Cell Cycle

Question 1

Why do cells divide?

Answer 1

1. Reproduction
2. Growth and Development
3. Tissue Renewal
4. Maintain SA:V Ratio

Question 2

Types of Cellular Division?

Answer 2

• asexual

– Mitosis

– Binary Fission

• sexual

– Meiosis

Question 3

~3 billion base pairs – ~20‐25,000 genes (only 2%)

Answer 3

only 2% encode protein, the rest are important for regulating gene expression

Question 4

• __________‐ the DNA of a cell

Answer 4

genome

Question 5

prokaryotes _________chromosome

Answer 5

single circular chromosomes

Question 6

eukaryotes

Answer 6

• Cells often contain two copies of each chromosome (homologous chromosomes)

Question 7

What is DNA? •

Answer 7

Composed of subunits called nucleotide • 3 components – nitrogenous base

– phosphate group

– sugar deoxyribose

• Double helix – Strands are complementary –

A pairs with T

G pairs with C

Question 8

what are chromosomes composed of?

Answer 8

Composed of chromatin

– DNA + proteins (histones)

Question 9

heterochromatin?

Answer 9

• Highly condensed
• Rarely expressed
• doesn’t encode lots of genes
• stays packed-this prevents machinery from getting in there and making an mrna copy

Question 10

euchchromatin?

Answer 10

• Condensed during division •

Expressed (actively transcribed)

machinery access and makes mrna copy

Question 11

– __________: condensed region of chromosome

Answer 11

centromere

Question 12

– __________: region of repetitive DNA sequences at end of chromosome

Answer 12

telomere

• every round of division- loose telomere, not a big deal-limited amount of time that cells can divide before loose dna when they reach a critical length
  1. cell stops or apoptosis

Question 13

– __________: disc‐shaped protein that spindle fibers attach to

Answer 13

kinetochore

-attachment when micro pulls chromatids on each side

Question 14

• Chromosomes are duplicated before ______

– Creates _______

– Held together at centromere

• During ______ the sister chromatids are pulled apart

Answer 14

division

sister chromatid

mitosis

once divide: chromosomes recoil so machinery can use information

Question 15

• Normal human chromosome count = 46

Answer 15

– 44 autosomes

– 2 sex chromosomes (X & Y)

Question 16

_______‐2 sets of chromosomes

• _______‐ 1 set of chromosomes

Answer 16

diploid

haploid (sperm and egg)

Question 17

__________ensures that when sperm fertilizes an egg—>46 chromosomes?

Answer 17

meiosis

Question 18

• _________ = atypical chromosome count

Answer 18

aneurploidy

• miscarriage in development
• down syndrome -extra 21st

Question 19

• _________ = having more than two paired sets of chromosomes – i.e. triploid, tetraploid

Answer 19

polyploidy

Question 20

why can aneuploidy and polyploidy be problematic?

Answer 20

• set window of amount of protein you should produce
• too much protein, too many directions

Question 21

T/F chromosome count determines complexity?

Answer 21

false

Question 22

Why Can’t Hybrid Animals/Plants Reproduce?

Answer 22

• It is possible for 2 different species to mate and produce offspring but… The offspring are almost always infertile…Why? • The parents each had a diff. # of chromosomes so the offspring has an uneven number – i.e. Horse (64) x Donkey (62)=Mule (63) • Plants are often able to reproduce-tries to make gametes can’t divide correctly, no viable sperm/egg

Question 23

Polyploidy in Plants

Answer 23

• Very common in plants (30‐80%) • Common mechanism of rapid speciation especially in angiosperms

cultivated- odd chromosomes-can’t produce viable gametes, white seeds: non functioning gametes

Question 24

Bacterial Binary Fission

how bacteria divides

Answer 24

form of asexual reproduction

1. cell elongates and DNA is replicated
2. cell wall and plasma membrane begin to divide
3. cross wall forms completely around the DNA
4. Cells separate

Question 25

Interphase

• __________: growth, protein synthesis, organelle synthesis

Answer 25

G1 (Gap1)

Question 26

Interphase

synthesis • __________

Answer 26

DNA is duplicated

Question 27

• __________: growth, synthesis of microtubules, cell cycle checkpoints

Answer 27

G2

Question 28

Majority of cells in the human body are here – Some cells can be called back (i.e. liver cells)

Quiescent or “resting” state, cells not dividing but are metabolically active.

Answer 28

• G0:

Question 29

Cells spend ___ of their time in interphase

Answer 29

90%

some never leave–might have mistake-apoptosis, be repaired, don’t pass on errors

Question 30

Mitosis

Answer 30

• nuclear division
• Followed by cytokinesis (division of organelles and cytoplasm)
• Produces 2 identical daughter cells

Question 32

What are the 5 stages of mitosis?

Answer 32

1. Prophase
2. Prometaphase
3. metaphase
4. anaphase
5. telophase

Question 33

what happens during prophase?

Answer 33

• Chromosomes begin to condense
• Mitotic spindle begins to form

– “machine” responsible for pulling apart the chromatids

– Composed of microtubules and other proteins

opposite sides to pull apart

analogy: yarn told to put in equal piles, bunch of dna is difficult to divide, if in balls of yarn, easier to divide, purpose of tightly packed chromosomes

-

Question 34

What happens during prometaphase?

Answer 34

Nuclear envelope disassembles- to unwrap

• Spindle fibers attach to kinetochores (prometaphase)-one on each side

Question 35

Metaphase

Answer 35

• Chromosomes align along the metaphase plate

– Occurs because of tug‐of‐war between the two poles

starting gate, before division need to be lined up-otherwise won’t evenly divide

Question 36

Anaphase

Answer 36

• Sister chromatids are cut apart

– Cohesion that hold them together cleaved by enzymes

• Sister chromosomes can now be pulled to opposite poles – Movement achieved through shortening of microtubules (depolymerize)

(

Question 37

Telophase

Answer 37

• Reversal of prophase events • Nuclear envelopes reform around DNA • Chromosomes unfold back into chromatin

(cell can get in to synthesize protein)

Question 38

Cytokinesis

Answer 38

• Division of cytoplasm • NOT a part of mitosis

– Begins during telophase (simultaneous)

• Animals – Cleavage furrow pinches off separated nuclei • Plants – New cell wall formed

– Golgi‐derived vesicles bring materials–to construct the cell wall

no rigid cell wall-pinch cell membrane in –2 cells

microfilaments-contract-squeeze cell in– 2 separate cells

Question 39

Cell Cycle Regulation

Answer 39

• Tight regulation is crucial for normal growth and development • Controlled by a system of signaling molecules which trigger and coordinate the events of the cell cycle • Multiple checkpoints make sure the cell is ready to proceed to the next step

Question 40

G1 Checkpoint

Answer 40

• restriction point ‐most important in mammals

point of no return-mediate g1 to s phase

replicate, committed to dividing

-

• If cell receives: – Green light: continues to s phase – Red light: exits cell cycle, enters Go: can stil enter cycle when it’s ready and it passes the checkpoint

metabolically active, makes more organelles, need to build cytoplasm, work on getting to the right size

Is the cell big enough, are conditions favorable, is there any DNA damage, etc.?

Question 41

Cell Cycle Clock

Answer 41

• 2 main regulatory molecules – cyclins
• Levels fluctuate cyclically (proteins)

– cyclin dependent kinase (add phosphate) • Present at constant concentrations but usually inactive

• Activated by attaching to cyclins

Question 42

Maturation‐Promoting Factor (MPF)

Protein dimer consisting of a ______ and ____

Answer 42

G2 checkpoint (G2 to M)

on switch so mitosis can move forward

controls transition from G2 to mitosis

made of: cyclin and cdk

• Targets include:

– Condensins

– Proteins involved in mitotic spindle formation

– Lamins

• Proteins involved in nuclear envelope assembly/breakdown

Question 43

without _____cdk isn’t active?

Answer 43

cyclin

Question 45

Anaphase Promoting Complex (APC) __________

Answer 45

M phase Checkpoint

(Metaphase to Anaphase) Complex of 11‐13 proteins that marks cell cycle proteins for degradation

Question 46

External Factors

Answer 46

• Growth Factors – i.e. Platelet‐

derived growth factor (PDGF)

• density dependent inhibition
• anchorage dependence