Lecture 2 - Cell Division & Apoptosis Flashcards Preview

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What is embryogenesis?  

Embryogenesis is the process by which the embryo forms and develops.


What is Hematopoiesis? 

It is the production of all the different blood cells found in blood from a haemopoietic stem cell. 

You might like this video: 

Hematopoiesis by Khan Academy 



What must take place before cell division can occur?  

  1. The cell must grow to twice its original size 
  2. The cell must duplicate all its organelles 
  3. The cell must replicate all its chromosomes 
  4. The dividing cell must separate two identical sets of chromosomes for each new daughter cell. 


Which type of cell division is the simplest and name the type of organisms that undergo this type of cell division? 

Binary fission is the simplest type of cell division and it is the prokaryotes that utilise this type of cell division. 


Name the phases of the cell cycle. Explain what goes on at each phase. 

  1. The G1 phase - The G1 phase is a growth phase where the cell begins to grow to be twice its original size. 
  2. The S phase - In S phase, the cell's DNA replicates. 
  3. The G2 phase - The G2 phase is another growth phase where the cell duplicates its organelles 
  4. The M phase - aka the mitotic phase, this is the phase when mitosis occurs. 
  5. The C phase - In the C phase cytokinesis occurs and two new cells are formed each carrying identical DNA.  


Which phases of the cell cycle make up interphase? 

  1. G1 phase
  2. S phase 
  3. G2 phase 


How do the chromosomes appear throughout interphase? 

They appear as their uncondensed state called chromatin which looks like yarn in a ball of yarn. 


Does the double nuclear membrane of the nucleus remain intact throughout interphase? 




Are microtubules (MTs) a component of the cytoskeleton? Where do microtubules originate and extend from? 

Microtubules are 1 of 3 components of the cytoskeleton. The other 2 are intermediate filaments and microtubules.  


Where do microtubules originate and extend from? 

Microtubules originate and extend from Microtubule Organising Centres (MTOCs). The major MTOCs of most animal cells is centrosomes. 


Describe the status of the nuclear envelope (membrane), centrosomes, microtubules and DNA in the G1 phase  

  • The DNA is still in its uncondensed form of chromatin.  
  • Microtubules are extending from one centrosome 
  • The nuclear envelope is intact 


Describe the status of the nuclear envelope (membrane), centrosomes, microtubules and DNA in the S phase  

  • The DNA still looks like chromatin but is now replicating from origins of replication.   
  • Microtubules are extending from a duplicated centrosome (so microtubules are extending from two centrosomes).  
  • The nuclear envelope is intact.  


Describe the status of the nuclear envelope (membrane), centrosomes, microtubules and DNA in the G2 phase  

  • The DNA has successfully been replicated but it still looks like chromatin.
  • Microtubules are extending from a duplicated centrosome (so microtubules are extending from two centrosomes). The two centrosomes are beginning to move away from each other.  
  • The nuclear envelope is intact.  


Name the five stages of the M phase in the correct order.  

  1. Prophase 
  2. Metaphase 
  3. Anaphase 
  4. Telophase 
  5. Cytokinesis 

Note that Cytokinesis is part of the M phase but it is absolutely not part of mitosis. Mitosis is defined as being nuclear division whereas cytokinesis is defined as being cytoplasmic division. M phase does not mean mitosis phase, it means mitosis and cytokinesis phase. There is no such thing as an M (mitosis) phase and C (cytokinesis) phase. 


Describe the Prophase stage 

The chromatin starts to condense. Th chromosomes are becoming visible, shorter and thicker.  

The microtubules extending from the centrosomes push the centrosomes away from each other along the surface of the nucleus. 

The microtubules attach to chromosomes forming the mitotic spindle. 

The nuclear envelope breaks down. 


Describe the Metaphase stage 

Chromatin is fully condensed and visible as separate elements. 

The chromosomes are moved by the MT mitotic spindle to the metaphase plate.

MTs are attached to centrosomes at one end and attached to the kinetochores on the centromeres of chromosomes.   


Describe the Anaphase stage 

Sister chromatids pulled apart to create two identical single-chromatid chromosomes. Sister chromatids that were once joined at the centromere now move to opposite poles of the cell. 


Describe the Telophase stage 

Two sets of identical single-chromatid chromosomes are now at opposite poles of the cell. They start to condense to form chromatin again. 

Two nuclear envelopes at opposite ends are now reforming around the two sets of single-chromatid chromosomes creating two separate nuclei. 


Describe cytokinesis in animal cells 

A cleave furrow forms between the two nuclei and it splits the parent cell into two daughter cells each with their own identical nuclei and DNA. 


Describe cytokinesis in plant cells 

Plant cells have rigid cell walls composed of cellulose. a septum grows down the plane of the metaphase plate splitting the large cell into two smaller daughter cells. 


What are the three main checkpoints in the cell cycle? What do these checkpoints do? 

  • G1 checkpoint - this checkpoint occurs towards the end of G1. The cell can only progress to the S phase if it has sufficiently grown during the G1 phase.  
  • G2 checkpoint -  this one occurs at the end of G2 and it checks to see if DNA replication has been completed. 
  • M checkpoint - this is a checkpoint that occurs at the end of metaphase. It checks to see whether the chromatids are arranged correctly on the metaphase plate ensuring that each daughter cell receives the same number of chromosomes before allowing the cell to progress to anaphase. 

Information from Scholar Advanced Higher Biology  


What is the most important checkpoint in the cell cycle? 

The G1 checkpoint 

If a cell progresses past this checkpoint then it will most likely pass all other checkpoints and divide successfully. If the cell does not get the "go ahead-signal" at the G1 checkpoint it will exit the cell cycle and switch to a non-dividing stage called the G0 phase. 

Info from A.H. Biology Scholar 


Which substance increases and accumulates during progress through the G1 phase? 


Cyclin is a family of proteins that control the progression of cells through the cell cycle by activating cyclin-dependent kinase (Cdk) enzymes.​

Info from A.H. Biology Scholar


What are CDKs and what do CDKs do?

CDKs stand for cyclin-dependent kinases. CDKs phosphorylate particular proteins, helping the cell to progress to the next stages of the cell cycle. 

A threshold of phosphorylation has to be met before a cell can move to the next stage of the cell cycle. 


Describe how a cell progresses to the S phase from the G1 phase referring to the action of G1-CDK.  

G1-CDKs phosphorylate a protein called Retinoblastoma (Rb).

Before Rb gets phosphorylated, Rb binds and thus inhibits a transcription factor (its called E2 promoter-binding–protein-dimerization partner (E2F-DP). Transcription factors are proteins that help turn a gene "on" or "off" by binding to specific sequences on DNA). E2F-DP actually increases transcription of genes that are required for S phase.  

When Rb gets phosphorylated by a G1-CDK it becomes inhibited and the transcription factor gets released from Rb and is allowed to bind to its particular target DNA sequence, increasing transcription of essential genes that are required to kick-start DNA replication, so the cell can move to S phase. 

There is a phosphorylation threshold that has to be met before the cell can move to S phase so there has to be enough of these CDK-Rb complexes being made. 

Info from A.H. Biology Scholar




What happens when DNA is damaged during a stage in the cell cycle. 

DNA damage triggers the activation of several proteins that can stimulate DNA repair, arrest the cell cycle or induce the cell to undergo apoptosis. 

One of these "several proteins" is called p53 and it has been called "the guardian of the genome" (many cancers are caused by mutations in the P53 gene that makes p53). 


Name the three different responses a p53 could make in recognising DNA damage. 

• it can activate DNA repair proteins to repair the DNA damage;
• it can arrest the cell cycle at the G1 checkpoint, which means that the cell cycle
halts at this point - 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, it can initiate apoptosis (programmed cell death).

Notice that as we go down the list the severity of the DNA damage increases and the more extreme the responses of P53 become.  


Helpful Pictures 


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