Unit 4 - DNA Structure + Cell Cycle/Cyclins

Question 1

What are the different phases included in the cell cycle?

Answer 1

G1, S, G2, Mitosis

and G0

Question 2

G1 phase

Answer 2

1st phase of the cell cycle

preps the cell for life, works on basic needs for cell to live (nutrients, size, etc). No replication occuring at this stage

Question 3

S phase

Answer 3

Preps the cell for mitosis
- Replicates the DNA and genetic material

Question 4

G2 phase

Answer 4

Cell grows more in size

Increases nutrient contents
Preps for mitosis

Question 5

M phase

Answer 5

Mitosis occurs here

Question 6

G0 phase

Answer 6

A permanent G1 phase

• cell is done with differentiation and no longer has to divide (before it can even start going into the cell cycle)
• If cell cannot go through mitosis because its fucked up but it can still live, so it goes into a permanent g1 phase

Question 7

How are the cell cycles controlled? How does the cell know when to go to the next one?

Answer 7

Through the expression of cyclins and when they go away (protein turnover) and through the presence of CDKIs

Question 8

How do the cyclins result in the change of the cell cycle?

Answer 8

There are CDKs which are kinases that activate certain pathways which can initiate the gene expression of a specific growth inhibitor

• cyclins activate these kinases - specific cyclins go towards specific cdks –> expressing different molecular complexes

Question 9

What happens when there is dna damage

Answer 9

DNA damage lets out of a signal codes for CDKIs which match with the CDKs and block the cyclins from matching up with them.
–> pauses the cell cycle
cyclin + cdk cannot code for
protein to allow for the next
cell cycle to begin

p53 ubiquitin tag is taken off so it is allowed to build into the cell more
–> causes for it to be more present in the cell and allow for it to reach threshold and actually be able to activate pathways that express dna repair proteins

CDKIS : pause cell cycle
p53 : initiate DNA repair proteins and check if it is repaired

Question 10

What happens if the DNA damage was unable to be fixed?

Answer 10

The cell will either go to programmed cell death (Apoptosis)

or if it is not damaging and it can just exist it will go into an arrest G0 phase

Question 11

What are the 3 things that mainly make up dna?

Answer 11

1. Bases
2. Sugar Backbone
3. Phosphodiester Bonds

Question 12

What is the sugar backbone of dna?

Answer 12

Frame work for the base pairing, holds the dna bases together
1. nucleotide = nucleoside + phosphodiester bond
5 Carbon Sugar, with Hydroxyl group and base pairing

1 nucleoside held together by phosphodiester bond

Question 13

The phosphodiester bond is between which two molecules and where in between the nucleoside

Answer 13

Hydrogen

• OH Hydroxyl group and the 5th Carbon CH2

Question 14

Base pairings

Answer 14

G - C
A - T

Question 15

Which bases are purines

Answer 15

A and G

Question 16

Which bases are pyrimidines?

Answer 16

C and T

Question 17

How are the bases attached

Answer 17

hydrogen bonds

Question 18

which base has a stronger hold

Answer 18

G and C
- they have 3 hydrogen bonds while C and T only have 2

Question 19

What does the G1 phase do

Answer 19

checks if the cell is okay by itself, if it grew correctly and everything is okay
–> no it might go into a G0 phase if it cannot be fixed

Question 20

What does the G2 phase do?

Answer 20

checks if the S phase went smoothly, did the dna replicate completely

Question 21

What does the spindle checkpoint do?

Answer 21

checks if the metaphase to anaphase transition went smoothly

Question 22

What is the Cyclin D Phase do?

Answer 22

Initiates the G1 phase.
determines if the cell is well made and has good nutrients, so it will stay consistent until mitosis is done, it is present and once cell dies and no longer needs to focus on its nutrients it will go away

Question 23

When is Cyclin D activated

Answer 23

grows in G1
stays consistent through S and G2
decreases in M

Question 24

What does Cyclin E initiate?

Answer 24

Initiates the dna replication + S phase

Question 25

When is Cyclin E Activated

Answer 25

• Hightens during the transition between G1 to S
  phase –> when DNA replication happens
• Activated at end of G1 and beginning S phase

Question 26

What is Cyclin A initiated?

Answer 26

• slowly increases all the way to G2 phase
• rapidly increases once DNA replication stops
• Reaches threshold once G2 phase and then goes back down in G2 phase

Question 27

When is Cyclin B activated?

Answer 27

Initiates mitosis

Question 28

When is Cyclin B initiated?

Answer 28

Builds up through s to g2 phase and when it gets closer it builds up because it knows it will probably as it passes checkpoints
- once M it decreases

Question 29

When is p53 activated

Answer 29

through DNA damage