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Biology HL IB 2020-22 > 2.7 DNA replication, transcription and translation > Flashcards

2.7 DNA replication, transcription and translation Flashcards

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1
Q

Is DNA replication conservative, semi conservative or dispersive and why?

A

Semi-conservative because each nitrogenous base can only pair with its complementary base

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2
Q

What is semi-conservative replication?

A

When one strand is from the original template and the other is newly synthesized

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3
Q

Who proposed the theory of semi-conservation?

A

Meselson and Stahl

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4
Q

What does the conservative theory propose?

A

Claims that an entirely new model is synthesized using a DNA template with the template remaining unaltered

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5
Q

What does the dispersive theory claim?

A

That new DNA molecules are randomly composed of old and new DNA

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6
Q

Meselson-Stahl: Which radioactive isotopes did they use?

A

Nitrogen-14 and Nitrogen-15

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7
Q

Meselson-Stahl: Why was nitrogen used?

A

It is a key component of DNA

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8
Q

Meselson-Stahl: Which is lighter, N-14 or N-15?

A

N-14 as it has one less neutron

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9
Q

Meselson-Stahl: How were the DNA molecules modified and prepared for the experiment?

A

E. coli was put into N-15 and then induced to replicate twice in presence of N-14

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10
Q

Meselson-Stahl: How were the DNA molecules separated into their components?

A

Through caesium chloride density gradient centrifugation

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11
Q

Meselson-Stahl: How did the division of DNA disprove conservative and dispersive theories?

A
  • After first replication, molecules showed both N-14 and N-15 disproving the conservative
  • After second replication, some molecules only showed only N-14, disproving dispersive theory
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12
Q

Meselson-Stahl: How could one analyze densities of the DNA?

A

Through bands that formed in the tubes of DNA

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13
Q

Meselson-Stahl: Will the densities ever change after constant replication?

A

Densities will mostly remain the same. There will be more strands consisting of only N-14 however a parent strand containing one N-15 and one N-14 will always remain

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14
Q

During which phase of the cell cycle does DNA replication occur?

A

During S phase

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15
Q

What is the function of DNA replication?

A

Necessary in process of growth and biological inheritance. Helps create more identical strands of DNA

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16
Q

What stays unchanged in replication?

A

Number of chromosomes and genes

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17
Q

Outline the steps of replication briefly

A
  1. DNA is tightly wound around histones so they have to be unwound to make it accessible to enzymes
  2. Helicase unwinds double helix and separates DNA strands by breaking hydrogen bonds
  3. Once exposed, DNA polymerase starts making new strand using two old strands as templates
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18
Q

What does helicase do?

A
  • Unwinds double helix and unzips the DNA

- Breaks hydrogen bonds between bases

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19
Q

What is the role of DNA polymerase?

A

Creates new complementary strands

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20
Q

How does DNA polymerase make a new strand?

A

It collects free deoxy-nucleoside triphosphate and aligns to the complementary base. It then cuts off the two excess phosphates and uses the energy released to join the new nucleotide with the new strand

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21
Q

What direction does polymerase move in?

A

5’ to 3’ direction. They move in opposite directions on both strands

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22
Q

What is PCR?

A

Polymerase chain reaction

23
Q

What is the function of PCR?

A

It is a technique used to make many copies of a certain DNA sequences

24
Q

What are the 3 main steps of PCR?

A
  1. DENATURATION: Heat the DNA to high temps (95C for 15 seconds) so H bonds between strands break
  2. ANNEALING: DNA is then cooled to 54C and primers start to bind to target sequence
  3. ELONGATION: Synthesis of double stranded DNA where Taq DNA increases rate of replication
25
Q

Why is Taq polymerase used in PCR? i.e. State a property of Taq polymerase

A
  • It is an enzyme used to increase the rate of replication in DNA and it can add around 1000 nucleotides per minute
  • It is also heat-stable so it can withstand 95C and work at 54C but it is optimum at 72C
26
Q

Where is Taq polymerase isolated from?

A

It is isolated from ‘Thermus aquaticus’.

27
Q

What are primers?

A

Primers are a large excess of short sections of single-stranded DNA

28
Q

Functions of primers in PCR

A

They bind rapidly to target sequences and prevent re-annealing of the parent strands. They are the starting point of DNA synthesis

29
Q

Molecular structure of helicase

A

Formed from multiple polypeptides and it is doughnut in shape

30
Q

How does helicase move in DNA?

A

Unidirectionally

31
Q

In DNA replication, what is the importance of complementary base pairing in conserving the base sequence?

A

The new strand has to be completely identical to the sense strand otherwise there could be mutations or dangerous side effects

32
Q

How can PCR be used in real life?

A

DNA profiling, recombination and identification (eg. parents, forensic)

33
Q

What all apparatus is required for PCR?

A

Thermal cycler, primers, free DNA nucleotides, and DNA (Taq) polymerase

34
Q

What is transcription?

A

When coding information is copied or transcribed into mRNA

35
Q

What does mRNA change when being transcribed?

A

Uracil is used instead of Thymine to complement Adenine

36
Q

What is the antisense and sense strand?

A
  • The antisense strand is the one transcribed and is complementary
  • The sense strand is not transcribed and has the same sequence as mRNA except for T and U
37
Q

Steps of transcription

A
  1. RNA polymerase binds to site on DNA
  2. RNA polymerase separates strands and synthesizes complementary RNA nucleotides
  3. Bonds ribonucleoside triphosphates to complementary base and cleaves 2 phosphates
  4. RNA polymerase detaches
  5. RNA detaches and forms mRNA
  6. Double helix reforms
  7. mRNA moves to cytoplasm
38
Q

How is RNA polymerase different from DNA polymerase?

A

DNA polymerase is used in replication while RNA polymerase is used in transcription

39
Q

What are codons?

A

The base sequences (3 bases each) of an mRNA molecule that encodes for production of polypeptides

40
Q

How are mRNA sequences read by ribosomes?

A

In triplets of bases (codons)

41
Q

How many amino acids does each codon code for?

A

1

42
Q

Genetic code

A

A set of rules by which information coded within mRNA sequence determines order of amino acids

43
Q

How many possibilities of codons are there?

A

4 bases and 3 bases per codon= 4^3= 64 possibilities

44
Q

There are only 20 amino acids so what does that say about the 64 different possible codons?

A

Some are degenerate and so they will code for the same protein and hence share the same function

45
Q

How to use codon wheels/tables

A

Deduce the codons in mRNA and find the protein it encodes respectively

46
Q

Start codon

A

AUG

47
Q

What is translation?

A

Process of protein synthesis in which genetic information encoded in mRNA is translated into a sequence of amino acids in a polypeptide chain

48
Q

What do ribosomes consist of?

A

A large and small subunit

49
Q

How are ribosomal subunits assembled?

A

Like a sandwich. Each subunit is composed of RNA molecules.

  • The small subunit binds to the mRNA
  • The large subunit has binding sites for tRNA and also catalyzes peptide bonds between amino acids
50
Q

Process of translation

A
  1. Ribosomes bind to mRNA and move along in 5’-3’ direction
  2. Anticodons on tRNA align with complementary bases
  3. tRNA carries specific amino acid according to code
  4. Ribosomes catalyze formation of peptide bonds between adjacent amino acids (condensation)
  5. Ribosome moves along mRNA molecule synthesizing a chain until it reaches stop codon
  6. Translation stops and polypeptide chain is released
51
Q

What does it mean by “genetic code is universal” and how is it helpful?

A

Almost every organism has the same code and so genetic information is transferrable between species

52
Q

How is concept of ‘universality’ applied to production of insulin? Outline the process (Don’t go into detail about process of gene transfer)

A
  1. Gene responsible for insulin production is extracted from human cell
  2. It is spliced into a plasmid vector for autonomous replication and expression.
  3. Plasmid is then inserted into bacterial cell (usually E. coli)
  4. Transgenic bacteria is selected and cultured in a fermentation tank
  5. Bacteria produces human insulin in large numbers.
  6. Insulin is then harvested, purified and packaged for human use
53
Q

How many tRNA binding sites do the large subunit contain?

A

3 sites

54
Q

Outline key steps in process of gene transfer

A
  1. Restriction enzymes cut require gene from human genome
  2. Plasmids (Small circles of DNA) are removed from E. coli
  3. Same restriction enzyme is used to cut plasmid so same bases are left exposed, creating sticky ends
  4. Ligase joins sticky ends, fixing gene into plasmid
  5. Recombinant plasmid is inserted into host cell where it expresses new gene and replicates

Biology HL IB 2020-22 (24 decks)

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