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Biology > Section 4 - DNA, genes and protein synthesis > Flashcards

Section 4 - DNA, genes and protein synthesis Flashcards

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1
Q

What is a gene?

A

A section of DNA that contains coded information for making polypeptides and RNA.

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2
Q

What is a locus?

A

Fixed position of DNA molecule occupied by a gene.

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3
Q

What is an allele?

A

Different versions of the same gene, found at the same locus on a chromosome.

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4
Q

What is an exon?

A

Region of DNA that CODES for amino acid sequences.

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5
Q

What is an intron?

A

Regions of DNA that do not code for anything.

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6
Q

Why is genetic code known as degenerate?

A

Some amino acids can be coded for by more than one triplet.

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7
Q

Why is genetic code known as universal?

A

Each triplet codes for same amino acid in all organisms.

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8
Q

Why is genetic code known as non-overlapping?

A

Each base in the sequence is only read once.

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9
Q

How many bases are required to code for a chain of 6 consecutive amino acids?

A

18

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10
Q

Why might a change in 1 base result in an enzyme becoming non-functional?

A

Sequence of amino acid in polypeptide will be different.

Change in primary structure might result in different shaped tertiary structure.

Enzyme shape will be different and may not fit the substrate

Enzyme-substrate complex cannot be formed and so the enzyme is non-functional.

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11
Q

What is the main structure of eukaryotic chromosomes?

A 
DNA double helix
Nucleosome fibre
Solenoid fibre
Folded/coiled solenoid fibre
Super coiling
Chromosome
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12
Q

What is a histone?

A

Protein which together with DNA, make up chromosomes of eukaryotic cells.

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13
Q

When are chromosomes visible?

A

Only visible as distinct structures when a cell is dividing.

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14
Q

What is the solenoid fibre?

A

A tightly coiled structure formed from more histones.

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15
Q

What is a homologous chromosome?

A

A pair of chromosomes (one paternal, one maternal) that have the same gene loci.

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16
Q

What does haploid mean?

A

Cells that only contain a SINGLE COPY of each chromosome.

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17
Q

What does diploid mean?

A

Cells in which the nucleus contains two sets of chromosomes.

2n

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18
Q

What is the function of the protein found in chromosomes?

A

It fixes the DNA into position.

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19
Q

What is the difference between the DNA of a prokaryotic cell and eukaryotic cell?

A

Prokaryotic: DNA is smaller, circular and is not associated with proteins (no chromosomes).

Eukaryotic: larger, linear and associated with proteins/ histones to form chromosomes.

20
Q

What is a genome?

A

A complete set of genetic information in an organism.

21
Q

What is a proteome?

A

The entire set of proteins expressed by a cell.

22
Q

What are the 2 types of RNA?

A
  1. Messenger RNA (mRNA)

2. Transfer RNA (tRNA)

23
Q

What is a codon?

A

The sequence of 3 bases on mRNA that codes for a single amino acid.

24
Q

What is a triplet?

A

The sequence of 3 bases on DNA.

25
Q

What is the structure of Ribonucleic acid (RNA)?

A
  • Pentose sugar
  • Organic base (adenine [A], guanine [G], cytosine [C], uracil [U])
  • Phosphate group
26
Q

What are the features of Messenger RNA (mRNA)?

A
  • Single helix molecule
  • No base pairing within the molecule
  • Sequence decided by bases in DNA
  • Has coded information in codons
27
Q

What are the features of Transfer RNA (tRNA)?

A
  • Single stranded cloverleaf-shaped
  • Some base pairing (hydrogen bond)
  • Has an amino acid attachment site
  • Anticodon at other end complementary to codon in mRNA
28
Q

What is the difference between the structure of mRNA and tRNA?

A

mRNA: larger, greater variety of types, long single helix
tRNA: smaller, fewer types, clover-leaf in shape

29
Q

What are 3 differences between the molecular structure of RNA and DNA?

A 
RNA= single strand
DNA= double helix
RNA= ribose sugar
DNA= deoxyribose sugar
RNA= uracil replaces thymine
DNA= contains thymine
30
Q

What is the difference between a codon and anticodon?

A

Codon: triplet of bases on mRNA that codes for amino acid
Anticodon: triplet of bases on tRNA that is complementary to a codon

31
Q

What are some advantages of using mRNA rather than DNA for translation?

A

-Contains no introns
-Single stranded & linear: ribosomes move along strand which
tRNA binds to exposed bases

32
Q

What is transcription?

A

The production of mRNA from a DNA template strand.

33
Q

Where does transcription take place?

A

In the nucleus.

34
Q

What is the process of transcription?

A
  1. Hydrogen bonds are broken and DNA has unzipped using DNA helicase, the nucleotide bases are exposed.
  2. One strand of DNA acts as a template.
  3. Free RNA nucleotides match with complimentary base pairs from the promoter region (U replaces T).
  4. RNA polymerase catalyses the reaction to link nucleotides by forming phosphodiester bonds.
  5. Pre-mRNA is formed.
35
Q

What is splicing?

A

The removal of introns (non-coding regions) from pre-mRNA to produce mRNA.

36
Q

Where does splicing occur?

A

Only in eukaryotic cells before the mRNA passes into the cytoplasm via a nuclear pore.

37
Q

What are the enzymes involved in transcription and what do they do?

A

RNA polymerase: It moves along the template DNA strand, adding nucleotides one at a time, to build a strand of pre-mRNA.

38
Q

Why is splicing of pre-mRNA necessary?

A

Pre-mRNA has nucleotide sequences derived from introns.

Introns are non-functional and would leave to production of non-functioning polypeptides if left.

39
Q

What is translation?

A

-mRNA is used as a template to which complementary tRNA molecules attach.

-The amino acids they carry are linked to form a
polypeptide.

40
Q

What is produced by translation?

A

Proteins.

41
Q

Where does translation take place?

A

In the cytoplasm on the ribsosomes.

42
Q

What is the structure of a eukaryotic ribosome?

A

-Made up of a small and large sub-unit.

Small sub-unit: referred to as 40s sub-unit.
Large sub-unit: referred to as 60s sub unit.

43
Q

What is the process of translation?

A
  1. Small ribosomal subunit binds with mRNA
  2. tRNA molecule with matching anti-codon attaches to complementary base on the mRNA
  3. Large ribosomal subunit binds to mRNA to from translation initiation complex
  4. More tRNA anticodons attach to mRNA codons
  5. Amino acid attached to tRNA’s attach to one another by peptide bonds
  6. Amino acids form a long polypeptide chain
  7. tRNA releases amino acid to pick up more amino acids
44
Q

What is the role of tRNA in translation?

A

tRNA helps to ensure the correct sequence of amino acids in the polypeptide.

Attached amino acids at one end and has a sequence of 3 bases (anticodon) at the other end.

The anticodon on tRNA pairs with the complementary codon sequence on mRNA.

45
Q

How do organic bases help to stabilise the structure of DNA?

A
  • Hydrogen bonds

- Many hydrogen bonds provide strength

46
Q

What is the role of STOP codons?

A
  • Stop translation

- Detachment in polypeptide chain

47
Q

Define ‘non-coding base sequences’ and describe where the non coding multiple repeats are positioned in the genome?

A

DNA that does not code for protein positioned between genes

Biology (25 decks)

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