Ch. 12 and 13: Cellular Basis of Reproduction and Inheritance
Genes carried on single circular DNAmolecule
• Up to 500x cell length
Complexed with few proteins and attached to plasma membrane at one point
Prior to cell division, genome copied
Copies attached to adjacent parts of membrane
Cell elongation and new plasma membrane separates two genomes
Plasma membrane pinches through cell
Eukaryotes have large, complex, multiple chromosomes
Human cells contain about 30,000-35,000 genes
Organized into separate, linear chromosomes
DNAcomplexed with proteins
Just prior to division, chromosomes become visible
Remain visible during division process
Somatic cells are body cells (not sex cells)
Ex. Hair cells
These cells need to contain the full set of chromosomes so that all the directions
for functions and activities of the cell can be carried out.
Normally you inherit 23 chromosomes from each of your parents
This complete set of chromosomes (46) is known as the Diploid Number in
Sex cells are known as gametes
These cells have half of the number of chromosomes that a body cell would have.
In humans this number is 23
Sooooo...Somatic (body) cells contain the diploid number of chromosomes
compared to sex cells (haploid number)
Somatic cells-46 chromosomes (2n=46)
Sex cells-23 chromosomes (n=23)
What is a chromosome?
Prior to cell division, chromosomes are duplicated
Visible chromosomes consist of two identical sister chromatids attached at
Sister chromatids can be separated…
Once sister chromatids separate they are again called un-replicated chromosomes
I know you are all thinking: WHAT?????
Humans have 23 pairs of chromosomes
1 [Type text] [Type text] [Type text]
They get numbers 1-23 from Mom and 1-23 from Dad = 46 (in males, 23 is non-d
These 46 chromosomes are found in somatic cells
Sex cells (gametes) have only 23
Each species has a specific diploid number
The cell cycle is like an “ alarm clock” that tells the cell when it is time to do
some essential activities and when to divide.
It is regulated by many chemicals inside the cell.
Cell cycle divided into several steps (phases)
Interphase represents 90% or more of cycle time
G -Cell increases in size and increases supply of proteins and organelles
S-DNAsynthesis occurs (Copy DNA)
G -2ell prepares for division, increases supply of proteins necessary for division,
checks for DNA damage
G –0cell stops progressing through cycle- will not divide
G Th0 =is a very important phase of cellular activity
The cell has the opportunity to stop progressing towards division, or DNAsynthesis
Why would this be important for a cell??????
Cells can phase into and out of G f0om several other cell cycle phases, its like an
Different cells are in various phases of cycle even in same tissue
Also Different Tissues May Regulate Cycle Differently
Ex. Hair Divides Constantly
Nerve Tissue Never Divides InAdults
Adult Liver Tissue Does Not Divide, Except For Repair
How does a cell progress through the cell cycle?
Many biochemicals stimulate the transition
One of them is a Kinase
AKinase is an enzyme that catalyzes the transfer of a phosphate group fromATP to
A Cdk is a cyclin dependent kinase
MPF (maturation promoting factor) is a co- chemical that is attached to Cdk
These chemicals stimulate the transition to cell division. When they are HIGH, the
cell will DIVIDE.
Why do we care about this?
BECAUSE CYCLINAND CDK LEVELS AREALTERED IN CANCER