Animal Cell Structure and Function

An animal cell is a eukaryotic cell (Eu: true; karyo: nucleus) therefore with true nucleus. The genetic material, DNA is surrounded by a nuclear membrane. Membrane bound organelles like mitochondria, SER, RER etc. are also present.

1. Nucleus (Controlling center of the cell): is a double membrane bound organelle where DNA is present. It is the site where DNA; the hereditary material is found which controls the activities of the cell. It consists of a nuclear membrane or envelope with pores, the nuclear sap or nucleoplasm, chromatin fibers (DNA) and nucleolus. Detailed notes on Nucleus

2. Nucleolus: Nucleolus are membrane less prominent spherical colloidal bodies rich in RNA present in the nucleus.

Function: It is the site where ribosomal subunits, 40S and 60S are synthesized and separately assembled and dispatched into the cytoplasm where final assemblage into complete ribosome occurs. Detailed notes on Nucleolus

3. Rough Endoplasmic reticulum (RER): RER consists of interconnected network of membrane vesicles studded with ribosomes. On the membrane of RER, ribosomes are attached to transmembrane glycoproteins called ribophorins I and II.

Function: synthesis of secretory and membrane proteins and post translation modification (protein glycosylation) Detailed notes on ER

4. Golgi apparatus (GA): Consists of parallelly arranged flattened membranous sacs that lacks ribosomes. Proteins synthesised in the RER pass through different regions of golgi apparatus (cis, median and trans golgi) where it undergoes further modification.

Function: GA is the sorting centre of the cell. In plant cells, GA is involved in the deposition of primary and secondary wall materials (pectin, cellulose etc).

In animal cells, GA is involved in packaging and secretion of hormones, mucus etc. Other functions include protein sorting and targeting.

Involved in the formation of lysosome, acrosome etc. Detailed notes on GA

5. Smooth Endoplasmic reticulum (SER): interconnected network of membrane vesicles without ribosomes; that’s why called “smooth”.

Function: lipid biosynthesis including cholesterol and phospholipid synthesis and drug detoxification

6. Ribosome 80S: are made up of several rRNA molecules and ribosomal proteins, simply an RNA-protein complex.

Function: Protein synthesis. Detailed notes on ribosomes

7. Mitochondrion: semi-autonomous, double membrane bound organelle with DNA

Function: ATP synthesis through cellular respiration; therefore called as “power house of the cell”, beta oxidation in matrix. Detailed notes on Mitochondrion

8. Peroxisome: are microbodies or self-duplicating, single membrane bound organelles present in all eukaryotic cells. They contain oxidative enzymes, such as catalase and urate oxidase, at such high concentrations.

Function: compartment for oxidation reactions, H₂O₂ scavenger; chemical detoxification, lipid biosynthesis Detailed notes on peroxisome

9. Lysosome: also called as “suicidal bags” as its contains strong digestive enzymes.

A single membrane bound organelle present only in animal cells. Lysosome lumen has a slightly acidic internal pH (pH 4-5), optimum pH for working of digestive enzymes.

Function: intracellular and extracellular digestion, cellular autophagy or autolysis of infected cells. Detailed notes on lysosome

10. Centriole: paired barrel-shaped organelles near the nuclear envelope

Function: formation of spindle fibres and regulating the movement of chromosomes during cell division.

11. Cytoskeleton: made up of microfilaments, intermediate filaments and microtubules; also called as “cytomusculature”.

Function: structural frame work of the cell, distribution, positioning and movement of organelles. Detailed notes on cytoskeleton

12. Plasma membrane: selectively permeable membrane made up of phospholipid bilayer and proteins

It encloses the interior of the cell, regulating the flow of materials in and out of the cell. Detailed notes on plasma membrane

13. Flagella: are fine long whip like structures for locomotion. Rotation of flagella propels bacteria forward. It is made up of microtubules (9+2 arrangement).

Detailed notes on flagella

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