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Biology > 1.4 DNA and protein synthesis > Flashcards

1.4 DNA and protein synthesis Flashcards

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1
Q

describe the structure of an nucleotide

A
  • Phosphate group ,5 carbon sugar and a nitrogenous base
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2
Q

Name the pentose structure in DNA and RNA

A

DNA = Deoxyribose
RNA = ribose

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3
Q

Describe how a poly nucleotide is formed

A
  • Condensation reaction happens between nucleotides to form strong phosphodiester bonds.
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4
Q

What is the difference between a pruine base and nitrogenous base

A

Purine bases - Have two nitrogen containing rings. In DNA these are Adenine and Guanine
Nitrogenous base - Have one nitrogen containing rings. In DNA these are cytosine and thymine and in RNA this is cytosine and uracil

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5
Q

40% of a nucleotide in a sample of DNA contained the base guanine. Calculate the proportion of the other nucleotides

A

40 % guanine : 40% cytosine
10 % adenine : 10% thymine

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6
Q

What are some differences in RNA and DNA

A
  • DNA found in nucleus and RNA found in cytoplasm
  • DNA molecules are very long molecules where as RNA are relatively short compared to DNA .
    -DNA has a double helix structure of two polynucleotide chains , where as RNA is just polynucleotide strand
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7
Q

Why is DNA replication important?

A

Because when a cell divides into two, both daughter cells must contain a full set of DNA

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8
Q

What phase does DNA replication take place ?

A

Interphase

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9
Q

Explain the role in DNA helicase in DNA replication

A
  • Catalyses the breaking of the hydrogen bonds between base pairs to un ravel double helix
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10
Q

Why is DNA replication described as Semi conservative ?

A

Stands from DNA molecules act as templates , new DNA molecule contains one old DNA strand and one new.

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11
Q

Describe the process of DNA replication

A
  • DNA helicase attaches to DNA molecule and catalyses the breaking of hydrogen bonds between bases to unwind strand.

-Free nucleotides line up against their complimentary bases on the DNA strand

-Then DNA polymerase moves down the DNA molecule and catalyses the formation of phosphodiester bonds between the free nucleotides and DNA strand. (Condensation)

-DNA ligase joins up the shorter strands of polynucleotides on the lagging strand of DNA.

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12
Q

Why is it important that the activated nucleotides lose two phosphate groups when bonded to the DNA

A

This provides energy for the reaction (ATP)

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13
Q

What are the two different isotopes of nitrogen

A

Nitrogen 14, light
Nitrogen 15, heavy

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14
Q

) Describe how the process of DNA replication produces two identical DNA molecules.
(4)

A

1 - Hydrogen bonds between nucleotides are broken by DNA helicase
2 -Complementary nucleotides bind to the exposed strands.
3 - Hydrogen bonds will only form between cytosine and guanine and thymine and adenine
4 - Leading strand is synthesised continuously but lagging strand requires DNA ligase to join up okazaki fragments

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15
Q

What is a gene ?

A

A sequence of bases on a DNA molecule coding for a sequence of amino acids on a polypeptide chain

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16
Q

What are every three bases called on DNA

A

A codon

17
Q

What do codons read for ?

A

A specific amino acid,

18
Q

What does the base sequence of a gene determine ?

A

The amino acid sequence in a polypeptide chain

19
Q

What is known as a degenerate code ?

A

When more than one triplet can code for the same amino acid.

20
Q

Describe the structure of tRNA and function of tRNA

A

Structure:
- Single stranded
- Folded to make a clover leaf shape, shape held in place via hydrogen bonds

Function:
- To attach to one of the 20 amino acids and transfer this amino acid to the ribosome to create polypeptide chain
- Specific amino acids attach to specific tRNA binding sites which is determined via the anti codon on tRNA

21
Q

What is meant by an anti-codon?

A

Three bases which are found on tRNA which are complimentary to mRNA

22
Q

Why are degenerate codes advantageous?

A

Some single base mutations may still code for the same amino acid.

23
Q

What are start and stop codons?

A

Some codes do not code for specific amino acids however they code for the start or stop of the amino acid.

24
Q

What is meant by non-overlapping

A

Each triplet is read separately in threes.

25
Q

Give three differences between RNA and DNA

A

DNA contains deoxyribose , RNA contains Ribose
DNA is double stranded forming a double helix, RNA is single stranded
DNA contains thymine whilst RNA contains uracil

26
Q

Give three differences between the process of DNA replication and Transcription

A
  • DNA replication uses DNA nucleotides, transcription uses RNA nucleotides
  • Replication uses DNA polymerase, transcription uses RNA polymerase
  • Transcription copies only the template DNA strand, replication copies both strands.
27
Q

Describe the process of Transcription

A

1 - DNA helicase binds to non coding region of DNA and breaks the hydrogen bonds between the two strands of DNA
2 - Template strand of DNA is exposed
3 - RNA then moves along the template strand and adds complementary nucleotides one at a time.
4 - RNA polymerase reaches the end of the anti sense strand and it detaches , mRNA then leaves via the nuclear pore and goes to ribosome.

28
Q

Describe the process of translation

A
  • Modified mRNA molecule attaches to ribosome in the cytoplasm
  • tRNA carries amino acid
  • tRNA molecule with the complimentary anti codon is attracted to complimentary codons in mRNA and hydrogen bonds form between them
  • tRNA brings correct amino acid and peptide bonds are created between the amino acids
  • Peptide bond created via condensation reaction
  • tRNA is released from ribosome when it reaches stop codon
29
Q

Where does this new polypeptide go to get modified

A

The golgi apparatus

30
Q

What are gene mutations

A
  • A change in the DNA base sequence at a single location
31
Q

Explain a substitution mutation

A
  • Amino acid in polypeptide is altered.
  • mRNA transcribed contains a different codon
  • Codons code for a different amino acid therefore produces a different polypeptide
  • Polypeptide folds in a different shape therefore functioning protein not made
32
Q

How does sickle cell anemia happen?

A

One single substituion of an amino acid which changes one amino acid in Haemoglobin

33
Q

What is a deletion mutation?

A
  • A base is deleted from DNA, frame shift occurs
  • All mRNA codons are different
  • When polypeptide chain is formed, all amino acids are changed and one is completely missing
    -Polypeptide is folded in the wrong way and a functioning protein is not made
34
Q

What are insertion mutations?

A

When a new nucleotide is added into the base sequence.

35
Q

Explain insertion mutations

A
  • Changes the amino acid which would have been coded for the original triplet of bases.
  • Has knock on effect for other base triplets which causes a frame shift
36
Q
A

Biology (16 decks)

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