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Biology Year 12 > Nucleic acids (2) > Flashcards

Nucleic acids (2) Flashcards

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1
Q

Draw the structure of a nucleotide.

A

look at diagram in notes

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2
Q

What is the role of DNA in living cells?

A
  • base sequence of gene codes for functional RNA + amino acid sequence of polypeptides
  • genetic information determines inherited characteristics which influences structure + function of organisms
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3
Q

What are the 3 types of RNA?

A

mRNA
rRNA
tRNA

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4
Q

What is the role of mRNA in living cells?

A

complementary sequence to 1 gene from DNA with introns spliced out so codons can be translated into a polypeptide by ribosomes

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5
Q

What is meant by an intron?

A

non-coding region

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6
Q

What is the role of rRNA in living cells?

A

component of ribosomes

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7
Q

What is the role of tRNA in living cells?

A

supplies complementary amino acids to mRNA codons during translation

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8
Q

How do polynucleotides form?

A

condensation reactions between nucleotides form strong phosphodiester bonds

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9
Q

What is the structure of DNA?

A
  • double helix of 2 polynucleotide strands (deoxyribose)
  • H-bonds between complementary purine and pyrimidine base pairs on opposite strands
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10
Q

What are the 4 bases in DNA?

A

adenine + thymine
guanine + cytosine

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11
Q

How many bonds are between each of the base pairs in DNA?

A

A + T have 2 H-bonds between
G + C have 3 H-bonds between

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12
Q

What type of base are A and G?

A

2-ring purine bases

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13
Q

What type of base are T, C and U?

A

1-ring pyrimidine bases

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14
Q

Which bases are 2-ring purine?

A

A and G

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15
Q

Which bases are 1-ring pyrimidine?

A

T, C and U

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16
Q

What are the 4 bases in RNA?

A

adenine + uracil
guanine + cytosine

17
Q

Rank DNA, mRNA and tRNA from shortest to longest.

A

tRNA - mRNA - DNA

18
Q

What are 5 structures of DNA?

A
  • sugar-phosphate backbone
  • base sequence of triplets
  • double-stranded
  • complementary base pairing
  • many H-bonds
19
Q

What are 3 structures of mRNA?

3

A
  • contains uracil not thymine
  • single-stranded and linear
  • codon sequence is complementary to exons of 1 gene from 1 DNA strand
20
Q

What is the structure of tRNA?

A
  • single strand of about 80 nucleotides
  • folded into clover shape
  • anticodon on 1 end and amino acid binding site on the other
21
Q

What does the anticodon on tRNA do?

A

binds to complementary mRNA codon

22
Q

What did some scientists initially doubt and why?

A

Initially doubted DNA carried the genetic code as it’s a chemically simple molecule with few components

23
Q

What are 2 reasons why DNA replication is called semi-conservative?

A
  • strands from original DNA molecule act as a template
  • new DNA molecule contains 1 old strand and 1 new strand
24
Q

What are the 5 steps of semi-conservative DNA replication?

A

1) DNA helicase breaks H-bonds between base pairs
2) each strands acts as a template
3) free nucleotides from nuclear sap attach to exposed bases by complementary base pairing
4) DNA polymerase catalyses condensation reactions that join adjacent nucleotides on new strand
5) H-bonds reform

25
Q

What were the 4 steps of the Meselson-Stahl experiment?

A

1) bacteria were grown in a medium containing heavy isotope 15N for many generations
2) some bacteria were moved to a medium containing light isotope 14N
3) samples were extracted after 1 and 2 cycles of DNA replication
4) centrifugation formed a pellet - heavier DNA (bases made from 15N) settled closer to bottom of tube

26
Q

What was the name of the experiment using 14N and 15N?

A

Meselson-Stahl experiment

27
Q

How does having a sugar-phosphate backbone and many H-bonds relate to DNA’s function?

A

provides stability

28
Q

How does having a base sequence of triplets relate to DNA’s function?

A

code for amino acids

29
Q

How does being double-stranded relate to DNA’s function?

A

for semi-conservative replication

30
Q

How does having complementary base pairing relate to DNA’s function?

A

for accurate replication

31
Q

How does having H-bonds relate to DNA’s function?

A

they are weak so break so strands separate for replication

32
Q

How does containing uracil not thymine relate to mRNA’s function?

A

breaks down quickly so no excess polypeptide forms

33
Q

How does being single-stranded and linear relate to mRNA’s function?

A

so ribosome can move along strand and tRNA can bind to exposed bases

34
Q

How does having a codon sequence complementary to exons of 1 gene from 1 DNA strand relate to mRNA’s function?

A

so can be translated into specific polypeptide by ribosomes

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