CELL CYCLE

Question 1

WHAT ARE THE TWO CONTROL FACTORS OF THE CELL CYCLE

Answer 1

1. ASSOCIATION OF CYCLINS WITH CDKS

2. MECHANISMS TO STOP THE CELL CYCLE IF THERE ARE PROBLEMS IE CHECKPOINTS

Question 2

WHAT DECISIONS CAN A CELL TAKE

Answer 2

QUIESCENT, PROLIFERATE, DIFFERENTIATE

Question 3

WHAT HAPPENS IN G1

Answer 3

THE CELL GROWS IN PREPARATION FOR DNA REPLICATION AND CERTAIN INTRACELLULAR COMPONENTS UNDERGO REPLICATION

Question 4

WHAT HAPPENS IN S PHASE

Answer 4

THIS IS WHERE DNA IS REPLICATED

Question 5

WHAT HAPPENS IN G2

Answer 5

RAPID CELL GROWTH AND PROTEIN SYNTHESIS

Question 6

WHY DO CYCLINS DECREASE THROUGHOUT THE CYCLE

Answer 6

TO ENSURE THE PROCESS IS UNIDIRECTIONAL

Question 7

WHY ARE D CYCLINS DIFFERENT

Answer 7

D CYCLINS ARE CONTROLLED BY EXTRACELLULAR SIGNALS - INTEGRINS AND ECM ATTACHMENTS

Question 8

UP UNTIL WHICH POINT IS THE CELL UNDER EC CONTROL

Answer 8

R POINT. AFTER R POINT THIS IS A CELL AUTONOMOUS PROCESS. CYCLINS AND CDKS FORM COMPLEXES THAT ACTIVATE THE SUBSEQUENT PHASE AND INHIBIT THE PREVIOUS.

Question 9

HOW ARE CYCLINS AND CDKS REGULATED

Answer 9

CDK INHIBITORS

Question 10

WHAT INHIBITS CYCLIN D AND ITS CDK4/6 COMPLEXES

Answer 10

CKI SUCH AS P16INK4A/P15INK4B/P18INK4C/P19INK4D

Question 11

WHAT INHIBITS ALL CYCLINS AND THEIR COMPLEXES APART FROM D

Answer 11

CKI SUCH AS P57KIP2/P27KIP1/P21CIP1

Question 12

HOW DO CYCLINS DRIVE THE CELL CYCLE

Answer 12

Cyclins drive the events of the cell cycle by partnering with a family of enzymes called the cyclin-dependent kinases (Cdks). A lone Cdk is inactive, but the binding of a cyclin activates it, making it a functional enzyme and allowing it to modify target proteins.

Question 13

CYCLIN CDK COMPLEXES AT WHICH STAGES

Answer 13

G1: CDK4 and CDK6 depend on the association with cyclin Ds (D1,D2 &D3 = D-type cyclins)
After the R point: E-type cyclins associate with CDK2  phosphorylation of substrates required for entry in S phase
S phase: A-type cyclins replace E cyclins in complex with CDK2 - S phase progression. Later in S-phase, A-type cyclins associate with CDK1
G2: B-type cyclins replace A-type ones in the complex with CDK1
M phase: B-type cyclins/CDK1 - mitosis triggering
G0 to G1: mediated by cyclin C/CDK3 complex

Question 14

WHAT IS THE RESTRICTION POINT FOR

Answer 14

1. IS THE CELL BIG ENOUGH
2. IS THE ENVIRONMENT FAVOURABLE
3. IS THERE ANY DNA DAMAGE

Question 15

WHAT IS G2 CHECKPOINT FOR

Answer 15

1. IS ALL DNA REPLICATED
2. IS THE CELL BIG ENOUGH
3. IS THE ENVIRONMENT FAVOURABLE

Question 16

WHAT IS THE METAPHASE CHECKPOINT FOR

Answer 16

ARE THE CHROMOSOMES ALIGNED ON THE SPINDLE

Question 17

HOW DOES THE RESTRICTION CHECKPOINT OCCUR

Answer 17

1. CYCLIN D AND CDK4/6 FORM A COMPLEX IN G1
2. THIS COMPLEX ALLOWS PHOSPHORYLATION OF PRB (THAT IS BOUND TO E2F)
3. PHOSPHORYLATION OF PRB INACTIVATES THE PROTIEIN THEREBY FREEING E2F TO BE TRANSCIBED
4. TRANSCIPTION OF E2F PRODUCES CYCLIN E AND CDK2 ALLOWING PROGRESSION TO S PHASE

E2F REGULATIONS EXPRESSION OF CDK2 , CYCLIN E AND A
IF THERE IS SIGNICANT DNA DAMAGE P53 STIMULATES PRODUCTION OF P21
P21 INHIBITS ALL CDK COMPLEXES WHICH CAUSES ARREST OF THE CELL CYCLE
TUMOUR SUPPRESSOR RETINBOBLASTOMA PROTEIN INHIBITS E2F EXPRESSION
CYCLIN D AND ITS CDK4/6 COMPLEXES PHOSPHORYLATE PRB WHICH LEADS TO ITsINACTIVATION LEADING TO EXPRESSION OF E2F
E2F CAUSES EXPRESSION OF CYCLIN E AND CDK2 THEREBY S PHASE CAN CONTINUE

Question 18

WHAT HAPPENS UPON DETECTION OF DNA DAMAGE

Answer 18

1. ATM/ATR ASSOCIATES WITH SITE OF DAMAGE
2. THIS ACTIVATES KINASES SUCH AS CHK1//CHK2
3. THIS CAUSES PHOSPHORYLATION OF P53
4. P53 CAN CAUSE P21 GENE TO ACTIVATE ENCODING CYCLIN DEPENDENT KINASE INHIBITORS THEREBY ARRESTING THE CELL CYCLE

Question 19

WHAT ARE THE CHOICES OF A DAMAGED CELL AND HOW CAN THIS CHANGE

Answer 19

A DAMAGED CELL CAN ARREST UNTIL DAMAGE IS REPAIRED, IF IN G1 IT CAN REVERT TO G0 OR IT CAN TRIGGER APOPTOSIS. THE BALANCE BETWEEN REPAIR AND APOPTOSIS CAN CHANGE OVER TIME.

Question 20

WHAT ACCOMPANIES FORMATION OF MOST TYPES OF CANCER CELLS

Answer 20

DEREGULATION OF RESTRICTION POINT DECISION MAKING MACHINERY

Question 21

WHAT IS THE IMPORTANCE OF S PHASE

Answer 21

1. DNA MUST BE REPLICATED ACCURATELY

2. DNA MUST BE COPIED ONCE

Question 22

WHAT IS LICENCING

Answer 22

IN G1 INACTIVE HELICASES ARE LOADED ONTO REPLICATION ORIGINS TO FORM A PRE RC WHICH ARE ACTIVATED IN S PHASE BY S PHASE CDKS

Question 23

IS THE CELL CYCLE ALWAYS THE SAME

Answer 23

NO, DIFFERENT CELL TYPES IE ESC AND FIBROBLASTS HAVE DIFFERENT CYCLIN PROFILES THAT ARE NOT FULLY UNDERSTOOD.