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MED 109- BIOLOGY II > 15. CHROMOSOME STRUCTURE > Flashcards

15. CHROMOSOME STRUCTURE Flashcards

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1
Q
  1. What are Chromosomes?
A
  • they are DNA packed with proteins
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2
Q
  1. What are Bacterial chromosomes?
A
  • they are different from Eukaryotic chromosomes
  • they are double-stranded circular DNA molecules
  • they are associated with a small amount of protein
  • the DNA is supercoiled in the nucleoid
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3
Q
  1. What are Eukaryotic Chromosomes?
A
  • they are double stranded, linear DNA molecules
  • they are associated with a large amount of proteins
    (these are known as histones)
  • they are located in the nucleus
  • they consist of chromatin
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4
Q
  1. What is Chromatin made up of?
A
  • it is made up of DNA and histones
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5
Q
  1. What do the Chromosomes do in order to fit into the nucleus?
A
  • they become packed and supercoiled into different
    levels
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6
Q
  1. What is Level 1 of the Chromatin Packing in a Eukaryotic Chromosome?
A
  • the DNA Double Helix
  • it is 2nm in diameter
  • this is 20 Å
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7
Q
  1. What happens in between Level 1 and Level 2 of Chromatin Packing in a Eukaryotic Chromosome?
A
  • there are histones present
  • the histones join together with each other
  • they join together with the DNA
  • the form Nucleosomes
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8
Q
  1. What is Level 2 of the Chromatin Packing in a Eukaryotic Chromosome?
A
  • Nucleosomes
  • these are also known as Beads on a string
  • they are 10 nm in diameter fibre
  • this is 100 Å

NB:
- these beads on a strong can also be 11nm in
diameter
- this is 110Å
- this is only is we count the first nucleosome (H1)
which sits outside the rest of the structure

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9
Q
  1. What is Level 3 of the Chromatin Packing in Eukaryotic Chromosomes?
A
  • There is now a 30nm in diameter Chromatin Fibre
  • this is formed by the Nucleosomes wrapping around
    each other
  • this is 300Å
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10
Q
  1. What is Level 4 of the Chromatin Packing in Eukaryotic Chromosomes?
A
  • there are now Looped domains
  • these are formed by Chromatin fibres that form loops
  • these are 300nm in diameter
  • this is 3000Å
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11
Q
  1. What is Level 5 of the Chromatin Packing in Eukaryotic Chromosomes?
A
  • this is the chromatid
  • it is 700nm in diameter
  • this is 7000Å
  • two chromatids join together
  • this forms the Metaphase (Replicated) Chromosome
  • this is 1400 nm
  • this is 14 000Å (1.4µ)
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12
Q
  1. Does this diagram make sense?
A
  • yes
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13
Q
  1. What is the Nucleosome structure?
A
  • this is DNA wrapped twice around a histone cone
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14
Q
  1. What does each Nucleosome consist of?
A
  • it consists of 8 Histone Molecules
  • it consists of double stranded DNA
    (168 base pairs of it)
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15
Q
  1. How do we write the equation for a Nucleosome?
A
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16
Q
  1. Where is the H1 located?
A
  • it is found between the nucleosomes
  • it is not a part of the structure of the Nucleosome
    structure
17
Q
  1. What is the role of the H1?
A
  • it stabilises the interaction between DNA and
    nucleosomal histones
18
Q
  1. What are the 2 types of Chromatin?
A
  1. Euchromatic
  2. Heterochromatin
19
Q
  1. What is Euchromatin?
A
  • this is loosely packed chromatin
  • this is the active form of chromatin
  • it enables gene expression
  • it enables replication
  • it enables transcription
  • it is found in the nucleus
20
Q
  1. What is Heterochromatin?
A
  • this is highly condensed chromatin
  • this is the inactive form of chromatin
  • it inhibits replication
  • it inhibits transcription
  • it inhibits gene expression
  • it is found in the nucleus
21
Q
  1. What does Chromatin undergo during the cell cycle?
A
  • it undergoes changes in packing
22
Q
  1. What happens to Chromatin during Interphase?
A
  • most of the chromatin is Euchromatin
  • it is loosely packed
  • it enables gene expression
  • the chromosomes are not condensed
  • some of the chromatin are organised into a 10-nm
    fibre
  • most of the chromatin is compacted into a 30-nm fibre
23
Q
  1. What happens to the Chromatin during Mitosis?
A
  • the chromatin is highly condensed into
    Heterochromatin
  • this inhibits gene expression
24
Q
  1. What are the exceptions to the changes that the chromatin experiences during the cell cycle?
A
  • Centromeres
  • Telomeres
  • these are always highly condensed into
    Heterochromatin
25
Q
  1. What stages does Interphase consist of?
A
  • G1
  • S1
  • G2
26
Q
  1. What are Centromeres?
A
  • they are structures that connect 2 chromatids together
27
Q
  1. What are Telomeres?
A
  • they are found at the end of chromosomes
  • they prevent the erosion of chromosomes from
    happening

MED 109- BIOLOGY II (90 decks)

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