The Structure of a Cell

Overview of an animal cell

Intermediate Filaments:

FUNCTION: providing a supporting framework within the cell
Microtubules:

FUNCTION: are used to move things from one place in the cell to another
Lysosomes:

FUNCTION: Lysosomes repair wounds in the plasma membrane.
Nucleus:
- Contains the chromosomes of the cell
- Here is a picture of all the chromosomes of a human with Down's syndrome:
  
  Notice the extra chromosome 21
- Here is a picture of a highly magnified DNA strand:
  
  Notice the double helix....
  FUNCTION: Chromosomes contain all the genes - the genes determine the properties/functions of a cell.
  A gene is a portion on a chromosome that can be used to make a specific type of RNA molecule.
  See here on how a gene "express" itself: click here
Ribosomes: roughly sherical - are the protein-synthesizing machines of the cell
FUNCTION: they translate the information encoded in messenger RNA (mRNA) into a polypeptide
Mitochondria: are membrane-enclosed organelles

FUNCTION: Their main function is the conversion of the potential energy of food molecules into ATP (energy molucle of living organism)
The way a living cell extracts enertgy from ATP molecule is through the "Citric Acic Cycle":

An extremely interesting fact about mitochondria:
- Mitochondria (and chloroplasts in plants) can only arise from preexisting mitochondria (and chloroplasts).
  They cannot be formed in a cell that lacks them because the nuclear genes encode only some of the proteins of which they are made - but not all !!!
- Scientists can and have used this fact to trace the lineage of the mother side: when a sperm cell and an egg cell forms an embryo, the embroyo's mitochondria contain some genes that are exclusively from the mother !!!
- BTW, linearage of the father side can be traced through the males' Y chromosome.

How a gene expresses itself:

The process occurs in two steps:
1. Transcription DNA -> RNA
2. Translation RNA -> protein
Example:
- DNA is a duble helix, consisting of a "sense" and an "antisense" strand
- The example shows the transcription of the antosense strand DNA into RNA (messenger RNA or mRNA).
- The messenger RNA will be transported out of the nucleus and will itself cause the formation of peptide by the translation process.

Mitosis: how life muliplies

After a mitosis cell division, one cell divides itself into two identical cells.

Meiosis: how new life begins

After a meiosis cell-division, one cell divides itself into two diferrent cells, each with half the number of chromosomes.
During the meiosis, some genes may cross over to other chromosomes...

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