Development Test: What to Study

Here’s what you need to study in order to d e m o n st ra t e yo u r u n d e rst a n d in g o f g e n e t ic s :● DNA & RNA St ru c t u re

● Sc ie n t is t in vovle d in Discove ry● DNA Re p lica t ion

● En zym e s In vo lve d● Ce ll Cyc le

○ P h a se s

○ St ru c t u re s a n d Fu n c t ion s● Ce ll Cyc le Re g u la t ion

● Ch e ckp o in t s

● P 53 Ge n e

● Meiosis ○ Where it happens○ Why?○ What kind of cells it

produces○ Ploidy of cells

produced○ Difference between

meiosis and mitosis○ What happens when

meiosis goes wrong

Nucleic Acids● Kn o w :

○ Mo n o m e r o f n u c le ic a c id s

○ Typ e s o f NA’s○ Ro le in livin g syst e m s,

e xa m p le s

DNA Structure

DNA is a nucleic acid that stores genetic information. It has directionality (3’ -5’) due to orientation of the carbons on the sugar

DNA ReplicationDNA re p lica t io n o ccu rs d u rin g t h e S phase of the cell cycle

It begins with an origin of replication

Due to the antiparallel nature of the molecule, there are two strands:

Leading

Lagging

DNA ReplicationOn t h e Leading strand , DNA polymerase binds to the 5’ end and builds a new DNA strand complementary to the parent strand. This new strand runs in the 5’ to 3’ direction. The replication on this strand is continuous and goes INTO the replication fork.

DNA ReplicationOn t h e Lagging strand , DNA replication must occur in the 5’ to 3’ direction but has to happen BACKWARDS since the lagging strand is oriented 3’ to 5’.

Okazaki fragmentsmust be created on the lagging strand for this reason. Each fragment has an RNA primer that

Phases of the Cell Cycle

Phases of the Cell Cycle● The mitoticphase alternates with interphase:

G1→ S → G2 → mitosis → cytokinesis● Interphase (90 % of cell cycle)

▪ G1 Phase: cell grows and carries out normal functions▪ S Phase: duplicates chromosomes▪ G2 Phase: prepares for cell division

● M Phase (mitotic)▪ Mitosis: nucleus divides (PMAT)▪ Cytokinesis: cytoplasm divides

Mitosis : Prophase → Metaph ase →An aph ase → Teloph ase

PMAT not IPMAT!

Cytokinesis in animal vs. plant cells

Checkpoint Control System▪ Checkpoints

◆ Cell cycle controlled by STOP & GO chemical signals at critical points

◆ Signals indicate if key cellular processes have been completed correctly▪ Ext e rn a l- Grow t h Fa c t o rs▪ In t e rn a l- P rom ot in g Fa c t o rs

• Cyc lin s• Cyc lin De p e n d e n t Kin a se s

3 Major Checkpoints “Ask” Critical Questions

G1/S◆Can DNA synthesis begin?

G2/M◆Has DNA synthesis been completed

correctly?◆Commitment to Mitosis

Spindle Checkpoint◆Are all chromosomes attached to

spindle?◆can sister chromatids separate correctly?

“Go-ahead” Protein signals▪ Protein signals that promote cell growth & division

◆ External “Go -a h e a d ”Signals▪ “Growth Factors”

◆ In t e rn a l “Go -a h e a d ”Sig n a ls▪ “P ro m o t in g Fa c t o rs”

▪ Primary Mechanism of Control◆ P hosphorylation-

▪ a d d s p h o sp h a t e g ro u p s t o t a rg e t▪ Kinase- a p h o sp h oryla t in g e n zym e▪ either activates or inactivates cell signals

“Go-ahead” Protein signals▪ Protein signals that promote cell growth & division

◆ External “Go -a h e a d ”Signals▪ “Growth Factors”

◆ In t e rn a l “Go -a h e a d ”Sig n a ls▪ “P ro m o t in g Fa c t o rs”

▪ Primary Mechanism of Control◆ P hosphorylation-

▪ a d d s p h o sp h a t e g ro u p s t o t a rg e t▪ Kinase- a p h o sp h oryla t in g e n zym e▪ either activates or inactivates cell signals

Promoting Factors▪ In t e rn a l P ro t e in Sig n a ls

◆ cyclins▪ regulatory proteins▪ levels cycle in the cell

◆Cdks▪ cyclin-dependent kinases▪ phosphorylates cellular proteins

• activates or inactivates proteins

◆Cdk-cyclin complex▪ triggers passage through different stages of cell cycle▪ e x. Ma t u ra t io n P ro m o t in g Fa c t o r

activated Cdk

inactivated Cdk

Cyclin & Cyclin-dependent kinases▪ CDKs & cyclin drive cell from

one phase to next in cell cycle

◆proper regulation of cell cycle is so key to life that the genes for these regulatory proteins have been highly conservedthrough evolution

◆ the genes are basically the same in yeast, insects, plants & animals (including humans)

Specific Cyclins and CDKs promote progression t h rou g h sp e c ific p h a se s

Cdk / G1

cyclin

Cdk / G2cyclin (MPF)G2

S

G1

CM

G2 / M checkpoint

G1 / S checkpoint

APC

Active Inactive

ActiveInactiveInactive

Active

mitosiscytokinesis

MPF = Mitosis Promoting FactorAPC = Anaphase Promoting Complex

• Replication completed• DNA integrity

Chromosomes attached at metaphase plate

Spindle checkpoint

• Growth factors• Nutritional state of cell• Size of cell

Growth Factors and Cancer▪ Growth factors can create cancers

◆ proto-oncogenes▪ normally activates cell division

• growth factor genes • become oncogenes (cancer-causing) when mutated

▪ if switched “ON” can cause cancer▪ example: RAS (activates cyclins)

◆ tumor-suppressor genes▪ normally inhibits cell division▪ if switched “OFF” can cause cancer▪ example: p53

Cancer & Cell Growth▪ Cancer is essentially a failure

of cell division control◆ unrestrained, uncontrolled cell growth

▪ What control is lost?◆ lose checkpoint stops◆ gene p53 plays a key role in G1/S restriction point

▪ p53 protein halts cell division if it detects damaged DNA • options:

■ stimulates repair enzymes to fix DNA ■ forces cell into G0 resting stage■ keeps cell in G1 arrest ■ causes apoptosis of damaged cell

▪ ALL cancers have to shut down p53 activity

p53 discovered at Stony Brook by Dr. Arnold Levine

p53 is theCell CycleEnforcer

DNA damage is causedby heat, radiation, or chemicals.

p53 allows cellswith repairedDNA to divide.

Step 1

DNA damage iscaused by heat,radiation, or chemicals.

Step 1 Step 2

Damaged cells continue to divide.If other damage accumulates, thecell can turn cancerous.

Step 3p53 triggers the destruction of cells damaged beyond repair.

ABNORMAL p53

NORMAL p53

abnormalp53 protein

cancercellStep 3The p53 protein fails to stop

cell division and repair DNA.Cell divides without repair todamaged DNA.

Cell division stops, and p53 triggers enzymes to repair damaged region.

Step 2

DNA repair enzymep53protein p53

protein

p53 — master tumor suppressor gene

Meiosis● Re sp on sib le fo r

p rod u c t ion o f g a m e t e s

● P rod u ce s h a p lo id ce lls

● Also kn ow n a s re d u c t ion d ivis ion

Meiosis: Homologous Chromosomes

● Hom olog ou s p a irs h a ve t h e sa m e s ize , sa m e le n g t h , h a ve t h e sa m e g e n e s in t h e sa m e o rd e r b u t h a ve d iffe re n t a lle le s

Overview of Major Events in Meiosis Meiosis I: Synapsis, Crossover, Independent Assortment and separation of homologous pairs Meiosis II: Separation of sister chromatids and segregation of alleles

Crossing Over: A Mechanism for Creating Ge n e t ic Va rie t y ● Crossove r occu rs

a t P rop h a se I● P ie ce s o f NON-

SISTER ch rom a t id s e xch a n g e DNA w it h on e a n o t h e r t o c re a t e re com b in a n t ch rom osom e s

Cell Differentiation Demands Co o rd in a t io nD ifferent tissues & organs develop, grow, and repair at different rates

◆ Th is is c ritical for normal growth, development & maintenance▪ Timing of cell division must be rig h t▪ Rates of cell division are uniqu e▪ Not all cells can have the

same Cell Cycle

G2

S G1

Mmetaphase

prophaseanaphase

telophase

interphase (G1, S, G2phases)mitosis (M)cytokinesis (C)

C

▪ Embryos◆ cell cycle < 20 minute

▪ Skin Cells◆ D ivide frequently throughout life◆ 12-24 hours cycle

▪ Liver Cells◆ Retain ability to divide, but keep it in reserve◆ D ivide once every year or two

▪ Mature Nerve Cells & Muscle Cells◆ Do not divide at all after maturity◆ P ermanently in G0

Frequency of Cell D ivision Varies by Type