Chromosomes & The Cell Cycle

Chromatin & Chromosome Composition

Made of:DNAProtein - histones

Chromosome Structure (after replication):2 chromatids – identical chromosomescentromere – holds sister chromatids togetherp and q arms

Chromosome Structure

Chromosome Numbers + TypesEach species has characteristic number

• Humans = 46• Chimpanzee = 48• Fruit fly = 8

Two Types:• Sex chromosome

» Humans = 2» XX = female» XY = male

• Autosome (body chromosome)» Humans = 44» 22 from each parent» Matching chromosomes = homologous chromosomes

(one from mom and one from dad)

Karyotype

Photograph of chromosomes in dividing cell.

Taken during metaphase-Like chromosomes are lined up next to each other.

Chromosomes and Cells

Diploid Cell• 2 sets of chromosomes – one

from dad and one from mom

• 2 sex chromosomes

• Body cells (somatic)

Haploid Cells• 1 set of chromosomes• 1 sex chromosome• Sex cells

» Egg » Sperm

Cell Division: Prokaryotes

-prokaryotes have cell walls but no nucleus and membrane bound organelles.

-have a single DNA molecule, circular chromosome attached to the cell membrane.

-examples: bacteria

-cell division is called binary fission.

Binary Fission-results in two new identical cells.

Cell Division: Eukaryotes

-cytoplasm and nucleus divides.

-two types of cell division in eukaryotes, mitosis and meiosis.

-Mitosis results in the production of two new identical cells containing a full set of DNA material.

-Meiosis results in the formation of gametes containing one half the DNA material.

The Cell CycleInterphase

G1

SG2

*G0

Cell Division: MitosisProphaseMetaphaseAnaphaseTelophase

Cytokinesis

Stages of Mitosis:

Final Details: Control of Cell Division

1. G1 checkpoint: proteins control whether or not the cell will divide and whether or not DNA synthesis can proceed.

2. G2 checkpoint: DNA repair enzymes check the newly replicated DNA.

3. Mitosis checkpoint: if all is good, proteins signal for mitosis to end and cells enter G1.

The proteins that control cell division are coded for by genes. If the gene is mutated, the proteins may be altered. This may lead to cancer.