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AS Level Biology Unit 1 > 1.4 Nucleic Acids > Flashcards

1.4 Nucleic Acids Flashcards

1
Q

What are the monomers of nucleic acids?

A

nucleotides

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2
Q

State the three components of
nucleotides

A

● Pentose sugar
● Organic base
● Phosphate group

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3
Q

What are the two types of organic base?

A

purine and prymidine

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4
Q

what is a purine?

A

● Class of organic bases
● Double ring structure
● Includes adenine (A) and guanine (G)

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5
Q

What is a pyrimidine?

A

● Class of organic bases
● Single ring structure
● Includes cytosine (C), thymine (T), uracil (U)

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6
Q

Describe the structure of a DNA
nucleotide

A

● Deoxyribose
● Organic base (A, T, C or G)
● Phosphate group

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7
Q

Describe the structure of an RNA
nucleotide.

A

● Ribose
● Organic base (A, U, C or G)
● Phosphate group

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8
Q

Describe the structure of an ATP
nucleotide

A

● Ribose
● Adenine
● Three phosphate groups

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9
Q

What is an endergonic reaction?

A

A non-spontaneous reaction that
requires an input of energy, e.g. ATP
formation

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10
Q

What is an exergonic reaction?

A

A spontaneous reaction that overall
releases energy, e.g. ATP hydrolysis.

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11
Q

Describe the role of ATP

A

Universal energy currency. Hydrolysed to
release energy:
ATP + Water ⇌ ADP + Pi + Energy

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12
Q

What is complementary base pairing?

A

● Describes how hydrogen bonds form between complementary purine and pyrimidine bases
● Two bonds form between A and T (or U)
● Three bonds form between G and C

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13
Q

Describe the structure of DNA

A

● Double-stranded polymer of nucleotides twisted to form a double helix
● Nucleotides joined by phosphodiester bonds
● Hydrogen bonds form between complementary base pairs,
A and T, C and G
● Antiparallel strands

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14
Q

Why are the strands of a DNA double
helix described as ‘antiparallel’?

A

The complementary strands run parallel but
in opposite directions, 5’ to 3’ and 3’ to 5’

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15
Q

Describe the structure of RNA

A

● Single-stranded polymer of nucleotides
● Nucleotides joined by phosphodiester bonds
● Hydrogen bonds form between complementary base
pairs, A and U, C and G

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16
Q

Name the three types of RNA
found in cells.

A

● Transfer RNA (tRNA)
● Messenger RNA (mRNA)
● Ribosomal RNA (rRNA)

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17
Q

What is the function of tRNA?

A

It carries specific amino acids to the
ribosomes.

18
Q

Describe the structure of tRNA.

A

● 80 nucleotides
● Single helix
● Clover leaf shape
● Anticodon on one end, amino acid binding
site on the other

19
Q

What is the function of mRNA?

A

Carries genetic information from the
nucleus to the ribosomes for protein
synthesis.

20
Q

Describe the structure of mRNA.

A

● 2000 nucleotides
● Single helix
● Unstable

21
Q

What is the function of rRNA?

A

Associates with proteins in the cytoplasm
to form ribosomes.

22
Q

Describe the structure of rRNA.

A

● 1800 to 5000 nucleotides
● Two subunits: one large, one small

23
Q

What is semi-conservative replication?

A

The replication of DNA to produce two new
DNA molecules which both contain one new
strand and one old strand from the original
DNA molecule.

24
Q

What is the role of DNA helicase in
semi-conservative replication?

A

It catalyses the unzipping of
double-stranded DNA into two single
strands, each of which acts as a template

25
What is the role of DNA polymerase in semi-conservative replication?
It catalyses the formation of phosphodiester bonds between nucleotides during the synthesis of a new DNA strand
26
What is the genetic code?
The rules by which triplets in a DNA base sequence code for the sequence of amino acids in a polypeptide chain. The genetic code is degenerate, universal and non-overlapping
27
Why is the genetic code described as degenerate?
More than one triplet can code for a particular amino acid.
28
Why is the genetic code described as universal?
The same codons code for the same amino acids in almost all organisms
29
What is meant by ‘non-overlapping’?
Each base in a sequence is read once and is only part of one triplet.
30
Describe the ‘triplet code’ for amino acids.
A specific sequence of three nucleotides (known as a codon) on a molecule of DNA or RNA codes for a particular amino acid in protein synthesis.
31
what is an exon?
A region of DNA that codes for an amino acid sequence
32
what is an intron?
A non-coding sequence of DNA that is found between exons
33
Compare eukaryotic and prokaryotic genes.
● Eukaryotic genes are discontinuous with non-coding introns and coding exons ● Prokaryotic genes are continuous with coding sequences only
34
what is protein synthesis?
The formation of proteins from amino acids. There are two stages: transcription and translation.
35
define transcription?
● First stage of protein synthesis ● The formation of pre-mRNA in eukaryotes and mRNA in prokaryotes from a section of the template strand of DNA
36
outline the process of transcription
1. DNA helicase unwinds section of DNA, breaking hydrogen bonds between the DNA strands. The antisense strand acts as a template. 2. RNA polymerase binds to the promoter region on a gene 3. Free RNA nucleotides align next to their complementary bases 4. RNA polymerase joins adjacent RNA nucleotides, forming phosphodiester bonds 5. RNA polymerase reaches stop codon and detaches. mRNA complete.
37
Describe post-transcriptional modification.
Splicing removes introns from pre-mRNA in eukaryotic cells.
38
define translation
● Second stage of protein synthesis ● Takes place in the ribosomes ● mRNA used as a template for the attachment of tRNA molecules with complementary anticodons. Amino acids carried on adjacent tRNA molecules are joined to form a polypeptide chain
39
outline the process of translation
1. mRNA attaches to groove between subunits of ribosome 2. Ribosome moves along mRNA until ‘start’ codon reached 3. Amino acid-tRNA complex anticodon attaches to complementary mRNA codon via hydrogen bonding. Another complex binds 4. Peptide bond forms between adjacent amino acids in the complexes 5. Ribosome moves along one codon and release empty tRNA. Process continues to form polypeptide chain until ‘stop’ codon is reached
40
The theory that each gene encodes a single protein.
The theory that each gene encodes a single protein.
41
What happens to the polypeptide after translation?
● Further modified by adding carbohydrates, lipids or phosphates ● Different polypeptides may be combined
42
Describe how DNA can be purified by precipitation.
● Add ethanol and a salt to aqueous solution. Nucleic acids precipitate out of solution ● Centrifuge to obtain pellet of nucleic acid ● Wash pellet with ethanol and centrifuge again

AS Level Biology Unit 1 (10 decks)

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