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Alevel Biology OCR > 2.1.3 - Nucleotides and Nucleic Acids > Flashcards

2.1.3 - Nucleotides and Nucleic Acids Flashcards

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1
Q

What is a nucleic acid?

A

a polymer of nucleotides

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2
Q

What are nucleotides?

A

the monomers that makes up nucleic acids

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3
Q

What is a nucleotide made up of? (its basic structure)

A

a phosphate group
a pentose sugar
a nitrogenous base

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4
Q

Which pentose sugar is found in DNA?

A

deoxyribose

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5
Q

Which pentose sugar is found in RNA?

A

ribose

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6
Q

What nitrogenous bases are found in DNA?

A

adenine (A)
thymine (T)
guanine (G)
cytosine (C)

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7
Q

What nitrogenous bases are found in RNA?

A

adenine (A)
uracil (U)
guanine (G)
cytosine (C)

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8
Q

What are pyrimidines?

A

smaller bases which contain a single carbon ring structure
-cytosine, thymine(/uracil)

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9
Q

What are purines?

A

larger bases which contain double carbon ring structure
-adenine, guanine

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10
Q

What covalent bond is formed between nucleotides?

A

phosphodiester bond

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11
Q

What happens when two nucleotides join?

A

-condensation reaction
-phosphodiester bond formed
-phosphate group (C5) of one nucleotide joins with the hydroxyl group (C3) of the pentose of another nucleotide

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12
Q

What are the base pairing rules?

A

1) A always pairs with T/U
G always pairs with C
2) 2 hydrogen bonds form between A and T/U
3 hydrogen bonds form between C and G
3) Pyrimadines (C, T, U) always pair with purines (A, G)

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13
Q

What is the structure of DNA?

A

-2 strands of polynucleotides coiled into a double helix
-held together by hydrogen bonds between bases
-strands run in opposite directions, making them antiparallel (3->5 and 5->3)

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14
Q

What are the differences between DNA and RNA?

A

-pentose sugars -deoxyribose in DNA and ribose in RNA
-RNA has a uracil base where DNA has a thymine base
-DNA is double stranded but RNA is single stranded

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15
Q

What are the similarities between DNA and RNA?

A

-both have nucleotides as their monomer
-both have A, C and G bases
-both have phosphodiester bonds

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16
Q

Why is DNA replication semi-conservative?

A

the replicated DNA contains one newly formed strand and one original strand (which acts as a template)

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17
Q

What happens in DNA replication?

A

-DNA double helix unwinds (by DNA gyrase)
-the H-bonds between bases are broken (by DNA helicase)
-free activated DNA nucleotides complementary base pair to exposed bases
-DNA polymerase forms phosphodiester bonds between nucleotides

18
Q

What does the enzyme DNA gyrase do?

A

unwinds the DNA double helix

19
Q

What does the enzyme DNA helicase do?

A

breaks hydrogen bonds between bases

20
Q

What does the enzyme DNA polymerase do?

A

catalyses formation of phosphodiester bonds between nucleotides (forming sugar phosphate backbone)

21
Q

What is the leading strand in DNA replication?

A

the strand that is unzipped (by DNA polymerase) from the 3’ end -so is continuously replicated (undergoes continuous replication)

22
Q

What is the lagging strand in DNA replication?

A

the strand that is unzipped (by DNA polymerase) from the 5’ end (meaning DNA polymerase has to wait for a section to be unzipped and then work back along the strand) so undergoes discontinuous replcation
-in the lagging strand, the DNA is produced in sections (okazoki fragments) which DNA ligase joins together

23
Q

What does the enzyme DNA ligase do?

A

joins the Okazoki fragments in discontinuous replication together

24
Q

What is genetic code?

A

the sequence of bases in DNA, which acts as an instruction for the order of amino acids (ie the primary structure of a protein) when proteins are being produced

25
Q

What is a codon?

A

a three base sequence of DNA/RNA
-each codon codes for an amino acid

26
Q

What are the two stages of protein synthesis?

A

transcription (base sequences are copied and transported to ribosomes)
translation (complementary code is decoded by tRNA into primary structure of protein)

27
Q

What is the sense strand in protein synthesis?

A

DNA strand containing correct code to be synthesised

28
Q

What is the antisense strand in protein synthesis?

A

the complementary copy of the sense strand
(doesn’t code for protein but acts as template to produce DNA like the sense strand)

29
Q

What happens in transcription?

A

-DNA double helix is unwound and unzipped (H-bonds are broken)
-antisense strand acts as template strand
-free RNA nucleotides pair with complementary pairs on exposed antisense strand
-DNA polymerase forms phosphodiester bonds between RNA nucleotides
-mRNA leaves nucleus through pore in nuclear envelope (to travel to ribosome)
-double helix reforms

30
Q

What happens in translation?

A

-mRNA binds to ribosome at its start codon
-tRNA’s anticodon binds to a codon on mRNA (max 2 can at one time)
-peptide bond forms between amino acids on tRNA molecules (this is catalysed by peptidyl transferase)
-ribosome moves along mRNA and the tRNA from the first codon is released, leaving its amino acid attached to the next amino acid
-process continues (so a polypeptide chain forms) until the ribosome reaches the stop codon and the polypeptide chain is released

31
Q

What does ATP supply energy for?

A

-synthesis
-transport
-movement

32
Q

What is ATP made up of? (its structure)

A

-ribose sugar
-adenine (nitrogenous base)
-three phosphate groups

33
Q

Why is ATP a good energy source?

A

-small
-water soluble
-releases energy in small quantities
-easily regenerated

34
Q

Describe the procedure for extracting DNA

A

-grind sample
-mix with detergent
-add salt
-place in hot water bath
-add protease
-add layer of ethanol

35
Q

Why do you grind the sample in DNA extraction?

A

to break cell walls so that detergent can get inside cells

36
Q

Why do you mix with detergent in DNA extraction?

A

breaks cell membranes so that cell contents are released into the detergent

37
Q

Why do you add salt in DNA extraction?

A

breaks H-bonds between DNA bases and water

38
Q

Why do you place in hot water bath in DNA extraction?

A

stops enzymes from breaking DNA down

39
Q

Why do you add protease in DNA extraction?

A

breaks histamines in DNA down

40
Q

Why do you add a layer of ethanol in DNA extraction?

A

DNA doesn’t dissolve in alcohol so will precipitate

Alevel Biology OCR (26 decks)

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