The Cell Cycle

Mitosis

• Somatic cell division

• Increase in somatic (body) cells

Meiosis

• Reproductive Cell Division

• Results in the production of gametes

Interphase

Which stage has three phases?

• G1

• S

• G2

Eukaryotic

Prokaryotic or eukaryotic?

Cell cycle includes two phases: Interphase and Mitotic phase

Prophase, Metaphase, Anaphase, Telophase

What are the stages of mitosis?

Mitosis

Mitosis or Meiosis?

• allows cells to pass on exact copies of their DNA

bacterium

Which of the following organisms does NOT reproduce cells by mitosis and cytokinesis?

a.) cow

b.) bacterium

c.) mushrom

d.) cockroach

e.) banana tree

Production of gametes

Which of the following is NOT a function of mitosis in a multicellular organism?

a.) Growth from a fertilized egg

b.) Replacement of damage cells

c.) Maintenance of tissues

d.) Production of gametes

G1 phase

• first stage of interphase in the cell cycle

• cell is very active metabolically

• cell produces and accumulates proteins and building blocks needed for DNA replication

G1

Which phase in interphase:

stores energy and resources required to replicate each chromosome in the nucleus

S phase

• DNA is replicated

• identical sister chromatids produces and remain attached at the centromere

S phase

Which phase of interphase is:

the centromere duplicated to form the mitotic spindle

S phase

Which phase of interphase is:

the mitotic spindle formed

mitotic spindle

removes chromsomes during mitosis

histones; non-histones

compact eukaryotic DNA

chromatin

The complex of DNA and protein is called

Telomeres

• end caps of chromosomes

• essential for stability

Centromeres

• Center part of chromosome

• Attachment site of two double helices

G2 phase

• Final stage of interphase before mitosis

• the cell replenishes energy and synthesizes proteins needed for chromosome movement during mitosis

• some organelles are duplicated, and parts of the cytoskeleton are dismantled

G2 phase

Which phase of interphase is:

Final growth and preparation for mitosis

G2 phase

Which phase of interphase is:

Some organelles are duplicated

G2 phase

Which phase of interphase is:

Cells replenishes energy and synthesizes proteins

M phase

Duplicated chromosomes are aligned, separated, and distributed into two identical daughter cells

karyokinesis

• first part of the mitotic (M) phase

• division of the nucleus

• chromosomes are organized and separated into two nuclei

cytokinesis

• second part of the mitotic (M) phase

• the physical division of the cytoplasm, forming two separate daughter cells

T

T or F?

Cells use cell-cycle checkpoints—control points where progression can pause until conditions are correct.

T

T or F?

Daughter cells must be the exact duplicates of the plarent cell

mutations

Errors in chromosome replication or distribution can cause _____ that pass to future cells.

G1; G2/M; metaphase

Major checkpoints occur at the end of ___, at the ___/___ transition, and during ______.

promote

Intracellular molecules that ____ are positive regulation.

Positive

Negative or positive regulators?

Cyclins and cyclin-dependent kinases (Cdks)

Cyclin

_______ levels fluctuate predictable throughout the cell cycle.

degraded

After a stage is completed, active cyclins are _____ by cytoplasmic enzymes to ensure proper progression.

cyclin; phosphorylation

A Cdk becomes active only after binding to a ______ and receiving an activating ________.

cyclin

The ______ component helps guide the Cdk to the correct target proteins for phosphorylation.

cyclin-Cdk

The _____–___ complex phosphorylates specific target proteins to drive progression through the cell cycle.

Cdks

enzymes that phosphorylate other proteins, activating them to advance the cell to the next phase

cyclin

Fluctuating _____ concentrations determine when specific Cdk/cyclin complexes form and regulate different checkpoints.

phosphorylation

Cdk/cyclin complexes require ________ at specific sites to become fully active.

Cyclins

only regulate the cell cycle when bound to cyclin-dependent kinases (Cdks), forming an active Cdk/cyclin complex.

Mitosis

An M-Cdk would trigger:

a.) mitosis

b.) S phase

Ubiquitylation

What modifies cyclin for destruction?

APC/C

Which complex adds ubiquitin to cyclin?

activates Cdk

What does cyclin do for Cdk?

inactive

When cyclin is destroyed/lost, Cdk becomes ______.

proteasomes

Ubiquitylated cyclin is degraded in _______.

kinases

Inhibitory _______ inactivate Cyclin-Cdkcomplexes

phosphatases

Activatory ________ activate Cyclin-Cdkcomplexes

Proto-oncogenes

normal genes that drive cell-cycle progression; when mutated, they become oncogenes that can push cells through checkpoints inappropriately.

positive

Hyperactive ________ regulators

• let damaged cells divide

• increase the chance of further harmful mutations

• e.g., Cdk without cyclin

Tumor suppressors

• act as brakes on the cell cycle

• mutations remove these checkpoints, allowing uncontrolled division

• e.g., Rb, p53, p21

p27

Which negative regulator?

Cell is prevented from progressing from G1 to S phase when ____ binds to an already active cyclin-Cdk complex.

• blocks the Cdk’s ability to phosphorylate its target proteins

Rb

• a key negative regulator at the G1 checkpoint

• monitors cell size and controls progression to S phase.

Rb

In its active (dephosphorylated) state:

____ binds transcription factors like E2F, blocking the production of proteins needed for the G1/S transition.

phosphorylated; inactivated

As the cell grows, Rb becomes _______ and ________.

DNA damage

activates protein kinases that stabilize and activate p53, allowing it to accumulate in the cell.

p21

Activated p53 promotes transcription of ___, a Cdk inhibitor protein.

p21

inhibits G1/S and S Cdks, preventing progression into S phase and arresting the cell cycle in G1

Cdc6; ORC

What loads helicase?C

S phase

When does replication start?

The activation of S-Cdk helps prevent the onset of M phase

Which of the following is false?

a.) The activation of S-Cdk initiates DNA replication
b.) DNA replication occurs only in S phase

c.) The activation of S-Cdk helps prevent DNA replication from occurring more than once during each cycle

d.) The activation of S-Cdk helps prevent the onset of M phase

The duplicated chromosomes are correctly aligned on the mitotic spindle

The cell cycle system initiates chromosome segregation only after which of the following has occurred?

a.) DNA has been completely replicated and the chromosomes have been decondensed

b.) Cytokinesis is complete

c.) M phase is complete

d.) The duplicated chromosomes are correctly aligned on the mitotic spindle

The kinase activity of the Cdk subunit increases at different stage of the cycle

How do cyclin-Cdk complexes trigger different stages of the cell cycle?

a.) The concentration of the Cdk subunit increases at different stages of the cycle

b.) The Cdk subunits are degraded at different stages of the cycle

c.) The kinase activity of the Cdk subunit increases at different stage of the cycle

d.) All the above

M phase-cytokinesis

Which of the following correctly matches a phase of the eukaryotic cell cycle with an event that takes place in that phase?

a.) S phase-preparation for entry into cell cycle.

b.) G1 phase-DNA synthesis.

c.) G2 phase-mitosis.

d.) M phase-cytokinesis.

It ensures that the M phase is completed before cytokinesis occurs

Which of the following statements about the cell cycle control system is NOT true?

a.) It ensures that the environment is favorable for the cell to initiate DNA replication.

b.) It ensures all chromosomes are attached to the mitotic spindle before the chromosomes are segregated

c.)d.It ensures that all the DNA is replicated before the M phase begins

d. ) It ensures that the M phase is completed before cytokinesis occurs.