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Structure + Function 1 > nucleic acids and chromatin > Flashcards

nucleic acids and chromatin Flashcards

1
Q

When are chromosomes visible in the cell cycle?

A

Metaphase

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2
Q

What is the ordered display of chromosomes called?

A

Karyotype

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3
Q

How do you count chromosomes and chromatids?

A

Chromosomes: number of centromeres

Chromatids: number of arms

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4
Q

What are telomeres?

A

Ends of a chromosome

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5
Q

what is the constricted region of a chromosome?

A

centromere

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6
Q

what is the role of the centromere?

A

act as the site of assembly of the kinetochore

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7
Q

What is the kinetochore?

A

Highly compex multiprotein structure that is responsible for the actual events of chromosome segregation

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8
Q

What is mitosis?

A

Cell division

Mother cell divides to produce 2 new daughter cells that are genetically identical itself

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9
Q

what is the 3 components of a nucleotide?

A
  • nitrogen-containing base
  • 5 carbon sugar
  • phosphate group
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10
Q

Nitrogen containing bases in DNA / RNA

A

Cytosine

Guanine

Thymine / Uracil

Adenine

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11
Q

Bonding between nitrogen containing bases?

A

Hydrogen bonds

C ≡ G

A = T/U

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12
Q

Molecular shape of double stranded DNA?

A

alpha helix

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13
Q

Describe the structure of a DNA molecule

A

2 linear strands

Held together by hydrogen bonds between base pairs

Run antiparallel to each other

5’ to 3’ and 3’ to 5’

Twist together

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14
Q

How are adjacent nucleotides of RNA and DNA linked?

What is formed?

A

Phosphodiester bonds

Sugar-phosphate backbone

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15
Q

Describe the positioning of the phosphodiester bond between 2 nucleotides

A

Phosphate group attached to 5’ C forms bond with OH group on 3’ of the adjacent nucelotide

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16
Q

In which direction does the sugar-phosphate backbone grow?

A

5’ to 3’ direction

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17
Q

How does the OH group on the ribose in RNA nucleotides affect it? (not present in DNA nucleotides)

A

Responsible for secondary structure

More susceptible to alkaline degredation

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18
Q

What is a histone?

A

Protein that associates with DNA in the nucleus

helps condense DNA into a smaller volume

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19
Q

What is chromatin?

A

Complex of DNA and proteins

Forms chromosomes within the nucleus of eukaryotic cells

20
Q

Describe 2 forms of chromatin

A
  • Euchromatin
    *less condensed
    *can be transcribed
  • Heterochromatin
    *more condensed
    *not usually transcribed
21
Q

Describe 2 forms of chromatin

A
  • Euchromatin
    *less condensed
    *can be transcribed
  • Heterochromatin
    *more condensed
    *not usually transcribed
22
Q

Most of the chromosome body is which type of chromatin?

A

euchromatin

23
Q

What are nucleosomes?

Approximate diameter?

A

Fundamental subunit of chromatin

Where chromatin has wrapped around a histone

bead on a string

11nm

24
Q

what is a histone octamer

A

8 proteins called histones

25
Q

What charge do histone core proteins have?

A

Positive - binds tightly to the negatively charged DNA backbone

26
Q

Each nucleosome has how many turns of DNA?

What are they wrapped around?

A

1.65 turns

8 histones - histone octamer

27
Q

What makes up the histone octamer?

A

2 copies of each histone proteins:

H2A

H2B

H3

H4

28
Q

Which histone is not part of the histone octamer?

Where is it found?

A

H1

found in Nucleosome linker DNA

linker DNA is between nucleosomes

29
Q

Nucleosomes fold around each other to form…

A

Chromatin fibre

30
Q

What does chromatin fibre formation require?

What does it do?

A

H1

Binds linker DNA between nucleosome cores

Forms a chromatosome

31
Q

What does chromatin fibre formation require?

What does it do?

A

H1

Binds linker DNA between nucleosome cores

Forms a chromatosome

32
Q

what is chromatin remodelling?

A

when DNA “opens” using remodellers for gene expression to take place

Cell’s chromatin ‘opens’ using remodellers

Allows access to the DNA for transcription

33
Q

Describe ATP-dependent chromatin remodelling

A

ATP-dependent chromatin remodelling complex

Moves, ejects, or restructures nucleosome

Exposes DNA to transcription proteins

34
Q

Two ways of chromatin remodelling

A

Using ATP-dependent chromatin remodelling complexes

Enzymes modify the histone proteins in the nucleosomes

by adding / removing covalently bonded moieties

35
Q

Describe covalent histone modifications

A

Add/remove covalently bonded moieties to histone

Done by enzymes

HATs (histone acetyltransferases) - adds acetyl group

kinases - transfer phosphate groups

deacetylases - remove acetyl group

methyltransferases add methyl group

36
Q

How does remodelling chromatin mediate the activation of genes?

A

Exposes gene promoter sequences

Increases frequency of transcription

37
Q

What are histones rich in?

In which part?

A

Positively charged lysine residues

N terminus tails

extend out of nucleosome between DNA turns

38
Q

How can histone tails be modified?

Where does each modification occur?

A

Methylation of lysine and arginine
*inactivates

Acetylation of lysine
*activates

Phosphorylation of serine
*activate / deactivate

39
Q

What can modified histone tails act as?

A

Signals / Binding sites for regulatory proteins

some proteins promote condensation

some promote decondensation

easier to access dna

40
Q

What can modified histone tails act as?

A

Signals / Binding sites for regulatory proteins

some proteins promote condensation

some promote decondensation

easier to access dna

41
Q

Does methylation activate or deactivate chromatin?

A

deactivate

42
Q

Where in the chromosome is methylation common?

A

Heterochromatin areas ( places unlikely to contain any genes )

telomeres

centromere

43
Q

Where in the chromosome is methylation common?

A

Heterochromatin areas ( places unlikely to contain any genes )

telomeres

centromere

44
Q

Chromatin remodelling, DNA modification and histone modification influences the ____ but does not alter the ____

A

Influences phenotype

Not alter genotype

45
Q

Chromatin remodelling, DNA modification and histone modification influences the ____ but does not alter the ____

A

Influences phenotype

Not alter genotype

46
Q

Can modifications to DNA and histones be replicated?

A

yes

Structure + Function 1 (18 decks)

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