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biology > protein synthesis > Flashcards

protein synthesis Flashcards

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1
Q

what 2 stages does protein synthesis occur in?

A

translation and transcription

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2
Q

what is transcription?

A

DNA is transcribed and an mRNA molecule is produced

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3
Q

where does transcription occur in?

A

the nucleus of the cell

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4
Q

what is the role of transcription?

A

produce an mRNA copy of a gene

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5
Q

what is the first stage of transcription?

A

1) the two strands of the DNA helix are unzipped by breaking the weak hydrogen bonds between complementary base pairs

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6
Q

what is the unwinding of the helix caused by?

A

an enzyme (helicase)

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7
Q

what does the unwinding of the helix cause? (the second stage)

A

this exposes the template strand of the gene that codes for the protein being synthesised

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8
Q

what does the enzyme RNA polymerase attach to? (second stage)

A

attaches to the DNA just before the gene

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9
Q

what do the mRNA nucleotides do (3rd stage)?

A

free mRNA nucleotides that are present in the nucleus bind to and form hydrogen bonds with exposed complementary nucleotides on the template strand by complementary base pairing

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10
Q

4th step of transcription?

A

RNA polymerase then catalyses the formation of covalent bonds between the RNA nucleotides to form a strand of mRNA

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11
Q

what bases do RNA nucleotides contain?

A

the same as DNA, except the T is replaced by U- U base pairs with A

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12
Q

why is mRNA a complementary copy?

A

because the opposite base bonds with the exposed DNA bases, the strand of mRNA is an opposite copy of the DNA strand (except that U replaces T)

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13
Q

where does the newly formed strand of mRNA leave via?

A

leaves the nucleus via a pore in the nuclear envelope and travels to the ribosomes

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14
Q

what does DNA contain?

A

the information to make a protein

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15
Q

what code for a specific amino acid?

A

three bases (a codon)

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16
Q

what is the sequence of bases?

A

a set of instructions for which order to join amino acids in to make a protein

17
Q

where are proteins synthesised?

A

in the cytoplasm

18
Q

what is tRNA?

A

carrier molecules

19
Q

how many different naturally-occurring amino acids are there?

A

about 20

20
Q

how many amino acids does each protein molecule have?

A

hundreds or even thousands of amino acids joined together in a unique sequence

21
Q

where does translation occur?

A

in the cytoplasm of the cell

22
Q

what is the end result of translation?

A

the production of a chain of amino acids that will go on to form a protein

23
Q

what is the first stage of translation?

A

once the mRNA molecule leaves the nucleus, it travels through the cytoplasm and attaches to the ribosome

24
Q

what is the second stage of translation?

A

in the cytoplasm, there are free molecules of tRNA- these tRNA molecules have a triplet of unpaired bases at one end known as the anticodon and the amino acid at the other end - each specific anticodon corresponds to a specific amino acid

25
Q

what is a codon?

A

every three bases on mRNA

26
Q

what is an anticodon?

A

the complementary 3 bases on the tRNA

27
Q

for every 3 mRNA bases…

A

the ribosome lines up one complementary molecule of tRNA

28
Q

what is the triplet code?

A

because there are 3 mRNA bases for each tRNA molecule

29
Q

what is the 3rd stage of translation?

A

the anticodon on each tRNA molecule pairs with a codon on the mRNA molecule- bringing its specific amino acid with it
tRNA molecules transport specific amino acids to the ribosome
the ribosome allows two tRNA molecules to sit next to eachother

30
Q

what is the 4th stage of translation?

A

the ribosome catalyses the formation of a covalent bond (peptide bond) between the two amino acids

31
Q

what is the 5th stage of translation?

A

used tRNA molecules exit the ribosome and collect another specific amino acid

32
Q

what is the 6th stage of translation?

A

this process continues until a stop codon on the mRNA molecule is reached- acts as a signal for translation to stop and the amino acid chain coded by the mRNA molecule is complete

33
Q

how is a polypeptide formed (6th step in translation)?

A

a chain of several hundred amino acids forms in the correct order according to the original DNA is then made- a polypeptide

34
Q

what happens to the polypeptide after translation?

A

it is finally folded into the correct shape and becomes a protein molecule e.g. an enzyme or an antibody

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