1. Chapter 3 Cell structure Cell membrane Endocytosis and Exocytosis
Cytoplasm
Cell Organelles:- Lysosom, Mitochondria, Endoplasmic reticulum, Golgi Apparatus, cell Nucleus
DNA, RNA
Protein Synthesis and Secretion

2. THE CELL Nucleus Endoplasmic Reticulum Cytoplasm Lysosomes Golgi
Apparatus
Mitochondria
Cell membrane

3. Cell and its Composition
Normally cells are composed of:
1- Water = %
2- Proteins = %
3. Lipids = 2%
4. Carbohydrates = 1%
5. Various ions = small quantities
(K+, Mg++, Phosphate
Sulphate, Bicarbonate,
Na+, Cl-, Ca++)

4. The Cell
There are many different types of cells in the body. Cells differ according to their structure and function.
A cell can be divided into 3 principal parts:
1- Cell membrane: permeable membrane surrounding the cell. It separates intracellular from extracellular environment.
2- Cytoplasm and Organelles: Cytoplasm is fluid-jelly like content of the cell in which the organelles float.
3- Nucleus: spheric body in the cell which contains genetic material. It is the commanding center of the cell.

5. Cell Membrane Extracellular Intracellular
Cell membrane forms a barrier between intracellular fluid (ICF) and extracellular fluid (ECF). It is composed of phospholipids, proteins and carbohydrates.
Extracellular
Intracellular

6. Cell membrane
Extracellular fluid
Intracellular fluid

7. Phospholipids bilayer
Cell Membrane
Phospholipids bilayer
= is thin, only two molecules thick and
continuous over the entire cell surface.
- Behaves like fluid, therefore the floating membrane proteins can move around all areas of the cell membrane.
- The lipid bilayer is almost impermeable to water and water soluble substances (glucose, urea, various ions).
- The lipid bilayer is permeable to fat-soluble substances (O2, CO2, and alchohols).

8. Cell Membrane Proteins Peripheral protein Integral protein
= are mostly glycoproteins
(proteins+carbohydrates).
- Two types of membrane proteins:
i) integral proteins: protrude all the way through the cell. These proteins provide pathways through which water and water-soluble substances can cross.
ii) peripheral proteins: occur on the membrane, and normally attached to the integral proteins. These proteins function as enzymes to control the chemical reactions inside the cell.
Integral protein

10. Cell Membrane Carbohydrates Carbohydrates + Carbohydrates Proteins + =
= are usually on the outside of the membrane attached
to the protein molecules. These carbohydrates which are usually attached to
proteins making glycoproteins play an important role in immune reactions and
also act as receptors on the surface of the cell.
Carbohydrates +
Proteins =
Glycoproteins
Carbohydrates +
Lipids =
Glycolipids

12. Cell membrane
Proteins may serve as:
carriers,
channels
and receptors

13. Endocytosis and Exocytosis
Ions, molecules and water can cross cell membrane by various methods which will be explained in future lectures. Large molecules (proteins and cell debris) have other means of exchange between ICF and ECF:
1- Endocytosis = formation of an invagination by the cell membrane to engulf extracellular fluid and other materials.
(phagocytosis, pinocytosis, and receptor-mediated endocytosis)
2- Exocytosis = is the reverse of endocytosis. Is used for secretion of
materials by the cell.
Nucleus
Cell
Invagination
Complete
engulfing
Engulfing and fussion
of the membrane

14. Endocytosis

15. Cell Cytoplams

16. Cytoplasm Jellylike matrix within the cell is known as cytoplasm.
- is not homogenous solution, but
is highly organized structure of
microtubules and microfilaments.

17. Cell Organelles - Lysosomes - Mitochondria
- Endoplasmic Reticulum Golgi Aapparatus

18. Lysosomes

19. Lysosomes
Membrane-bound organelles which contain digestive enzymes. The vacuole which contains the products of phagocytosis may fuse to a lysosome. The digestive enzymes breakdown the large molecules into smaller molecules.
Lysosomes: - fuse with food vacuole, - fuse with vacuoles containing bacterial debris, - engulf worn-out organelles, - rupture to initiate cell death

20. Mitochondria

21. Mitochondria Serve as the site for energy production- cell powerhouse.
Able to migrate throughout
the cytoplasm
It is believed that they are
able to reproduce. They have
DNA (primitive).

22. Endoplasmic Reticulum
- There are two types:
1- Rough Endoplasmic Reticulum (RER)= contains ribosomes on its surface. It is involved in protein synthesis, present in glandular cells.
2- Smooth Endoplasmic Reticulum (SER) = has no ribosomes on its surface. Is an storage area and were some cellular reactions occur, present in skeletal muscle for Ca++ storage.
RER
SER

23. Golgi Apparatus
Proteins which are synthesized in RER are transported and stored in the Golgi apparatus. Golgi apparatus functions:
1- Separation of different proteins according to their functions.
2- Modification of proteins
3- Package of proteins for delivery
to different parts.

24. Cell Nucleus
- Most cells have a single nucleus while some like skeletal muscle are multinucleated.
- Nuclear envelope: inner and outer membranes which surround the nucleus.
transport in and out of the nucleus?
Functions of DNA, RNA and mRNA?
Nuclear Pores

25. Structure of DNA
Deoxyriboneucleic Acid
Deoxyribose

26. DNA
Riboneucleic Acid
DNA

27. Protein Synthesis Genetic Transcription occurs in NUCLEUS
Genetic information is contained in DNA.
-To convert genetic code
(DNA code) to protein:
DNA code is first
transcribed into RNA
(genetic transcription).
Genetic Transcription
occurs in NUCLEUS

28. Protein Synthesis Protein Synthesis occurs in Cytoplasm amino acid
transfer RNA
Protein Synthesis
occurs in Cytoplasm

29. Protein Synthesis Nucleus mRNA Cytoplasm
The RNA (mRNA) which has been copied DNA code goes to cytoplasm at the ribosomes and starts the synthesis of proteins according to the transcribed code.
Nucleus
mRNA
Cytoplasm

30. Secretion of Proteins
The proteins which were synthesized in RER are delivered to Golgi apparatus for modifications, storage and secretion.