Nucleic acids + ATP Flashcards

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1
Q

Name the pentose sugars in DNA & RNA.

A

DNA: deoxyribose
RNA: ribose

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2
Q

State the role of DNA in living cells.

A

Base sequence of genes codes for functional RNA + amino acid sequence of polypeptides.
Carries genetic information + determines inherited characteristics = influences structure + function of organisms.

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3
Q

State the role of RNA in living cells.

A

mRNA: Complementary sequence to 1 gene from DNA with introns spliced out. Codons can be translated into a polypeptide by ribosomes.
rRNA: component of ribosomes (along with proteins)
tRNA: supplies complementary amino acid to mRNA codons during translation

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4
Q

How do polynucleotides form?

A

Condensation reactions between nucleotides form strong phosphodiester
bonds (sugar-phosphate backbone).

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5
Q

Describe the structure of DNA.

A

double helix of 2 deoxyribose strands
H-bonds between complementary purine &
pyrimidine base pairs on opposite strands:
adenine (A) + thymine (T)
guanine (G) + cytosine (C)

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6
Q

Which bases are purine and which are pyrimidine?

A

A & G = 2-ring purine bases

T & C & U = 1-ring pyrimidine bases

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7
Q

Name the complementary base pairs in DNA.

A

2 H-bonds between
adenine (A) + thymine (T)
3 H-bonds between
guanine (G) + cytosine (C)

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8
Q

Name the complementary base pairs in RNA.

A

2 H-bonds between
adenine (A) + uracil (U)
3 H-bonds between
guanine (G) + cytosine (C)

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9
Q

Relate the structure of DNA to its functions.

A

● sugar-phosphate backbone & many H-bonds provide stability
● long molecule stores lots of information
● helix is compact for storage in nucleus
● base sequence of triplets codes for amino acids
● double-stranded for semi-conservative replication
● complementary base pairing for accurate replication
● weak H-bonds break so strands separate for replication

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10
Q

Describe the structure of messenger RNA (mRNA).

A

● Long ribose polynucleotide (but shorter than DNA).
● Contains uracil instead of thymine.
● Single-stranded & linear (no complementary base pairing).
● Codon sequence is complementary to exons of 1 gene from 1 DNA strand.

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11
Q

Relate the structure of messenger RNA (mRNA) to

its functions

A

● Breaks down quickly so no excess polypeptide forms.
● Ribosome can move along strand & tRNA can bind to exposed bases.
● Can be translated into a specific polypeptide by ribosomes.

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12
Q

Describe the structure of transfer RNA (tRNA).

A

● Single strand of about 80 nucleotides.
● Folded into clover shape (some paired bases).
● Anticodon on one end, amino acid binding site on the other:
a) anticodon binds to complementary mRNA codon
b) amino acid corresponds to anticodon

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13
Q

Order DNA, mRNA and tRNA according to increasing length.

A

tRNA
mRNA
DNA

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14
Q

Why did scientists initially doubt that DNA carried the

genetic code?

A

Chemically simple molecule with few components.

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15
Q

Why is DNA replication described as

‘semiconservative’?

A

● Strands from original DNA molecule act as a template.

● New DNA molecule contains 1 old strand & 1 new strand.

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16
Q

Outline the process of semiconservative

DNA replication.

A
  1. DNA helicase breaks H-bonds between base pairs.
  2. Each strand 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.
17
Q

Describe 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 & 2 cycles of DNA replication.
  4. Centrifugation formed a pellet. Heavier DNA (bases made from 15N) settled closer to bottom of tube.
18
Q

Describe the structure of adenosine triphosphate

A

nucleotide derivative of adenine with 3 phosphate groups

19
Q

Explain the role of ATP in cells.

A

ATP hydrolase catalyses ATP → ADP + Pi
● Energy released is coupled to metabolic reactions.
● Phosphate group phosphorylates compounds to make them more reactive.

20
Q

How is ATP resynthesised in cells?

A

● ATP synthase catalyses condensation reaction between ADP & Pi
● during photosynthesis & respiration

21
Q

Explain why ATP is suitable as the ‘energy currency’ of cells.

A

● High energy bonds between phosphate groups.
● Small amounts of energy released at a time =less energy wasted as heat.
● Single-step hydrolysis = energy available quickly.
● Readily resynthesised.