Cell cycle Flashcards
What is the cell cycle?
A sequence of events that leads to the reproduction of a cell
Before cell division
- Chromosome replication and segregation
- Cell growth
- Separation of organelles
- Gap phases (provides time for cell growth)
How does the cell cause cell division?
When cells grow DNA/mass ratio decreases. Then chromosomes and DNA duplicate causing an increase in ratio and so the cell doubles in size for division
What are the 4 nitrogenous bases in DNA?
Adenine, guanine, thymine and cytosine
What is the basic structure of DNA?
Nitrogenous bases connected together via pentose sugars and phosphate
Eukaryotic DNA replication
- Takes place in nucleus
- 4+ types of polymerases
- Slow
- Occurs in S phase
Prokaryotic DNA replication
- Takes place in cytosol
- 1-2 types of polymerases
- Fast
- Occurs throughout cell cycle
1st step of DNA replication
2 strands of DNA are in a straight bond which is then separated by an initiator protein to form a replication bubble
2nd step of DNA replication
DNA becomes untwisted by DNA helicases to form a Y shaped replication fork by breaking hydrogen bonds between bases
3rd step of DNA replication (single-stranded DNA-binding (SSB))
2 single-stranded template strands are formed which bind to proteins to prevent re-joining
What are DNA topoisomerases?
They are part of SSB and relieve tension
4th step of DNA replication
RNA primase synthesises a short RNA primer which attaches to a template strand
5th step of DNA replication
DNA polymerase causes the addition of nucleotides to the RNA primer where it forms a base pair with a nucleotide on the template strand of DNA
What are Okazaki fragments?
Small fragments of DNA nucleotides
What are the 4 periods of the cell cycle?
G1, G2, M and S
G1 period
- Cell growth
- Preparation of chromosomes for replication
- Duplication of cell components
S period
- When DNA is made
- Each chromosome has many origins of replication
G2 period
- Cell prepares for M period
- Genes are expressed
M period
- Mitosis or meiosis occurs
- Chromosomes are condensed and separated
- Cell divides
Mitosis
- Occurs in somatic or body cells
- Asexual reproduction for healing cells and growth and development of cell body
- One cell division
- 4 stages of cell division
- No independent assortment at metaphase
- Separation of sister chromatids at anaphase
Meiosis
- Occurs in reproductive cells
- Only needed for sexual reproduction
- 2 cell divisions
- 8 stages of cell division
- Independent assortment of homologous chromosomes at metaphase
- Separation of homologous chromosomes and sister chromatids at anaphase
