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BDS1 > Molecular biology 2 - nucleic acids > Flashcards

Molecular biology 2 - nucleic acids Flashcards

1
Q

Function of nucleic acids

A

protein synthesis and transmit genetic information

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2
Q

Which part of the nucleic acid is charged and has a direction (polarity)?

A

The phosphodiester backbone

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3
Q

Standard direction of nucleic acid strand

A

5’ to 3’

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4
Q

Structure of DNA

A

2 complementary strands joined by complementary base pairing which form a double helix around a central axis

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5
Q

Function of nucleases

A

enzymes that cleave/digest nucleic acid

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6
Q

Name of enzymes that digest DNA

A

deoxyribonucleases

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7
Q

Name of enzymes that hydrolyse RNA

A

ribonucleases

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8
Q

What are endonucleases?

A

enzymes that are able to cleave internal phosphodiester bonds

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9
Q

What are exonucleases?

A

Enzymes able to hydrolyse a nucleotide phosphodiester bond only when it is present at the terminal of the nucleic acid

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10
Q

Name of the classes of endonucleases that recognise specific sequences in DNA

A

restriction endonucleases (recognition site 4-6 bp long)

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11
Q

Outline of protein synthesis

A
  1. In the nucleus, DNA unzips by H bonds splitting to expose the base pairs on the template strand.
  2. Transcription - DNA polymerase copies base sequence in template strand to produce mRNA.
  3. Translation - mRNA is translated by tRNA, using ribosomes as a functional support.
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12
Q

What does DNA provide a template for?

A

DNA replication and transcription

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13
Q

Why do the number of base pairs / length of DNA increase for more complex organisms?

A

More complex organisms require more proteins.

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14
Q

Which bonds are broken during DNA denaturation?

A

Hydrogen bonds (no covalent bonds are broken)

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15
Q

How can the DNA double helix be denatured?

A

Using extremes of temperature and pH

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16
Q

What is the reversal of DNA denaturation?

A

Annealing (renaturation) - the 2 strands spontaneously rewind

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17
Q

How can annealing occur?

A

When the temperature/pH is returned to the normal range, the H bonds reform via complementary base pairing

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18
Q

Definition for the melting point of DNA

A

The temperature at which half the DNA is denatured (separated into single strands)

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19
Q

How does the composition of base pairs affect DNA melting point?

A

The higher its content of G=-C base pairs, the higher the melting point.

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20
Q

At the site of DNA where strand separation is initiated for DNA replication / transcription, which base pairs are most abundant?

A

A=T base pairs (only 2 H bonds so easier to break)

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21
Q

Order of abundance for 3 types of RNA

A

rRNA (80%), tRNA (15%), mRNA (5%)

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22
Q

Function of mRNA

A

Transfers information of the amino acid sequence of a polypeptide from DNA to ribosomes for translation.

23
Q

Which strand of DNA is mRNA complementary to?

A

Template strand

24
Q

Which strand of DNA is mRNA identical to (except T->U)?

A

Coding strand

25
Q

Name of base triplets in mRNA that code for an amino acid

A

codon

26
Q

Structure of tRNA

A

Hairpin structure with an amino acid arm and an anticodon arm (complementary to mRNA codon)

27
Q

Function of tRNA

A

Carries each amino acid to the ribosome (one specific tRNA for each amino acid)

28
Q

Sequence of translation

A
  1. mRNA binds to ribosome
  2. tRNA with a complementary anticodon to the mRNA codon aligns with mRNA by complementary base pairing
  3. Each type of tRNA carries a specific amino acid
  4. amino acids are covalently joined (peptide bond) by the ribosome to form a polypeptide.
29
Q

Structure of ribosomes

A

small and large subunits made of proteins and rRNA

30
Q

Genome definition

A

whole genetic information within a single cell nucleus

31
Q

How many possible tRNA molecules / base triplets exist?

A

64 (4^3)

32
Q

Key features of the genetic code

A

degenerate, unambiguous (one codon will code for only one amino acid), nonoverlapping, not punctuated (no skipping)

33
Q

What is meant by the genetic code being degenerate?

A

More than one codon can code for the same amino acid (as there are 64 codons but only 20 amino acids)

34
Q

Which base differs between degenerate codons?

A

3rd base position (wobble position)

35
Q

What is the wobble hypothesis?

A

A different base can be present in the 3rd base position but not the1st/2nd position

36
Q

What is the first amino acid in polypeptides?

A

Methionine (AUG is start codon)

37
Q

What signals the end of translation?

A

When a termination codon (UAA, UAG, UGA) is reached in mRNA.

38
Q

Name of tRNA molecule once an amino acid has bound

A

aminoacyl-tRNA

39
Q

Which ribosome subunit does the mRNA and tRNA bind to?

A

The small subunit. Then the large subunit will bind.

40
Q

What is a mutation?

A

Permanent alternation in a DNA (gene) sequence

41
Q

Causes of mutations

A
  1. spontaneous, low frequency errors in DNA synthesis
  2. chemical mutagens
  3. ionising radiation
42
Q

Name of mutation in which one base is switched for another

A

substitution

43
Q

Types of substitution mutations

A

conservative mutation, non-conservative mutation, no mutation

44
Q

what is a conservative mutation?

A

A type of substitution when one amino acid is replaced by one with similar properties

45
Q

What is a non-conservative mutation?

A

A type of substitution in which an amino acid is replaced by one with different properties

46
Q

How can a substitution be a silent mutation?

A

If the substitution occurs in the 3rd position of the codon this might not change the amino acid (degenerate, wobble hypothesis)

47
Q

How can a mutation change the length of the polypeptide?

A

A stop codon may be introduced or removed. A premature termination truncates the chain whereas a delayed termination elongates the polypeptide.

48
Q

Effect of insertion/deletion mutations

A

causes a frameshift which synthesises a protein with a different amino acid sequence downstream of the mutation. A stop codon may also be prematurely introduced or removed.

49
Q

Cause of sickle cell anaemia

A

single amino acid substitution (Glu -> Val) at position 6 in each beta chain of Hb due to a single base substitution.

50
Q

What type of substitution mutation causes sickle cell anaemia?

A

Non-conservative mutation because the amino acids have different properties (R group of valine is neutral whereas glutamate has a negative charge)

51
Q

How does the non-conservative substitution of Glu to Val in sickle cell anaemia alter Hb?

A

Hb has 2 fewer negative charges (substitution occurs in each beta chain) which produces a hydrophobic patch on Hb surface, causing the molecules to aggregate into bundles of fibres.

52
Q

Effects of sickle cell anaemia

A

Hb content of blood is about half the normal value because sickled cells are fragile and easily rupture (results in anaemia). Abnormal shape of sickled cells blocks capillaries causing pain and interfering with organ function.

53
Q

Symptoms of sickle cell anaemia

A

weak, dizzy, increased pulse, shortness of breath

BDS1 (50 decks)

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