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Biology > Structure of Chromosomes, Cell Cycle, and Cell Division > Flashcards

Structure of Chromosomes, Cell Cycle, and Cell Division Flashcards

1
Q

define chromosomes

A

highly coiled and condensed chromatin fibres

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2
Q

define chromatin

A

the complex of DNA and proteins making up chromosomes is known as chromatin

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3
Q

constituents of chromatin

A
  1. DNA (40%)
  2. Histones (60%)
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4
Q

structure of DNA

A

each DNA strand consists of three repeating nucleotides which are made of- phosphate, pentose (sugar) arranged lengthwise, and a nitrogenous base attached to the sugar, which extends to join the other complementary nitrogenous base.

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5
Q

types of nitrogenous bases

A
  1. Adenine
  2. Guanine
  3. Cytosine
  4. Thymine
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6
Q

types of bonds between bases

A
  1. Adenine forms double hydrogen bond with Thymine
    2 Guanine forms triple hydrogen bond with Cytosine
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7
Q

define histones

A

the proteins that help in the coiling and packaging of DNA into structural units called nucleosomes

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8
Q

define nucleosomes

A

the DNA strand winds around a core of 8 histone proteins (octamer), called nucleosome

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9
Q

structure of chromosomes

A
  1. contains two sister chromatids
  2. point of attachment of sister chromatids is called centromere
  3. centromere attaches spindle fibre during cell division
  4. spindle fibre contracts, sister chromatids re separated at centromere, and pulled away to the poles
  5. after cell division, chromatids decondense into chromatin fibres
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10
Q

define genes

A

specific sequence of nucleotides on a chromosome, that encode particular proteins which express in the form of some particular feature of the body

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11
Q

need for new cells

A
  1. growth
  2. replacement
  3. repair
  4. reproduction
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12
Q

where does mitosis occur

A

in cell divisions for growth, replacement and repair.
does not occur in reproduction (meiosis)

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13
Q

define cell cycle

A

the cell cycle is a series of events that take place in a cell leading to the duplication of its DNA and subsequent division of the cell to produce its two daughter cells

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14
Q

phases of cell cycle

A
  1. interphase: non-dividing phase
  2. mitosis/ M-phase: dividing phase
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15
Q

phases of interphase

A
  1. first growth phase (G1)
  2. synthesis phase (S)
  3. second growth phase (G2)
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16
Q

what happens in first growth phase

A
  1. RNA and proteins synthesized
  2. volume of cytoplasm increases
  3. Mitochondria/chloroplasts divide, and they have their own DNA
  4. cells can withdraw and enter resting phase (R), or enter synthesis phase
17
Q

what happens in synthesis phase

A

more DNA is synthesized, chromosomes are duplicated

18
Q

what happens in second growth phase

A
  1. RNA and proteins continue to be synthesized
19
Q

how is DNA formed

A
  1. during S phase, DNA duplicates for mitosis
  2. DNA double helix is opened and two strands are freed
  3. New strands begin to form
  4. process continues in a sequence for the whole length of the DNA
20
Q

types of cell divisions

A
  1. Mitosis to form diploid cells
  2. Meiosis to form haploid cells
21
Q

phases of mitosis

A
  1. karyokinesis (division of nucleus)
  2. cytokinesis (division of cytoplasm)
22
Q

phases of karyokinesis/ mitosis

A
  1. prophase
  2. metaphase
  3. anaphase
  4. telophase
23
Q

what happens in prophase

A
  1. chromosomes are short and thick and clearly visible
  2. chromosome duplicates into 2 chromatids
  3. centrosome splits in two while centrioles duplicate.
  4. daughter centrioles move apart to opp. poles
  5. each centriole is covered by radiating rays called ASTERS
  6. fibres formed between daughter centrioles called spindle fibres
  7. nuclear membrane and nucleolus disappear
  8. duplicated chromosomes start moving towards equator of cell
24
Q

what happens in metaphase

A
  1. duplicated chromosomes arrange on the equatorial plane
  2. each chromosome gets attached to spindle fibre at centromere
25
Q

what happens in anaphase

A
  1. centromere attaching the two chromatids divides
  2. sister chromatids separate and are drawn towards opposite poles (by contraction of spindle fibres)
26
Q

what happens in telophase

A
  1. each chromatid lengthens, forming chromatin threads
  2. nuclear membrane reappears
  3. nucleolus reappears in daughter nucleus
27
Q

what happens in cytokinesis

A
  1. furrow appears in cell membrane
  2. cytoplasm splits in two, forming two new cells `
28
Q

significance of mitosis

A
  1. growth
  2. repair
  3. replacement
  4. asexual reproduction
  5. maintains same chromosome number in daughter cell
29
Q

meiosis produces whatt

A

sex cells or the gametes

30
Q

division in meiosis

A

number of chromosomes in the sex cells is halved

31
Q

define synapsis

A

pairing of 2 homologous chromosomes that occur during meiosis

32
Q

significance of meiosis

A
  1. chromosome number is halved
  2. maternal and paternal chromosomes get mixed up during the reduction division
33
Q

define crossing over

A

when maternal and paternal chromosomes separate, chromatid material gets exchanged between the two members of homologous pair

34
Q

define chiasma

A

The X shaped structure formed due to crossing over between two non-sister chromatids of the paired homologous chromosomes

Biology (15 decks)

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