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BIO111 Cell Biology > Lecture 11 & 12 Cell cycle and cell division > Flashcards

Lecture 11 & 12 Cell cycle and cell division Flashcards

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1
Q

Why is cell division important?

A

-Continuity of life
• Passes genetic information to the next generation
• Universal – unicellular to multicellular
• Long, complex series of cell divisions required
• Replace cells that die

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2
Q

How is cell division acheived?

A 
• AIM: To produce two genetically identical daughter cells
• Replication of DNA in each chromosome
• Duplicate organelles
• Two complete copies accurately
distributed between daughter
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3
Q

What is mitosis?

A

Mitosis:

  • Asexual reproduction
  • Diploid (two complete chromosome sets)
  • Homologous copies
  • Daughter cells are genetically identical
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4
Q

After which phase in the cell cycle does mitosis come?

A
  • After interphase (resting phase)

- interphase made up of G1, S, G2

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5
Q

What happens in the G1 phase of the cell cycle?

A
  • AIM: Recover from M Prepare for S phase
  • Gap/Growth Phase 1
  • General DNA checking/repair
  • Synthesis of RNA and protein
  • Generation of new organelles
  • Increase in cell size
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6
Q

What happens in S phase of cell cycle?

A

• AIM: To replicate genome
• Synthesis phase
• Chromosome duplication
(DNA= histones and chromatin = chromosome)

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7
Q

What are cohesins?

A

• A large protein complex
• Deposited at many positions along the sister
chromatids during DNA replication
• Holds sister chromatids together

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8
Q

What is karyotyping?

A

-occurs doing metaphase
• Species variation: Humans – 23 pairs of homologous chromosomes (2n)
• shows Size, shape, position of centromere
• Alternations could lead to genetic disorders

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9
Q

What happens in the G2 phase of the cell cycle?

A
  • AIM: To prepare for mitosis
  • Gap/Growth Phase 2
  • Second round of DNA proofreading
  • RNA and protein synthesis resumes
  • Cell confirms the number of chromosomes and the organelles present
  • Microtubule synthesis
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10
Q

What happens during the M phase of the cell cycle?

A 
• AIM: Cell division
• Mitosis
• Divide sister chromatids
• Divide the nucleus
• Division of the cytoplasm (Cytokinesis)
Mitosis:
• Asexual reproduction
• Diploid (two complete chromosome sets)
• Homologous copies
• Daughter cells are genetically identical
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11
Q

What are the phases of mitosis?

A
  • prophase
  • prometaphase
  • metaphase
  • anaphase
  • telophase
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12
Q

What happens in Prophase?

A

• Chromosomes replicated in S phase condense (two sister chromatids)
• Mitotic spindle assemble between the two centrosomes:
+ Centrosomes – organelle, microtubule organising centre
+ Centrosome = centrioles + microtubules

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13
Q

What happens in Prometaphase?

A
  • Nuclear Envelope breaks down
  • Chromosomes attach to spindle microtubules via kinetochores (Cohesin laid down during S phase are removed)
  • Chromosomes undergo active movement
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14
Q

What happens during metaphase?

A

• Chromosomes are aligned at the equator of the spindle, midway between the spindle poles
• The kinetochore microtubules attach sister chromatids to opposite poles
of the spindle

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15
Q

What happens during anaphase?

A
  • Sister chromatids synchronously separate to form two daughter chromosomes
  • Each is pulled slowly towards the spindle
  • Kinetochore microtubules get shorter, spindle poles move apart to complete chromosome segregation
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16
Q

What happens during telophase?

A
  • Two sets of daughter chromosomes arrive at the spindle poles and decondense
  • New nuclear envelope reassembles around each set of chromosomes
  • Two nuclei are formed marking the end of mitosis
17
Q

What happens during cytokinesis?

A
  • Cytokinesis starts in late anaphase (plants are different to animals)
  • Contractile ring of actin and myosin filaments pinches the cell in two
  • Two daughter cells are created each with one nucleus and three decondensed chromosomes
18
Q

How is cytokinesis different in plants?

A
  • Plant cells cannot form a contractile ring
  • Assemble a plasma membrane and cell wall between two daughter nuclei
  • Cell Plate
19
Q

How has our understanding of the cell cycle progressed?

A
  • Model organisms
  • Unicellular
  • Multicellular
20
Q

What is binary fission?

A
  • Unicellular organisms
  • Mitosis (asexual reproduction)
  • Cell elongates and DNA is replicated
  • Cross wall forms
  • Identical clone daughter cells
  • Adapt to new conditions?(only sometimes)
21
Q

How is yeast used to study the cell cycle?

A

Regular yeasts:
• Fission yeast S. pombe has a typical eukaryotic cell cycle
• Rod shape grows by end elongation
• Exhibits G1, S, G2 and M phases
• The budding yeast S. cerevisiae has a different cell cycle
• G1, S and M phases, but does not have G2 phase
Mutant yeasts:
• Rapid reproduction, small genome
• Haploid (single gene copy)
• Easy genetic manipulation: deletion, replacement, alteration
• Discovery of cell-division-cycle genes (cdc genes)
-CDC sensitive mutants:
• Search for cdc genes – ‘cell cycle arrest’ at a specific phase
• Conditional temperature sensitive mutation
• Continue through cell cycle until inactivation gene required
• Uniform cell cycle arrest

22
Q

How are embryonic frog cells used to help further our understanding of multicellular cell cycle?

A
  • Important model for studying cell cycle
  • Large cells (1mm diameter)
  • Easy to inject test samples
  • Large cytosol volume (contains proteins involved in cell cycle)
  • Rapid sequence of cell divisions - CLEAVAGE DIVISIONS
  • Divided into S and M phases (15 mins each)
  • No detectable G1 or G2 phases
23
Q

How is the role for chemical signals in the cell cycle tested for?

A
  • Cell fusion experiments
  • Fuse S phase and G1 phase
  • DNA synthesis initiates in G1 nucleus
  • Substance in S phase cell responsible? (perhaps)
  • Fuse M phase nucleus with G1 (interphase) cell
  • Cell G1 cell immediately enters mitosis
  • Chromosome not replicated (no S phase)
  • But, spindle formed, chromatin condensed and nuclear envelope breakdown occurs
  • Condensed chromosome unduplicated
24
Q

What are the key transition points in the cell cycle?

A
  • G2=M transition
  • Metaphase=Anaphase transition
  • G1= restriction point (if it doesnt go on to duplicate)
25
Q

What are the controllers of transition points?

A

• Cyclin dependant kinase (CDKs) – inactive (anaphase promoting complex APC)
• Cyclins:
+ Four types – G1, S, G2 and M
+ Synthesised at specific cell cycle phases
+ Protected from degradation and accumulate
+ Cyclically degraded
• Cyclins/CDK complex (regulate transitions)
• MPF (maturation promoting factor)
• GO signal for transition points

26
Q

How can CDK inhibitors (CDKIs) suppress CDK activity?

A
  • Tumour suppressor genes
  • Block CDK phosphorylation activity
  • Arrest cells – frequently at G1 phase (G0)
27
Q

For what reason would a transition be blocked?

A 
-restriction point (G1)
\+Growth factors, nutrients
\+Cell Size
\+DNA Damage
-G2=M transition
\+Cell size
\+DNA Damage
\+DNA replication
-Metaphase-Anaphase transition
\+Chromosome attachments to spindle
28
Q

What are some extrinsic factors that can affect the cell cycle?

A
  • Mitogens
  • Platelet-derived growth factor
  • Anchorage-dependent growth
  • Density-dependent growth
  • Cell cycle blocked even in presence of growth factors
29
Q

What is meiosis?

A

Sexual reproduction:
• HAPLOID cells (n) – carry only a single copy of the chromosome
• Gametes (eggs, sperm) are haploid cells
• When an egg and sperm fuse a DIPLOID zygote is formed
• DIPLOID CELL (2n) – two slightly different copies of the same chromosome one from each parent
• Genomes of two parents mix to generate
genetically distinct offspring

30
Q

Describe the process of Meiosis?

A

• Starts with a DIPLOID zygote – two slightly different copies of the same chromosome one from each parent
• Meiosis generates HAPLOID daughter cells – carry only a single copy of the chromosome
• Reduces chromosome number
• Often differentiate into gametes (eggs, sperm)
-Meiosis 1
-Meiosis 2 (see other lecture for details)
Meiosis 1 contributes to genetic variation:
• Crossing over produces recombinant chromosomes
• Humans – 23 chromosomes = 223 = 8.4 million combinations
• Egg + sperm = zygote = 223 x 223 = 70 trillion combinations

31
Q

What is non-disjunction?

A

• Abnormal sister chromatid separation, causes:
• Aneuploidy – different chromosome number from normal
• Complete or partial omission of X chromosome
-Trisomy

BIO111 Cell Biology (11 decks)

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