Unit 5: Cell Cycle

M phase

when cell division actually occurs (10% of time)

Interphase

prepares for cell division by growing, replicating DNA, checking for errors) with G1, Synthesis, G2 (90% of time)

When is cell division occurring?

M phase

Does the cell spend more time in M phase or Interphase?

Interphase

What are the three substages of Interphase?

G1 (gap 1) -> S (synthesis) -> G2 (gap 2)

List the substages of Interphase in the correct order. Which substage is the longest?

G1 (growth and metabolism)

What is the importance of Gap 1 phase of Interphase?

The cell is growing in size, making proteins and organelles, needed for formulating normal functioning, has many checkpoints

What is it called when a cell stays in Gap 1 indefinitely?

G0, cell exits cell cycle and does not proceed with DNA replication (can be temporary or permanent)

What is the importance of S phase of Interphase?

This is when DNA replication occurs, each chromosome gets duplicated, DNA in cells doubles to produce sister chromatids (identical copies of a single chromosome joined together in the centromere and separated during cell division)

What is meant by the term semi-conservative?

Each strand of DNA is conserved, even though the double helix is not

Primase:

synthesizes short RNA primers

DNA polymerase:

adds DNA nucleotides to the growing strand in the 5’ to 3’ direction

Helicase:

unwinds and separates the double-stranded DNA at the replication fork

Topoisomerase:

prevents the DNA from tangling or breaking

Ligase:

joins the Okazaki fragments on the lagging strand by forming covalent bonds between DNA fragments

DNA polymerase with exonuclease activity:

proofreads the newly synthesized DNA and removes incorrectly paired bases (3’ to 5’ exonuclease activity)

Single stranded binding proteins (SSBPs):

bind to and stabilize single-stranded DNA after it has been unwound by helicase

No primase:

no RNA primers would be made, DNA couldn’t start replication

No DNA polymerase:

nucleotides would not be added, replication would halt

No helicase:

the Dna double helix would not be unwound, replication fork would be blocked from proceeding

No topoisomerase:

DNA ahead of replication fork would become overwound and tangled, would stall or cause breakage

No ligase:

Okazaki fragments on the lagging strand would remain disconnected, lagging strand would be incomplete/unusable

No DNA polymerase with exonuclease activity (proofreading function):

errors during nucleotide pairing would go uncorrected, mutation rate would increase

No Single-Stranded Binding Proteins (SSBPs):

unwound DNA strands would reanneal or form secondary structures, replication would slow or stop

Telomeres

the ends of linear chromosomes that protect it from degradation

What enzyme can extend telomeres and in what kind of cells is it active?

Telomerase, active in germ cells, stem cells, cancer cells

What is the overall purpose of PCR?

To amplify a specific segment of DNA, generating millions of copies of a targeted region

 Is the entire chromosome copied or only a region?

Only a specific region

What is the purpose of primers in PCR?

short single-stranded DNA sequences that bind to the start and end of the target region and provide a free 3’-OH group for DNA polymerase to begin DNA synthesis

What must be added to the reaction mix? Why is Taq polymerase used instead of human polymerase?

PCR mix includes template DNA, primers, dNTPS (building blocks), buffer solution, Taq DNA polymerase (because it doesn’t denature at high temperatures unlike DNA polymerase)

When does DNA replication occur in the cell cycle? What is being produced and why is it being produced? 

Occurs in the S phase, exact copies of the entire DNA genome each chromosome is duplicated to form two identical sister chromatids, being produced to ensure when the cell divides each daughter cell has a full set of genetic material

 When does transcription occur in the cell cycle? What is being produced and why is it being produced? 

Occurs throughout interphase (mainly G1 & G2) , messenger RNA is produced (a single strand copy of a specific gene), made to carry genetic instructions

Describe the importance of Gap 2 phase of Interphase. What occurs during this substage of Interphase? 

Final growth and preparation top produce proteins and organelles, error check points and repair, may enter apoptosis

What kind of cell division do somatic cells undergo? Germ Line cells?

Somatic undergo mitosis

Germ undergo meiosis

What unique event occurs in prophase I of meiosis?

Homologous chromosomes pair up and undergo crossing over (genetic recombination) called synapsis

What are haploid versus diploid cells? Which one contains homologous chromosomes?

Diploid contain two sets of chromosomes and have homologous pairs

Haploid contains one set of chromosomes

Which type of cell division produces haploid cells from a diploid parent cell? Diploid cells from a diploid parent cell? 

Haploid cells from diploid parent -> Meiosis

Diploid cells from diploid parent -> Mitosis

When are haploid cells first produced from a diploid cell? 

After meiosis 1 when the diploid cell has divided into two daughter cells

Are the cells produced from mitosis genetically identical or different? Meiosis?

Mitosis: genetically identical

Meiosis: genetically different

When in the cell cycle does a cell have twice the amount of DNA as the cell in Gap 1 of Interphase?

During the S phase and G2 phase so it can be divided in the M phase

Would a daughter cell produced via mitosis have the same amount of DNA as the parent cell in Gap 1 phase of Interphase?

Yes

Would a daughter cell produced via meiosis have the same amount of DNA as the parent cell in Gap 1 phase of Interphase? If not, how would it differ?

No it would have half the amount because it produces haploid cells from a diploid parent

Describe how cells are able to progress from one stage of the cell cycle to the next. What must a cell receive to move from Gap 1 into S phase? 

Controlled by the cyclins and cyclin dependent kinases, pass through checkpoints, needs to receive a growth signal

Why is it important that the cell cycle is controlled? What role do the checkpoints play in this control?

The cell cycle must be tightly controlled to ensure accurate duplication and segregation of genetic material, preventing the accumulation of mutations and the development of diseases like cancer. Checkpoints act as surveillance mechanisms, pausing the cycle if problems like DNA damage or improper chromosome alignment are detected.

Which one promotes the cell cycle in response to a signal to undergo cell division?

Proto-oncogenes, normal genes that encode proteins which stimulate cell division in response to appropriate external signals (Cyclin D)

Which one halts the cell cycle in response to cellular stress and DNA damage?

Tumor suppressor proteins, monitor and regulate cell cycle they can pause or stop progression (p53)

Mutated or overactive proto-oncogenes are called ONCOGENES. How would these affect the cell cycle?

Oncogenes drive the cell cycle forward uncontrollably

How would non-functional tumor suppressor genes affect the cell cycle?

Tumor suppressors act as “brakes” to stop the cycle if problems occur, so without them, uncontrolled cell growth and division occur

Which type of tumor is associated with a high number of mutations – cancer or benign tumors or both? Why? 

Cancer has a higher number of mutations

Which type of tumor is associated with metastasis – cancer or benign tumors or both?

Cancer, metastasis is when cells break away from the original tumor and enter the bloodstream or lymphatic system to form new tumors

What is a mutagen? Why would it be associated with the development of tumors?

Mutagen is any agent that causes mutations in the DNA (radiation, tobacco, x-rays, chemicals, certain viruses)