Chapter 5: Cell Cycle and Cell Division Flashcards
What is the primary result of mitosis?
Two genetically identical daughter nuclei.
What process follows mitosis in cell division?
Cytokinesis.
During which phase of the cell cycle does DNA replication occur?
S phase.
What major event occurs during the G1 phase?
Cell growth.
What is the state of DNA throughout interphase?
Chromatin.
What is the role of microtubules in the G2 phase?
Begin forming kinetochores for mitotic processes.
How many chromosomes are present in a typical human cell?
46 chromosomes.
What is a chromatid?
One of two identical DNA structures in a chromosome.
What is the structure that joins two chromatids together?
Centromere.
What type of molecule primarily makes up chromosomes?
DNA and histone proteins.
What is chromatin?
Loosely coiled DNA and histones.
What is the tightly coiled form of DNA called?
Chromosome.
What is the visible
most condensed form of DNA?
What is the function of kinetochores during mitosis?
Bind DNA to microtubules at the centromere.
When do kinetochores begin construction?
S phase.
Do plant cells require centrosomes for mitosis?
No.
What is the biological significance of mitosis in growth?
Produces genetically identical cells for multicellular growth.
How does mitosis contribute to tissue repair?
Replaces dead cells with identical ones.
What role does mitosis play in asexual reproduction?
Produces offspring genetically identical to the parent.
Which immune cells clone during the immune response via mitosis?
B- and T-lymphocytes.
What happens to DNA during interphase?
It replicates.
What happens to DNA at the start of mitosis?
It condenses into chromosomes.
What happens during cytokinesis in animal cells?
The cell membrane pinches to divide the cytoplasm.
How does cytokinesis differ in plant cells?
A cell plate forms to divide the cytoplasm.
What phase of the cell cycle involves nuclear division?
Mitosis.
What are telomeres?
Protective caps on the ends of chromosomes.
How do stem cells relate to mitosis?
They divide to produce specialized cells.
What is the relationship between cancer and mitosis?
Uncontrolled mitosis leads to tumor growth.
What key process occurs in metaphase of mitosis?
Chromosomes align at the cell equator.
What separates chromatids during anaphase?
Spindle fibers.
What is the key feature of prophase in mitosis?
Chromosomes become visible
What forms during telophase of mitosis?
Two new nuclear envelopes.
What structure pulls chromosomes apart during mitosis?
Spindle fibers.
What is a nucleosome?
DNA wrapped around histones.
Why are daughter cells genetically identical after mitosis?
Each receives one identical chromatid.
What type of reproduction is mitosis essential for in unicellular organisms?
Asexual reproduction.
What stage of mitosis involves the spindle fibers fully attaching to kinetochores?
Metaphase.
What happens to chromatids during anaphase?
They are pulled to opposite poles of the cell.
What distinguishes plant cell cytokinesis?
Formation of a cell plate.
How do histones assist DNA organization?
They help coil DNA into nucleosomes.
What is the smallest phase in terms of cell size?
Beginning of G1.
What is the primary molecule of inheritance?
DNA.
What kind of cells does mitosis produce in terms of ploidy?
Diploid.
What event ensures equal DNA distribution during mitosis?
Chromatid separation.
Which phase of mitosis involves the reformation of nuclear membranes?
Telophase.
How do chromosomes differ in metaphase versus prophase?
In metaphase
What is the significance of centrosomes in animal mitosis?
Organize spindle fibers.
What is a key structural change in chromosomes during supercoiling?
They become tightly packed and visible.
Why is mitosis critical for the immune response?
Cloning of immune cells.
What occurs at the centromere during mitosis?
Attachment of spindle fibers.
What is the role of spindle fibers in metaphase?
Align chromosomes at the equator.
What is the function of histones in chromatin?
Support and organize DNA.
How are cells in the G1 phase characterized in size?
Smallest size.
What triggers cytokinesis after mitosis?
Division of the cytoplasm.
In which phase are organelles increasing in number?
G2 phase.
What is the function of the cell plate in plants?
Divides the cytoplasm.
What happens to the nuclear envelope during prophase?
It breaks down.
Which phase follows DNA replication?
G2 phase.
What role do genes play in chromosomes?
Carry instructions for traits.
What is the most condensed form of DNA?
Chromosome.
What are 2 major phases in a cell’s life?
Growth (Interphase) and Division (M Phase)
What does G in G1/G2 mean?
Gap
Products of mitosis?
2 genetically identical daughter cells
What are sister chromatids?
2 identical chromatids of a chromosome
Why must chromosomes uncoil sometime?
Chromosome is too packed
=> Inaccessible, enzymes can’t bind to
=> Can’t function
When are chromosomes uncoiled?
Start of interphase to end of G2.
Why do chromosomes only coil during M phase?
During mitosis, the cell doesn’t need to ‘read information’ on DNA anymore
=> Coil into compact form for easier transport
Why do most differentiated cells (e.g. nerve cells, cardiac muscle cells) don’t go beyond G0?
- Preserve complex and specialized function (more important)
- Reduce risks of error during division
When does the nuclear envelope disappear during mitosis?
Late prophase (~prometaphase).
Difference between prophase and prometaphase?
Prometaphase: spindle fibers actively connects to chromosomes at kinetochores
-> Transition between prophase and metaphase.
What is cytokinesis?
Division of cytoplasm right after mitosis/meiosis.
How do spindles (microtubules) pull chromosomes to opposite ends?
Attach to kinetochores then shorten at both ends
When is a chromosome most visible?
Metaphase.
Why doesn’t plant’s mitosis require centrosomes?
- Cell walls are too strong
=> Can’t cut through during cytokinesis - Use MTOC to form spindles instead of centrosomes
Microtuble Organizing Center
What is animal’s contractile ring during cytokinesis made of?
Actin & myosin
Proteins involved in contraction
Key differences between cytokinesis in plants and animals?
Animal:
Forms contractile ring around cell
-> Tightens, pull membrane inward
-> Forms cleavage furrow => Pinched in 2
Plant:
Vesicles containing cell walls materials gather at center
-> Form cell plate
-> Extend outward to form new wall => 2 new cells
Biological significance of mitosis?
- Growth
- Cell replacement (regeneration)
- Asexual reproduction (binary fission)
- Immune response (cloning of B- and T-lymphocytes)
How does cytokinesis occur in prokaryotes?
FtsZ proteins assemble Z ring
-> forms septum
-> make new cell walls
What is the significance of telomeres?
Protective end of chromosomes, like aglets
-> Longer DNA so D pol won’t miss important parts + won’t cut wrong parts
-> Prevent chromosomes from sticking together
Structure of telomeres?
Repeating DNA sequences
-> TTAGGG repeated thousands of times
How do telomeres change after each division?
It shortens.
because D Pol doesn’t cut exactly at the very end
What is used to prevent telomeres from completely disappearing after divisions?
Telomerase adds bases back in
-> Repair
-> Prevent aging (telomeres too short => wrong repli. => cells die)
only in eukaryotes
What does the cell do during interphase?
Grow to normal size after division, carry out functions (transcript, translate, etc.)
What does the cell do during S phase?
Replicates DNA
after cell received signal to divide
What does the cell do during G1 phase?
Grow; make RNA, proteins, enzymes
What does the cell do during G2 phase:
- Grow
- Check replicated DNA
- Repair errors
- Prepare for M (produce more tubulins -> microtubules -> spindles)
What does the cell do during M phase?
- Growth stops
- Nuclear division (karyokinesis)
- Cytokinesis
How many threshold (checkpoint) are there during the cell cycle?
3:
* G1 checkpoint (restriction point)
* G2/M checkpoint
* M checkpoint (spindle checkpoint)
What does the G1 do?
At the end of G1, check for sufficient size + nutrients and undamaged DNA
What happens if detect errors at G1 cp.?
Cells enter G0 - resting state for delayed division
What does the G2/M cp. do?
End of G2, before M: confirms completion of DNA replication, undamaged
What happens if errors are detected at the G2/M cp.?
Stop to repair
What does the M checkpoint do?
Happens at metaphase
-> Ensure all chromosomes are properly attached to spindles and well-aligned.
What happens if cell can’t pass through M checkpoint?
Stop dividing, apoptosis
-> Prevents aneuploidy
How does the cell move from 1 phase to another in the cell cycle?
Groups of proteins called cyclins bind to CDKs
=> Activate enzymatic functions
=> Move through phase
CDK: cyclin-dependent kinases
e.g. G1 cyclin at G1 cp. trigger DNA replication -> transit to S phase
Why must the cell cycle be regulated?
Ensure cells only divide when needed
Detect and repair errors, prevent mutations and cancer
When is cell cycle regulated?
At internal checkpoints:
* Stop cycle when conditions are unfavorable
* Resume when fixed, apoptosis if can’t fix
Trigger by external events
* Both initiation and inhibition
e.g. nearby cell death, high/low levels of HGH
HGH: human growth hormones
What are 2 types of regulation at internal checkpoints?
- Positive regulation: promotes to next phase
- Negative regulation: halts cycle
How is cell cycle regulation related to concentration of cyclin?
Many proteins that regulate cell cycle positively are made of cyclin and CDKs
e.g. MPF - M-phase promoting factor
Cyclin isn’t always present in cells
Cyclin activate CDKs for phosphorylation to advance to next phase
What are the 3 most researched enzymes used for negative cell cycle regulation?
Rb, p53, p21
When does p53 act?
When DNA is damaged:
* either: stop cycle, recruit enzymes to repair
* or: trigger apoptosis
How can p53 stop cell cycle?
p53 concentration increases drag along concentration of p21.
p21 inhibits cyclin/CDK complexes => can’t advance
What does Rb in Rb enzyme stand for?
Retinoblastoma protein.
What does Rb do?
Monitors cell size, regulate cell cycle in accordance to cell size
Mechanism of Rb?
Normal (active state): dephosphorylated
* Binds to transcription factors (mostly E2F)
* Blocks production of protein needed for G1/S transition
When cell grows in size:
* Rb is gradually phosphorylated
* Inactivated -> Releases E2F so cells can advance
When E2F is released, posi. reg. is turned on and and nega. reg. is off
Nature of cancer?
Uncontrolled cell growth
When does cancer occur?
Mistakes in DNA x2
-> Faulty proteins that were important in cell reprod.
-> Errors in regulators (delayed binding of cyclin-CDK, etc.)
Deactivated regulators => Evade apoptosis
Affected by carcinogens (as mutagens) => Damage cells
carcinogens: factors causing cancer
mutagens: factors causing mutations
Result of cancer?
Tumor, either benign or malignant
What is the difference between benign and malignant tumor?
Benign tumors don’t metastasize, malignant tumors do.
How does metastasis occur?
Primary tumor changes in cell chemistry
=> Encourages formation of capillaries
* Grow into tumors, provide nutrients => Tumors grow
* Route for malignant cells to travel to other parts => Start secondary tumors
What are 2 types of genes involved in regulating cell cycle?
Proto-oncogenes and tumor-suppressor genes
How does proto-oncogenes regulate cell cycle?
Code for positive cell cycle regulators
What will proto-oncogenes turn into if mutated?
Oncogenes.
How do oncogenes cause cancer?
Boost cell cycle progression rate
=> Uncontrollable cell division (rare)
Do oncogenes cause damage regularly?
No, most of the time the damage done by oncogene is fixed/removed.
Example of damaged done by oncogene?
Mutation allowing CDK to become activated without cyclin
=> Push past checkpoint before fulfilling requirements
=> Cancerous cells
=> Tumors (if divided)
What do tumor-suppressor genes do?
Code for negative cell cycle regulators
=> Stop cell division.
Examples of tumor-suppressor genes?
Rb, p53, p21.
What if tumor-suppressor genes are mutated?
Becomes non-functional:
* Can’t fix damaged DNA
* Can’t trigger apoptosis
* Can’t produce p21 to block CDK activation => bypass cp. without sufficient quality
=> Daughter cells contain mutations and broken TSG
=> Tumor growth if propagates
