The Cell Cycle

True or false? cells can divide continuously

false - new cells have to mature before dividing again

True of false? all cells have cell cycles of the same length of time

false - specialised cells usually take longer to divide

True or false? All cells can divide

false - some highly specialised cells e.g. nerve cells, loose the ability to divide altogether

What are the chemicals and the gene that trigger the movement from one phase to another in the cell cycle?

cyclins and tumour suppressor genes

What are the 2 main phases of the cell cycle?

interphase and the mitotic phase

In which phase of the cell cycle does a cell spend most of its time?

interphase

What are the 4 stages found within interphase?

G1, S phase, G2 and G0

Choose the correct words and fill in the blanks: The ‘_____’ phase where cells are/are not actively dividing. However there are still high/low levels of activity, as the cell carries out all its major functions.

resting, are not, high

What happens in the first growth phase (G1)?

cell increases in size, proteins from which organelles are synthesised are produced and organelles replicate, transcription of genes to make RNA

Fill in the blanks: In S (_____) phase, the chromosomes unwind so every molecule of DNA can be replicated, so that each once consists of a pair of identical ____ ____

synthesis, sister chromatids

In S phase there is a specific sequence in which the DNA replication is carried out. Do active or inactive genes get replicated first?

active

Why does S phase happen very quickly?

to reduce the chance of mutations occurring, as exposed DNA base pairs are more susceptible to mutagenic agents

What happens in G2?

cell continues to grow in size, energy stores increased, duplicated DNA is checked for errors, chemicals ensure the cell is ready for mitosis by stimulating the proteins involved in condensing chromosomes and in the formation of the spindle

What is the G0 phase?

when cells leave the cell cycle permanently or temporarily

State the 3 reasons why cells enter G0?

differentiation, DNA damage, senescence

What term describes programmed cell death, where cells permanently enter G0 to prevent mutations?

apoptosis

What is senescence?

the process by which a cell ages and permanently stops dividing (most cells can only divide a finite number of times) but doesn’t die (it can still function)

Give an example of a cell that only enters G0 temporarily?

lymphocytes

What are the 2 stages of the mitotic phase?

mitosis and cytokinesis

Fill in the blanks: in eukaryotic cells the DNA that makes up chromosomes is wrapped around ____ proteins to form ____

histone, chromatin

Fill in the blanks: when DNA is replicated the chromosomes uncoil and the DNA replicates producing a pair of ___ ____ held together by a ___

sister chromatids, centromere

How many chromosomes do human have?

46

How is the eukaryotic cell cycle regulated?

checkpoints

What are the 2 main checkpoints called?

G1/S (restriction point) and G2/M

Why are checkpoints needed?

To ensure a cell only divides when it is the correct size, the replicated DNA is error free and the chromosomes are in their correct position

True or false? checkpoints ensure that DNA is only replicated once and is replicated correctly reducing the risk of uncontrolled division that would lead to tumours

true

What type of molecules are checkpoints usually made from?

enzymes

What 3 things could happen to a cell if the checkpoints detect errors?

the errors are repaired, the cell is sent to G0 or the cell destroys itself to prevent passing on mutations

What is the process called by which prokaryotic cells divide?

binary fission

Describe what happens in binary fission

DNA is replicated and the two new loops are pulled to opposite ends of the cell, which grows to the limit of its size and splits in two, developing a new cell wall

Which 2 components of eukaryotic cells divide by binary fission?

mitochondria and chloroplasts

What is the name of the checkpoint found in the mitotic phase of the cell cycle?

spindle assembly checkpoint / metaphase checkpoint

What does the spindle assembly checkpoint check for?

the correct attachment and alignement of chromosomes to spindle fibres