinsic
Extend from one surface to the other
Peripheral or extrinsic
Attached to either the inner or outer surfaces of the lipid bilayer

12. Marker Molecules
Allow cells to identify one another or other molecules
Glycoproteins
Glycolipids
Examples:
Immune system
Recognition of oocyte by sperm cell

13. Channel Proteins Nongated ion channels Ligand gated ion channel
Always open
Ligand gated ion channel
Open in response to small molecules that bind to proteins or glycoproteins
Voltage-gated ion channel
Open when there is a change in charge across the plasma membrane

14. Receptors Receptor molecules Linked to channel proteins
Exposed receptor site
Linked to channel proteins
Acetylcholine
Linked to G proteins
Alter activity on inner surface of plasma membrane

15. Enzymes and Carrier Proteins

16. Movement through the Plasma Membrane
Diffusion
Osmosis
Filtration
Mediated transport mechanisms
Facilitated diffusion
Active transport
Secondary active transport

17. Diffusion
Movement of solutes from an area of higher concentration to lower concentration in solution
Concentration or density gradient
Difference between two points
Viscosity
How easily a liquid flows

18. Diffusion

19. Osmosis
Diffusion of water (solvent) across a selectively permeable membrane
Important because large volume changes caused by water movement disrupt normal cell function
Cell shrinkage or swelling
Isotonic: cell neither shrinks nor swells
Hypertonic: cell shrinks (crenation)
Hypotonic: cell swells (lysis)

20. Osmosis

21. Osmosis

22. Filtration Works like a sieve
Depends on pressure difference on either side of partition
Moves from side of greater pressure to lower
Example: In kidneys in urine formation

23. Mediated Transport Mechanisms
Involve carrier proteins
Characteristics
Specificity
To a single type of molecule
Competition
Saturation
Rate of transport limited to number of available carrier proteins

24. Saturation of a Carrier Protein

25. Mediated Transport Mechanisms
Facilitated diffusion
Higher to lower concentration without metabolic energy
Active transport
Requires ATP
Secondary active transport
Ions or molecules move in same (symport) or different direction (antiport)

26. Secondary Active Transport

27. Endocytosis Internalization of substances by formation of a vesicle
Types
Phagocytosis
Pinocytosis
Receptor-mediated endocytosis

28. Pinocytosis and Receptor-Mediated Endocytosis

29. Exocytosis Accumulated vesicle secretions expelled from cell Examples
Secretion of digestive enzymes by pancreas
Secretion of mucus by salivary glands
Secretion of milk by mammary glands

30. Cytoplasm Cellular material outside nucleus but inside plasma membrane
Cytosol: Fluid portion
Cytoskeleton: Supports the cell
Microtubules
Microfilaments
Intermediate filaments
Cytoplasmic inclusions

31. Organelles Small specialized structures for particular functions
Most have membranes that separates interior of organelles from cytoplasm
Related to specific structure and function of the cell

32. Centrioles In specialized zone near nucleus: Centrosome
Each unit consists of microtubules
Before cell division, centrioles divide, move to ends of cell and become spindle fibers

33. Cilia Appendages projecting from cell surfaces Capable of movement
Moves materials over the cell surface

34. Flagella Similar to cilia but longer Usually only one exists per cell
Move the cell itself in wavelike fashion
Example: Sperm cell

35. Microvilli Extension of plasma membrane Increase the cell surface
Normally many on each cell
One tenth to one twentieth size of cilia
Do not move

36. Ribosomes Sites of protein synthesis
Composed of a large and small subunit
Types
Free
Attached to endoplasmic reticulum

37. Endoplasmic Reticulum
Types
Rough
Attached ribosomes
Proteins produced and modified
Smooth
Not attached ribosomes
Manufacture lipids
Cisternae: Interior spaces isolated from rest of cytoplasm

38. Golgi Apparatus
Modification, packaging, distribution of proteins and lipids for secretion or internal use
Flattened membrane sacs stacked on each other

39. Function of Golgi Apparatus

40. Action of Lysosomes

41. Peroxisomes and Proteasomes
Smaller than lysosomes
Contain enzymes to break down fatty and amino acids
Hydrogen peroxide is a by-product of breakdown
Proteasomes
Consist of large protein complexes
Include several enzymes that break down and recycle proteins in cell

42. Mitochondria Provide energy for cell Major site of ATP synthesis
Membranes
Cristae: Infoldings of inner membrane
Matrix: Substance located in space formed by inner membrane

43. Nucleus DNA dispersed throughout Consists of :
Nuclear envelope: Separates nucleus from cytoplasm and regulates movement of materials in and out
Chromatin: Condenses to form chromosomes during cell division
Nucleolus: Assembly site of large and small ribosomal units

44. Chromosome Structure

45. Overview of Cell Metabolism

46. Overview of Protein Synthesis

47. Overview of Protein Synthesis
Transcription
Copies DNA to form mRNA
tRNA carries amino acids to ribosome
Translation
Synthesis of a protein at ribosome

48. Translation

49. The cell cycle
“Omnis cellular e cellular”
Every cell forms from existing cell: where a cell forms there must be a preexisting cell
Cell cycle is the sequence of growth and division of cells
Cell divide in order to reproduce: production of offspring
Cell division functions in
Growth
structural changes
increase living material in the organism
Repair and renewal : replacing cells that die from normal wear and tear or accident
Cell division enables sexually reproducing organisms to develop from a single cell
Fertilized egg or zygote

50. Human somatic (Body cells) contain 46 chromosomes
Cell division involves the distribution of identical genetic information DNA to two daughter cells
Cell cycle involves two general periods
Interphase: At this phase, the chromosomes are duplicated in preparation for the period of cell division
Mitosis: the period of division, the nucleus and it’s cytoplasm divide to form two daughter cells
The process of nucleus division followed by division of the cytoplasm when chromosome are distributed equally to daughter cells is known as MITOSIS
Human somatic (Body cells) contain 46 chromosomes
This is the Diploid or 2N
Reproductive (sex) cells or Gamete (sperm and egg cells) have half as many chromosomes as the somatic cells i.e.. 23
This is the haploid or N

51. Mitosis produces two daughter cells
Each daughter cell has a diploid (2N number of chromosomes (in pair and look alike)
Mother cell: the cell that divides
Daughter cells: the cells that resulted from the division
In mitosis the daughter cell contain the number of chromosome as the mother cell
duplication of a mother cell chromosome results in a pair of chromatid
The two chromatids are held together at the center by the contromere
INTRPHASE
The non dividing stage of cell
The period between cell division
increase in cell size
duplication to produce chromatid pair

52. Cell Life Cycle Interphase Mitosis Cytokinesis
Phase between cell divisions
Mitosis
Prophase
Metaphase
Anaphase
Telophase
Cytokinesis
Division of cell cytoplasm

53. PROPHASE METAPHASE First visible phase of division
The chromatin material shortens and thicken
Pair of centriols begin to move towards the opposite pole
Spindle fiber appear between the separating centriols
Nuclear membrane and nucleus disappear
METAPHASE
Spindle fully formed and stretches between the centrioles at the poles
Each chromatid pair is attached to the spindle fiber by the contromere
Contromeres line up at the middle of the (equator) of the spindle
Methphase is characterized by a fully formed spindle with the chromatid pair arranged across the center

54. ANAPHASE TELOPHASE BINARY FISSION
The centromeres divide and the chromatids of each pair separate and migrate towards the opposite pole
TELOPHASE
This phase is characterized by the disappearance of the mitotic apparatus and the reappearance of formed nuclei
Two nucleus instead of one nucleus appear, one for each daughter cell
The cytoplasm divide by pinching in of opposite sides (in-furrowing) of the membrane
Daughter cells with complete cell membrane enclosing it
BINARY FISSION
Asexual reproduction in which the cell divides into two equal parts
This is the method of cell division used by the prokaryotes (bacteria) and some other unicellular organisms

55. The process of binary fission involves
Copy of single chromosome
copies of chromosome attached to plasma membrane
Growth and separation
Partition forms between the newly formed cells

56. Mitosis

57. Mitosis

58. Meiosis

59. Comparison of Mitosis and Meiosis
Property
Mitosis
Meiosis
Time of DNA replication
Occurs during Interphase before mitosis begins
Occurs during Interphase before meiosis begins
Number of division
One including PMAT
Two, each including PMAT
Number of cells
Two, each diploid (2n) and genetically identical to the parent cell
Four, gametes are each different from the parent and from each other, haploid number (n) of chromosome, in males 4 gametes (sperm cells) in females, one gamete and 3 polar bodies
Synapsis
Does not occur
During prophase 1, tetrads and crossing over
Functions
New cells are formed during growth or tissue repair; new cells have identical DNA and can perform the same function as the parent cell
Gametes are produced for reproduction; during fertilization the chromosome from the haploid gamete unite to restore the diploid number in somatic cells, increase genetic variability as a result of crossing over

60. Cellular Aspects of Aging
Cellular clock
Death genes
DNA damage
Free radicals
Mitochondrial damage