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Biology 1001A > Cycle 2 - Mitosis, Replication > Flashcards

Cycle 2 - Mitosis, Replication Flashcards

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1
Q

Describe interphase

A
  1. G1 phase
    • “G0 phase” (ex., neurons stop dividing once they are fully mature
    • Speed that cell divides at depends on length of G1
  2. S phase (DNA replication)
  3. G2 phase (centrosomes double)
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2
Q

Explain how DNA condenses during prophase

A

Chromosomes that were replicated during interphase begin to condense

  • DNA is compacted by winding the double helix twice around positive histones to form a nucleosome (10 nm chromatin fibre)
    • The linker extends between one nucleosome and the next
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3
Q

Describe prophase

A
  • As they continue to fold and condense, the chromatin fibres become visible
  • Mitotic spindle begins to form between “centrosomes”
  • Start migrating toward the opposite ends of the cell to form the spindle poles
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4
Q

Describe prometaphase

A
  • Starts when the nuclear envelope breaks down
  • Spindle microtubules grow from centrosomes and attach to the kinetochores
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5
Q

Describe metaphase

A

Spindle microtubules align chromosomes at spindle midpoint/metaphase plate/equatorial

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6
Q

Describe anaphase

A

Sister chromatids separate and move to opposite spindle poles

  • Microtubules push poles apart
  • Kinetochores walk down the spindle
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7
Q

Describe telophase

A
  • Spindle disassembles and the chromosomes decondense
  • Nucleolus reappears, RNA transcription resumes, new nuclear envelope forms
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8
Q

Describe cytokinesis

A

Animal, protists, fungi:

  • Furrowing –> microfilaments made of actin cleave
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9
Q

What is the meaning of “n” and “C”?

How does it change throughout mitosis?

A

n = number of unique chromosomes within the cell (chromosomes)

C = number of copies of the genome (chromatids)

Pre-S phase: 2n 2C

S-phase: 2n 4C

Telophase: 2n 2C

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10
Q

Explain DNA location and shape in eukaryotes and prokaryotes

A

Eukaryote DNA is found in the nucleus and it is linear. Several replication bubbles are required.

  • Note that organelle chromosomes (chloroplast, mitochondria) are circular

Prokaryotic DNA floats in the cytoplasm and is circular. One replication bubble is required and there are no DNA ends.

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11
Q

Describe the location of rapidly cycling cells in animals and plants

A
  • Animals:
    1. gametes (males)
    2. skin (abrasion)
    3. bone marrow (making blood, replenishing tissue)
      • Most cells are not actively cycling
  • Plants:
    1. at the very tips of roots
    2. leafs (growth)
    3. meristem tissue
      • Centre of the tree trunk is dead
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12
Q

State the composition of microtubules, intermediate filaments and microfilaments

A

Microtubules: tubulin protein

Intermediate filaments: several proteins

Microfilaments: made of actin

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13
Q

Outline the role of cell checkpoint

A

G1

  • A hormone or growth factor is absent
  • DNA is damaged

S and G2

  • DNA was not replicated fully in S
  • DNA is damaged

M phase

  • Checks chromosome misalignment
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14
Q

Describe the design, outcome and conclusions of the classic Meselson and Stahl experiment

A
  • Wondered how DNA replicated itself (semiconservative, conservative, dispersive)
  • Grew e. coli in heavy nitrogen N-15
  • When replicated, DNA used heavy nitrogen –> bred until all heavy nitrogen
  • Switched to living in N-14 –> new strand copied from template contains N-14
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15
Q

Draw a labelled replication bubble

A
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16
Q

Why do chromosomes shorten after each replication?

A

The removal of the end primers on the lagging strand of the last replication bubble cannot be filled in because there is no DNA to build off of (no 3’ OH to extend) and so overhang is created on the lagging side

17
Q

Explain the mechanisms in which telomerase elongates the telomeres

A
  • Telomerase brings its own template and binds to the 3’ overhang
  • Bases are added using telomerase RNA
  • Telomerase shifts forward to continue this process
  • Since only one small template is provided, this creates the repeated sequences
  • Primase is added, DNA polymerase extends to the left as needed, and finally ligase seals the nick
18
Q

How many telomers are there per one chromatid?

A

2 telomere for every 1 chromatid

19
Q

Explain the function of DNA polymerase I, II and III

A

Biology 1001A (12 decks)

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