Unit 1 - section 6 Flashcards
What structure is responsible for maintaining the shape, structure and position of all cell organelles?
Cytoskeleton
What happens to the cytoskeleton during cell division?
It is remodelled
What is the cytoskeleton composed of?
Consists of different types of proteins extending throughout the cytoplasm, such as microtubules
What globular proteins are microtubules formed from?
Composed of hollow straight rods made of globular proteins called tubulins
What is the function of microtubules?
Govern the location and movement of membrane-bound organelles and other cell components
In what types of cell can you find can microtubules and where do they radiate from?
Found in all eukaryotic cells and radiate from the centrosome
What type of fibres do microtubules form during cell division?
Spindle fibres
What is the function of the cell cycle?
Regulates the growth and replacement of genetically identical cells throughout the life of the organism
What condition could result from the uncontrolled decreased in the rate of cell cycle?
Digenerative diseases
What condition could result from an uncontrolled increase in the rate of the cell cycle?
Tumor formation
Describe the 3 stages of interphase
G1 - first gap phase where proteins and organelles are synthesised
S - synthesis phase for continued growth and DNA replication
G2 - second gap phase where proteins and organelles are synthesised
What are the stages of mitosis?
Interphase - protein synthesis occurs and organelles are made. Cell grows and DNA is replicated
Prophase - chromatin condensed into sister chromatids and mitotic spindle forms between centrosomes
Metaphase - nuclear membrane breaks up and centrosomes are now at opposite poles. Chromosomes line up at metaphase plate. Microtubules attach to kinetochore
Anaphase - microtubules shorten pulling sister chromatids apart to opposite poles
Telophase - cell lengthens and nuclear membrane reforms around chromosomes at each pole. Chromosomes begin to uncoil
Cytokinesis - cytoplasm divides creating two new identical cells
What is the role of spindle fibres during M phase?
To divide the genetic material in a cell so that the chromosomes are divided equally between the two daughter cells that are forming
Where is the metaphase plate located?
On the equator of the cell
Describe the formation of daughter nuclei
Interphase - protein synthesis occurs and organelles are made. Cell grows and DNA is replicated
Prophase - chromatin condensed into sister chromatids and mitotic spindle forms between centrosomes
Metaphase - nuclear membrane breaks up and centrosomes are now at opposite poles. Chromosomes line up at metaphase plate. Microtubules attach to kinetochore
Anaphase - microtubules shorten pulling sister chromatids apart to opposite poles
Telophase - cell lengthens and nuclear membrane reforms around chromosomes at each pole. Chromosomes begin to uncoil
What is cytokinesis?
Stage where the cytoplasm divides creating two new identical cells
What are the 3 checkpoints that occur during the cell cycle and what are their functions?
G1 checkpoint - occurs towards the end of G1. Checks sufficient cell growth has occurred and that other conditions are satisfied before allowing the cell to enter S phase
G2 checkpoint - occurs at the end of G2. DNA replication must be completed for the cell cycle to continue
M checkpoint - occurs during metaphase and controls entry to anaphase. Checks that chromosomes are aligned correctly on the metaphase plate and therefore ensures that each daughter cell receives the correct number of chromosomes
Which checkpoint is the most significant for most cells?
G1 checkpoint
What occurs if the G1 checkpoint is not passed?
The cell will exit the cycle and switch to the G0 phase, a non dividing state, instead of completing the cycle and dividing
What happens to cell size at G1 checkpoint?
It is checked to ensure sufficient cell growth has occurred
What accumulates at G1?
Cyclin proteins
What is the role of Cdks in the control of the cell cycle?
As the cell size increases during G1, cyclin proteins accumulate and combine with kinases to form regulatory protein molecules which are known as cyclin-dependent kinases (Cdks)
Cdks cause the phosphorylation of proteins that stimulate the cell cycle. If a sufficient threshold of phosphorylation is reached the cell cycle moves onto the next stage
What occurs if the threshold of phosphorylation is not reached?
Cell is held at a checkpoint
Which protein is activated when DNA is damaged?
p53
What are 3 things that might occur if DNA is damaged during S phase?
p53 can activate DNA repair proteins to repair the DNA damage
p53 can stop the cell cycle at the G1 checkpoint - this can allow DNA repair proteins time to recognise and fix the DNA damage so the cell can restart the cell cycle
If the DNA damage is too severe p53 can initiate apoptosis
What is apoptosis?
Programmed cell death
What are the 2 classes of enzymes involved in apoptosis?
DNAases
Proteinases
How are death signals which originate from outwith or within cells triggered?
Outwith: cell death signals can be triggered from outwith the cell (for example from lymphocytes) a signal binds to a surface receptor activating protein cascades that trigger active caspases. These can activate DNAase that destroy the cell
Within: death signals can be triggered from within the cell (for example as a result of DNA damage) p53 proteins activate capase cascade. In the absence of growth factors apoptosis may be initiated
What is another solution that may give rise to apoptosis?
During human embryonic development programmes cell death occurs on the cells between the fifers and toes. Allowing individual digits to form
