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biology > D1.2 - protein synthesis > Flashcards

D1.2 - protein synthesis Flashcards

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1
Q

allele

A

form of a gene which differs from other versions by one or a few bases

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2
Q

gene

A

section of DNA that codes for a protein

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3
Q

non-template strand

A

strand of DNA not used in transcription that has a complimentary base sequence to the template strand

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4
Q

somatic cell

A

a body cell that is not a gamete

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5
Q

template strand

A

strand of DNA used for transcription of a particular gene

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6
Q

triplet

A

group of 3 bases in DNA that code for an amino acid or a stop signal to terminate translation

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7
Q

transcription

A

synthesis of mRNA using a DNA template
- first stage of gene expression where genes can be switched on or off

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8
Q

what is the sequence of mRNA determined by?

A

order of the base sequence of the gene being transcribed

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9
Q

what is the process of transcription?

A
  1. in the nucleus, DNA is unwound and strands are separated by RNA polymerase breaking H bonds
  2. RNA polymerase causes new RNA nucleotides to be attached to the template strand of DNA using complementary base pairing which are linked together by phosphodiester bonds into a strand of mRNA
  3. mRNA detaches from the DNA template strand when the terminator sequence has been reached
  4. mRNA molecule moves out of the nucleus to a ribosome in the cytoplasm
  5. DNA rewinds
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10
Q

how do new RNA nucleotides bind to the template strand of the DNA?

A

hydrogen bonding between the DNA and RNA bases

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11
Q

what can single DNA strands be used as a template for?

A

single DNA strands can be used as a template for transcribing a base sequence without the DNA base changing

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12
Q

why does transcription occur frequently in somatic cells?

A

to conserve DNA base sequences as somatic cells don’t divide and DNA replication doesn’t occur

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13
Q

what happens to genes during protein synthesis?

A

genes are expressed but not all genes in a cell are expressed in a given time
- allows genetically identical cells within an organism to gain specialised structures and functions via differentiation

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14
Q

translation

A

synthesis of polypeptides from information encoded in mRNA which is translated into an amino acid sequence

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15
Q

what is the role of mRNA?

A

messenger RNA - carries information from a gene within the DNA to a ribosome in the cytoplasm
- binds to small sub-unit of a ribosome and determines the amino acid sequence of the protein

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16
Q

what is the role of ribosomes?

A
  • where translation occurs to synthesise polypeptides
  • contain protein and catalytic RNA
  • binds mRNA via small sub-unit
  • binds 2 tNRA via large sub-unit
17
Q

what is the role of tRNA?

A

transfer RNA
- carries a specific amino acid to the ribosome according to the base sequence

18
Q

what happens when 2 tRNA molecules bind simultaneously to the large sub-unit of a ribosome?

A

hold the amino acids in place while the ribosome catalyses the condensation reaction to form a peptide bond

19
Q

codon

A

a sequence of 3 bases on an mRNA molecule that codes for one amino acid

20
Q

anti-codon

A

a sequence of 3 bases on a tRNA molecule that binds to the corresponding codon through complementary base pairing

21
Q

what are the 3 key features of the genetic code

A
  • triplet code
  • denegeracy
  • universality
22
Q

genetic code

A

how the sequence of bases in DNA determines the sequence of amino acids and resulting proteins

23
Q

what is the triplet code and what are the evaluations?

A

a group of 3 bases is sufficient to code for amino acids as there are 64 combinations

24
Q

what is universality?

A

all organisms share the same genetic code, with the same codons coding for the same amino acids and the conservation of genetic code across all forms is evidence of the universal common ancestor

25
Q

what are the positives of universality?

A

allows genes to be transferred to other species during genetic engineering
- human insulin gene can be inserted into bacterial cells to produce human insulin proteins for use in diabetes treatment

26
Q

what are the negatives of universality?

A

slightly different meaning of some codons, meaning the genetic code isn’t universal
- differences occurred after the common origin of life

27
Q

what is degeneracy?

A

some amino acids are coded for by more than one codon
- some point mutations will have no impact on the amino acid and the protein synthesised

28
Q

codon table

A

used to deduce the sequence of amino acids coded by an mRNA strand
- can be stop or start codons

29
Q

how is the codon table read?

A

left side, top side, middle

30
Q

where does translation occur?

A

ribosomes in the cytoplasm

31
Q

what is the process of translation?

A
  1. small subunit of ribosome binds to the start codon at the start of the mRNA sequence
  2. tRNA molecules transfer a specific amino acid to the large sub-unit of the ribosome due to complementary base pairing between the codon and anti-codon
  3. the ribosome moves along the mRNA sequence, linking amino acids by peptide bonding to grow a polypeptide chain
  4. elongation process continues in a cycle
  5. stop codon is reached, the tRNA and mRNA molecules dissociate and release the polypeptide which folds into a unique shape for its function
32
Q

mutation

A

permanent change in the DNA base sequence

33
Q

point mutation

A

replacement of a nucleotide base with another

34
Q

what is the consequence of a point mutation?

A
  • once base on the DNA is changed
  • changes the triplet
  • during transcription, different codon is produced within the mRNA
  • may code for another amino acid
  • can change the 3D conformation of a protein
  • protein will have a different function
35
Q

sickle cell anaemia

A

genetic condition caused by a point mutation in the gene for one of the sub-units of haemoglobin

36
Q

how does the point mutation affect the haemoglobin beta chain protein structure in sickle cell anaemia?

A
  1. thymine is replaced with adenine in the DNA
  2. triplet in the non-template strand changes from GAG to GTG
  3. triplet on the template strand changes from CTC to CAC
  4. codon in the mRNA changes from GAG to GUG
  5. glutamic acid is replaced by valine amino acid in the polypeptide chain
  6. affects the 3D conformation of the haemoglobin protein as it now has a sickle shape
37
Q

what are the consequences and symptoms of sickle cell anaemia?

A

distorted haemoglobin causes the sickling shape of erythrocytes, which block the capillaries and hinder blood flow
fatigue due to red blood cells not carrying enough oxygen, risk of death and anemia

38
Q

what happens if a person is heterozygous for sickle cell anemia?

A

one allele which codes for a non-sickle protein and one allele that codes for a sickle protein
- have a milder form of sickle cell anaemia and some resistance to malaria

biology (28 decks)

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