The Cell Cycle Flashcards
Name the phases of the cell cycle
G1, S , G2, M, G0 (only sometimes)
What happens in the G1 phase of the cell cycle
Prep for S phase
What happens in the S phase of the cell cycle
DNA synthesis when the chromosomes are duplicated in DNA replication
What happens in the G2 phase of the cell cycle
- cells with duplicated chromosome are held together at the centromere
- another prep phase, duplicate organelles and increase cytoplasm
What happens in the M phase of the cell cycle
- cell division
- nuclear division
What happens in the G0 phase of the cell cycle
Resting phase, no division is taking place
Which of the phases does interphase consist of?
G1, S, G2
What happens in prophase?
- chromosomes condense
- centrosomes move to opposite poles
- mitotic spindle forms
What happens in prometaphase?
- Breakdown of the nuclear envelope
- chromosomes attach to the mitotic spindle
What happens in metaphase?
- centrosomes are at opposite poles
- chromosomes are at their most condensed
- chromosomes line up at the equator or the mitotic spindle
What happens in anaphase?
- sister chromatids separate synchronously, each new daughter cell moves to the opposite spindle pole
What happens in telophase?
- Chromosomes arrive at the spindle poles
- chromosomes decondense
- nuclear envelope reforms
What happens in cytokinesis?
Actin and myosin accumulates between the poles of the mitotic spindle beneath the plasma membrane. The ring contracts and forms an indentation or cleavage furrow, which divides the cell into two new rings
What is a metaphase plate?
A cross section plane along which the chromosomes are lined up down the centre of the cells in metaphase
What are the three types of spindle microtubules?
Astral , kinetochore, interpolar
What is the function of the astral microtubules?
Orientation and positioning of the spindle inside the cell (also influences the site of cytokinesis)
What is the function of kinetochore microtubules?
They project from the centrosome and connect with the kinetochore
What is the function of the interpolar microtubules?
They extend from the poles and interact in the middle of the zone of interdigitation
What is a mitotic spindle?
A microtubule machine that separates the duplicated chromosomes
Where (/when) does the mitotic spindle form?
Assemble during prophase from the centrosomes
Can the cell cycle proceed if only some kinetochore microtubules are attached to the kinetochores?
No, all of them have to have attached
How do the kinetochore microtubules attach to the kinetochore?
Lots of proteins on the outer plate of the kinetochore that can interact with the microtubules also fibrous corona
What does the fibrous corona have that makes it important?
Lots of proteins that have functions around microtubule capture and spindle assembly
Why does the fibrous corona have to be disassembled before anaphase
To avoid mistakes in chromosome segregation
Give the steps in the centrosome cycle
The centrosomes are duplicated during interphase, then migrate to opposite poles in preparation for M phase
What does the centrosome consist of?
A pair of centrioles surrounded by peri-centriolar material
How do we make sure all new cells have all the organelles?
Lots of copies of organelles in the parent cell, which are randomly scattered.
When the cell divides there is a roughly equal presence of organelles in each.
Give a definition of meiosis
Specialised cell division that starts with one diploid cell and ends with four haploid cells
What happens in meiosis I?
Homologous chromosomes line up on the spindle and separate to opposite spindle poles
What happens in meiosis II?
Chromatids line up on the spindle and separate to opposite the spindle pole
What does recombination occur between?
Homologous chromosomes
What are examples of non-fatal autosomal syndromes?
Trisomy 21- downs
Trisomy 18- Edward’s
Trisomy 13- patau
What is non-disjunction?
When the homologues fail to separate from one another, either at meiotic division I or meiotic division II
What syndromes are there when the sex chromosomes go wrong?
XO- turners
XXX- triple X
XXY- kleinfelter
What are the cell cycle regulators?
Cyclin dependant kinases (Cdks)
Cyclins
What do Cdks do?
They’re active when bound to cyclin and they phosphorylate target proteins
When do cyclins work?
There’s different cyclins produced at different phases in the cycle
When are there checkpoints in the cell cycle?
G1, G2 and metaphase
What is checked at the G1 checkpoint?
DNA for damage
Extra cellular environment
What is checked at the G2 checkpoint?
Check DNA for damage
Check DNA has replicated
What is checked at the metaphase checkpoint?
Are all chromosomes aligned on the mitotic spindle?
What are the two cyclins in yeast and what do they trigger?
S cyclin triggers S phase
M cyclin triggers M phase
What are the cyclins called in humans?
Cyclin D (CDK4) Cyclin E (CDK2) Cyclin A(CDK2) Cyclin B (CDK1)
What does cyclin activation trigger?
The next step in the cell cycle
What happens to the levels of CDK and cyclin levels throughout the cell cycle?
CDK stays fairly stable
Cyclin varies
What is neoplasia?
Uncoordinated cell growth
How does neoplasia happen?
The cells escape normal cell cycle regulation so there’s no barriers to progression
What are the tumour suppressor genes?
p53
pRB
