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Biology > AS 1.6 Cell cycle and division > Flashcards

AS 1.6 Cell cycle and division Flashcards

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1
Q

What are chromosomes made out of?

A

DNA wrapped around histone proteins

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2
Q

When do chromosomes only become visible?

A

When chromatin condenses before cell division

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3
Q

After DNA replication, what do chromosomes exist as?

A

Chromosomes exist as two identical sister chromatids joined together by the centromere

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4
Q

What do chromosomes contain that code for specific polypeptides?

A

genes

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5
Q

How many chromosomes and pair of chromosomes do humans have?

A

46 chromosomes, 23 pairs

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6
Q

What is polyploidy?

A

When an organism has more than two complete sets of chromosomes

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7
Q

What does mitosis produce?

A

Two daughter cells that are genetically identical to the parent cell and each other

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8
Q

What phase is the majority of the cell cycle? and what occurs in that phase?

A

Interphase, where DNA, protein, and organelles are replicated

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9
Q

What are the 4 stages of mitosis

A

Prophase, metaphase, anaphase and telophase

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10
Q

What is cytokinesis

A

The division of the cytoplasm to form two daughter cells

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11
Q

What is interphase?

A
  • Longest phase in the cell cycle
  • Protein synthesis and organelle replication occurs so it requires a lot of ATP, therefore this phase is very metabolically active
  • Quantity of DNA doubles
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12
Q

Why is interphase metabolically active?

A

Protein synthesis and organelle replication occurs and it requires a lot of ATP

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13
Q

What happens in prophase?

A
  • Chromosomes condense to become shorter and thicker
  • Chromosomes become visible as two sister chromatids attached by a centromere
  • Centrioles move to opposite poles (not in higher plants)
  • Nuclear envelope disintegrates
  • Nucleolus disappears
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14
Q

What happens in metaphase?

A
  • Spindle forms

- Chromosomes align at the equator of the cell attached to spindle microtubules via the centromere

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15
Q

What happens in anaphase?

A
  • Spindle fibers shorten

- Centromeres divide, and chromatids are pulled towards opposite pole

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16
Q

What happens in telophase?

A
  • Chromatids reach poles and become indistinct by uncoiling
  • Nuclear envelope reforms
  • Nucleolus reforms
  • Spindle disintegrates
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17
Q

What happens in cytokinesis in animal cells?

A

the membrane infolds via a cleavage furrow, until the two cells become separated

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18
Q

What happens in cytokinesis in plant cells?

A

A cell plate develops from the center outwards, until the cell is divided by two

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19
Q

What can’t cytokinesis happen in plant cells the same way it happens in animal cells?

A

The presence of the cell wall prevents the membranes to infold

20
Q

What is the significance of mitosis?

A
  • By producing new cells, organisms can grow, repair tissues and replace dead cells
  • In animals, skin and blood cells are constantly being replaced as they wear out
  • In plants, cells at the shoot and root top meristems are constantly undergoing mitosis
  • Mitosis is important in asexual reproduction where genetically identical offspring can be produced resulting in a rapid increase in numbers during favorable conditions
21
Q

What results in uncontrollable cell division?

A
  • Mitosis is controlled by a number of genes including proto-oncogenes. A mutation in one of these genes from chemicals or radiation from UV light causes them to turn into oncogenes. This results in uncontrollable cell division, which leads to the formation of tumors and cancers.
22
Q

What is the mitotic index?

A

the ratio of the number of cells in a population undergoing mitosis to the number of cells not undergoing mitosis, it is a measure of growth

23
Q

How do you calculate the length of a stage in the cell cycle?

A
  1. Calculate the proportion of cells that is in that stage

2. Multiply the proportion to the length of the cell cycle

24
Q

What is meiosis?

A

two consecutive cell divisions, it produces four genetically different haploid cells

25
Q

Where does meiosis occur?

A

It occurs in the reproductive orangs of animals, plants and some protoctistans before sexual reproduction

26
Q

When does interphase occur in meiosis? and what is it responsible for?

A

Interphase only occurs before prophase 1, and it is responsible for DNA replication and protein synthesis

27
Q

Why is it important that the chromosome number halves during gamete formation?

A

If the chromosome number did not halve during gamete formation, the number of chromosomes would double every generation

28
Q

Why is prophase 1 in meiosis different from prophase in mitosis? and what does it do?

A

when homologous pairs come together to form bivalents, crossing over may occur and this increases genetic variation

29
Q

Why is metaphase 1 in meiosis different from metaphase in mitosis?

A

bivalents align randomly at the equator, this is independent assortment (2^23 more variants from 23 bivalents)

30
Q

What happens in prophase 1?

A
  • Chromosomes condense to become shorter and thicker
  • Centrioles move to opposite poles (not in higher plants)
  • Chromosomes come together in homologous pairs (bivalent)
  • Crossing over occurs, part of one chromatid is exchanged with another
  • Nucleolus and nuclear membrane disappear
31
Q

What happens in metaphase 1?

A
  • Spindle forms
  • Homologous chromosome pairs (bivalents) align at the equator of the cell attached to spindle microtubules via cintroeme
  • The alignment of bivalents are random and is called independent assortment
32
Q

What happens in anaphase 1?

A
  • Spindle fibers shorten

- Bivalents separate and chromosomes are pulled towards opposite poles

33
Q

Why is anaphase 1 in meiosis different from anaphase in mitosis?

A

Chromosomes are pulled to opposite poles in meiosis 1, not chromatids

34
Q

What happens in telophase 1?

A
  • The chromosomes reach opposite poles

- In some cases, nuclear envelope reforms, nucleolus reforms, spindle disintegrates)

35
Q

What happens in cytokinesis in meiosis 1?

A

Division of cytoplasm occurs, creating two haploid cells

36
Q

What happens in prophase 2?

A

Centrioles separate, and arrange themselves at 90° to the old spindle

37
Q

What happens in metaphase 2?

A
  • Chromosomes align at the equator of the cell attached to spindle microtubules via centromere
  • Independent assortment occurs as the chromatids of the chromosomes can face either pole when they are aligned
38
Q

What happens in anaphase 2?

A
  • Spindle fibers shorten

- Centromeres divide, and chromatids are pulled towards opposite poles

39
Q

What happens in telophase 2?

A
  • Chromatids reach poles and become indistinct
  • Nuclear envelope reforms
  • Nucleolus reforms
  • Spindle disintegrates
40
Q

What is produced after cytokinesis in meiosis 2?

A

Four haploid daughter cells are produced

41
Q

What is the significance of meiosis?

A
  • It keeps the chromosome number constant from one generation to the next
  • Generates genetic variation through crossing over (prophase 1) and independent assortment (metaphase 1 and 2)
  • Genetic variation is essential for the survival of species in a constantly changing environment
42
Q

Which stage does crossing over occur?

A

Prophase 1 in meiosis

43
Q

Which stage does independent assortment occur?

A

In metaphase 1 and 2 in meiosis

44
Q

Why is genetic variation important?

A

Genetic variation is essential for the survival of species in a constantly changing environment

45
Q

What are the differences between meiosis 1 and 2?

A
  • Prophase in meiosis 1 follows DNA replication in interphase where prophase in meiosis 2 does not
  • Prophase 1 has crossing over where prophase 2 does not
  • In metaphase 1, homologous pairs align on the equator whereas in metaphase 2, chromatids align on the equator
  • In metaphase 1, independent assortment occurs with homologous chromosomes, where in metaphase 2, independent assortment occurs with chromatids
  • In anaphase 1, chromosomes are pulled to opposite poles, whereas in anaphase 2, chromatids are pulled to opposite poles
  • In anaphase 1, it produces 2 haploid daughter cells whereas in anaphase 2, 4 haploid daughter cells are produced
46
Q

What are the differences between mitosis and meiosis?

A 
Number of divisions:
Mitosis: one
Meiosis: two
Number of daughter cells produced:
Mitosis: two
Meiosis: four
Number of chromosomes in daughter cells:
Mitosis: same as parent cell
Meiosis: half of parent cell
Ploidy of daughter cells: 
Mitosis: diploid
Meiosis: haploid
Chiasmata (the site seen in a light microscope where the exchange of DNA in crossing over occurs):
Mitosis: present 
Meiosis: absent
Crossing over:
Mitosis: none
Meiosis: prophase 1
Independent assortment: 
Mitosis: none
Meiosis: metaphase 1 and 2
Genetic composition:
Mitosis: genetically identical with parent cell and each other
Meiosis: genetically different

Biology (9 decks)

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