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Topic 1) Biological Molecules - PMT Flashcards > 1.5 - Nucleic Acids, 1.6 - ATP > Flashcards

1.5 - Nucleic Acids, 1.6 - ATP Flashcards

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Organic Chemistry 101 flashcards
1
Q

What is a nucleotide?

A

A type of biological molecule, they’re the monomers that make up DNA & RNA.

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2
Q

What is a nucleotide composed of?

A

1 pentose sugar
1 nitrogen-containing organic base
1 phosphate group

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3
Q

What is a pentose sugar?

A

A sugar with 5 carbon atoms

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4
Q

What is meant by ‘organic’?

A

It contains carbon.

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5
Q

Name the pentose sugar in DNA.

A

Deoxyribose

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6
Q

Name the pentose sugar in RNA

A

Ribose

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7
Q

State the role of DNA in living cells.

A

Base sequence of genes for functional RNA & amino acid sequence of polypeptides.
Used to store genetic information determines inherited characteristics = influences structure & function of organisms.

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8
Q

State the role of RNA in living cells.

A

Transfer genetic information from the DNA to the ribosomes.

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9
Q

What does DNA stand for?

A

Deoxyribonucleic acid.

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10
Q

What does RNA stand for?

A

Ribonucleic acid

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11
Q

What is a polynucleotide?

A

A polymer of nucleotides.
Both DNA & RNA nucleotides form polynucleotides.

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12
Q

How do polynucleotides form?

A

Via condensation reactions between the phosphate group of one nucleotide & the pentose sugar of another.
This forms a phosphodiester bond (1phosphate group + 2 ester bonds)
Strong chain of sugars and phosphate = sugar-phosphate backbone.

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13
Q

Describe the structure of DNA.

A

Double helix of 2 polynucleotide strands
Hydrogen bonds between bases are complementary:
Adenine + thymine
Guanine + cytosine

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14
Q

How many hydrogen bonds from between adenine and thymine?

A

2

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15
Q

How many hydrogen bonds form between guanine & cytosine?

A

3

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16
Q

What is base ‘A’?

A

Adenine

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17
Q

What is base ‘T’?

A

Thymine

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18
Q

What is base ‘G’?

A

Guanine

19
Q

What is base ‘C’?

A

Cytosine

20
Q

Name the complementary base pairs in RNA.

A

Adenine + uracil (2 hydrogen bonds)
Guanine + cytosine ( 3 hydrogen bonds)

21
Q

Which base in DNA is replaced by which base in RNA?

A

Thymine is replaced by uracil.

22
Q

Relate the structure of DNA to its functions.

A
  • Sugar-phosphate backbone & many H-bonds provide stability.
  • Long molecule to 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 easily for replication.
23
Q

What does the m stand for in mRNA?

A

Messenger

24
Q

Describe the structure of 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.
25
Q

Relate the structure of mRNA to its functions.

A
  • Shorter polynucleotide breaks down quickly so no excess polypeptide forms.
  • Single-stranded and linear so ribosome can move along strand & tRNA can bind exposed bases.
  • Complementary codon sequence to exons of 1 gene of 1 DNA strand so can be translated into a specific polypeptide by ribosomes.
26
Q

Describe the structure of transfer RNA

A
  • Single strand of about 80 nucleotides
  • Folded into clover shape
  • Anticodon on one end, amino acid binding site on the other:
    Anticodon binds to complementary mRNA codon,
    Amino acid corresponds to anticodon.
27
Q

What does the t stand for in tRNA?

A

Transfer

28
Q

Order DNA, mRNA & tRNA according to increasing length.

A

tRNA
mRNA
DNA

29
Q

Why did scientists initially doubt that DNA carried the genetic code?

A

As it’s a chemically simple molecule with few components.

30
Q

Why is DNA replication described as ‘semi-conservative’?

A

Strands from original DNA molecule act as a template.
New DNA molecule contains 1 old strand + 1 new strand.

31
Q

Outline the process of semi-conservative DNA replication.

A

Enzyme DNA helicase breaks hydrogen bonds between base pairs.
Helix unwinds to form 2 single strands.
Each original strand acts as a template; free-floating nucleotides are attracted to their complementary exposed bases of original strand.
Enzyme DNA polymerase catalyses condensation reactions that join adjacent nucleotides on new strand (phosphodiester bonds)
Hydrogen bonds from between bases on new & old strand.

32
Q

Describe the Meselson-Stahl experiment.

A

2 samples of bacteria were grown - 1 in medium containing light nitrogen isotope 14N & 1 in heavy 15N.
Sample from each was spun in centrifuge. Bacteria from 15N settles lower down tube that 14N as DNA nucleotides taken up during replication were heavier.
Bacteria from heavy were placed into broth containing light nitrogen.
After 1 round of DNA replication, sample was spun in centrifuge.
Sample settles in middle, showing that it contained a mixture of light & heavy nucleotides.
Bacterial DNA had replicated semi-conservatively in the light nitrogen.

33
Q

What does ATP stand for?

A

Adenosine triphosphate

34
Q

Describe the structure of ATP

A

Nucleotide base adenine
Combined with a ribose sugar
And 3 phosphate groups.
Known as a nucleotide derivative (modified form of a nucleotide)

35
Q

Why is ATP needed to release energy?

A

Plant & animal cells release energy from glucose (respiration).
But a cell can’t get energy directly from glucose.
In respiration, energy released by glucose is used to make ATP.

36
Q

How does ATP release energy?

A

ATP diffuses to part of cell that needs energy.
Energy in ATP is stored in bonds between phosphate groups.
It’s released via hydrolysis reactions.

37
Q

Describe how ATP is broken down?

A

Through a hydrolysis reaction
(Which requires a water molecule)
Catalysed by ATP hydrolase
Where a phosphate bond is broken
Products: ADP + Pi

38
Q

What is ADP?

A

Adenosine diphosphate

39
Q

What is a Pi?

A

Inorganic phosphate

40
Q

Describe how ATP hydrolysis can be ‘coupled’ to energy-requiring reactions?

A

The energy released by ATP hydrolysis can be used directly to make coupled reaction happen, rather than being lost as heat.

41
Q

What is ‘phosphorylation’?

A

This is where the inorganic phosphate released in ATP hydrolysis can be added to another compound, making the compound more reactive.

42
Q

How is ATP resynthesised in cells?

A

Enzyme ATP synthase catalysed condensation reaction between ADP & Pi
Happens during photosynthesis & respiration

43
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 means energy’s available quickly.
Readily re-synthesised.

Topic 1) Biological Molecules - PMT Flashcards (4 decks)

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