D1.2 Protein Synthesis

Question 1

Name 3 forms of RNA (3)

Answer 1

mRNA

rRNA

tRNA

Question 2

Define mRNA (2)

Answer 2

messenger RNA made as a complementary strand to one DNA strand

copy of other DNA strand + contains uracil

Question 3

Define rRNA (2)

Answer 3

ribosomal RNA found in ribosomes

decodes mRNA into amino acids

Question 4

Define tRNA (2)

Answer 4

transfer RNA carries amino acids to ribosomes

bonded together to form polypeptides

Question 5

Features of Transcription (4)

Answer 5

first step for cell to build protein

production of RNA (mRNA) using DNA as template

transcription takes place in nucleus in eukaryotic cells

transcription takes place cytoplasm for prokaryotes

Question 6

Stages of transcription (3)

Answer 6

DNA strands separated into 2 stands + RNA polymerase binds to DNA strand

RNA polyemrase builds mRNA on one of strands (complementary to template strand/antisense strand)

terminator sequence (“stop” codon) in DNA reached + mRNA detached

Question 7

Define the template strand/antisense strand for DNA (2)

Answer 7

strand with directionality 3’ to 5’

strand connected to mRNA

Question 8

Define triplet for DNA

Answer 8

group of 3 bases for DNA

Question 9

Define codons for DNA

Answer 9

group of 3 bases for mRNA (complementary to DNA triplet)

Question 10

Features of translation (3)

Answer 10

only genes transcribed into mRNA are translated into proteins

mRNA moves out of nucleus via nuclear pore once transcribed

mRNA combines with ribosome in cytoplasm

Question 11

Process of translation (5)

Answer 11

mRNA attaches to ribosome at start codon (AUG)

tRNA with complementary anticodon (UAC) attaches to mRNA

tRNA attached to amino acid (methionine)

ribosome moves along mRNA + brings 2 tRNA molecules at any one time

enzyme + ATP used to join amino acids with peptide bond

Question 12

Why bases are complementary to each other

Answer 12

complementary bases form hydrogen bonds with each other but not with other bases

Question 13

Directionality of transcription

Answer 13

3’ to 5’

Question 14

Features of mRNA in translation (4)

Answer 14

has site for ribosome to bind to

has sequence of codons which codes for specific amino acids

has start + stop codon to indicate when translation will stop/start

mRNA can be translated multiple times but is broken down if it is damaged or if polypeptide it codes for is no longer needed

Question 15

Features of tRNA (transfer RNA) in translation (4)

Answer 15

translates base sequence of mRNA in to amino acid sequence

tRNA has anticodon at one end + attachment point at other end for amino acid corresponding to anticodon

transfers corresponding amino acid to end of growing polypeptide once code on mRNA recognised

tRNA has specific corresponding amino acid attached

Question 16

Shape of tRNA (3)

Answer 16

single-stranded RNA molecule

folds on itself to form clover-leaf structure

with double stranded regions + 3 hairpin loops

Question 17

Features of ribosomes in translation (4)

Answer 17

acts as enzyme to form peptide bonds between amino acids

complex structure of small + large subunit

small subunit binds to mRNA

large subunit has 3 binding sites for tRNA

Question 18

Define an anticodon

Answer 18

3-base code complementary to the matching RNA codon

Question 19

Stages of translation (3)

Answer 19

initiation

elongation

termination

Question 20

Elongation stage of translation (5)

Answer 20

ribosome moves along mRNA, one codon at a time

as each codon moves into place, new tRNA carries corresponding amino acid,

attaches + moves previous tRNA molecules to the next position

new amino acids are delivered = condensation reactions catalysed + peptide bonds formed

repeats until termination codon reached

Question 21

Directionality of translation

Answer 21

5’ to 3’ direction

Question 22

Define a promoter (3)

Answer 22

section of DNA that initiates gene transcription

proteins known as transcription factors bind to promotor-

act as binding point for RNA polymerase enzymes that catalyse transcription

Question 23

Importance of transcription factors (2)

Answer 23

binding of correct transcription factors –> allows the RNA polymerase to also bind + begin to transcribe the DNA into RNA.

transcription factors are missing or cannot bind to the promoter = transcription will not take place and that gene cannot be expressed

Question 24

Features of non-coding genome (3)

Answer 24

98% of the human genome

DNA sequences within genome that do not have information to make protein.

not represented within the amino acid sequence of expressed proteins.

Question 25

Regions of non-coding DNA (4)

Answer 25

regulators of gene expression introns telomeres genes for tRNA + rRNA

Question 26

Define regulators of gene expression (4)

Answer 26

promoters DNA sequences that are binding sites for proteins e.g enhancers + silencers enhancers - increase rate of transcription silencers - decrease rate of transcription

Question 27

Define introns

Answer 27

DNA base sequences in eukaryotic genes that are removed at end of transcription

Question 28

Define telomeres (3)

Answer 28

repetitive sequences that protect ends of chromosome. ensure that DNA is replicated correctly every cell division = telomeres lose short stretches of DNA

Question 29

Features of post-transcriptional modification (3)

Answer 29

mRNA must be prepared for translation genes contain non-coding information --> must be removed only for eukaryotes

Question 30

Procedure of post-transcriptional modification (5)

Answer 30

transcription - synthesis of pre-mRNA addition of a 5' cap + poly-A tail - protect the mRNA molecule from degradation by stabilising ends 5' cap = modified nucleotide added to 5' end of RNA poly-A tail - 100-200 adenine molecules added to 3' of RNA splicing - removes (excises) introns and joins (ligates) exons to form mature mRNA.

Question 31

Define alternative splicing (2)

Answer 31

gene can be spliced in multiple ways by combining different exons and omitting others creates different versions of proteins with different functions

Question 32

Define initiation stage of translation (6)

Answer 32

Translation starts - 5' terminal of mature mRNA binds to small ribosomal subunit at mRNA binding site all mRNA have start codon (AUG) which can be linked to the initiator tRNA This specific tRNA always carries methionine - all proteins start with this amino acid ribosome moves along mRNA until it finds the start codon anticodon of the initiator tRNA (amino acid methionine) binds to codon of the mRNA large ribosomal subunit joins

Question 33

Features of post-translational modification (3)

Answer 33

polypeptides synthesised by ribosomes on the rough endoplasmic reticulum are packaged in vesicles vesicles carry polypeptides to the Golgi apparatus. modifications carried out in Golgi apparatus

Question 34

Recycling of amino acids by proteasomes

Answer 34

unneeded/damaged proteins can be broken down + recycled for amino acids carried out by proteasome (protein complex) hydrolyses proteins by breaking the peptide bonds between amino acids

Question 35

Function of recycling amino acids by proteasomes (3)

Answer 35

proteome = total proteins made within body production of proteins + large supply of amino acids needed to maintain proteomes provides amino acids to do this