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h2 bio > dna genomics ll (translation and transcription) > Flashcards

dna genomics ll (translation and transcription) Flashcards

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Biology 101 flashcards
1
Q

what is a gene

A

specific sequence of nucleotides in a DNA molecule which codes for a specific sequence of amino acids in one polypeptide chain

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2
Q

features of the genetic code

A
  1. it is a universal code
  2. it is a degenerate code (more than one codon codes for the same amino acid)
  3. it is a non-overlapping code
  4. it is a continuos code
  5. it is a triplet code
  6. it includes start and stop codons
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3
Q

components of a gene

A

promoter
termination sequence
transciption unit

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4
Q

definition of transcription

A

process where by the nucleotide sequence of a gene is used as a template to direct synthesis of RNA made up of complementary base sequences

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5
Q

function of promoter

A

DNA sequences that function as a recognition site for binding of RNA polymerase and regulatory proteins to initiate transcription

determine which one of the 2 strands of DNA molecule is used as a template for transcription

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6
Q

events of transcription

A

initiation
elongation
termination
post transciptional modfication

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7
Q

what happens in initiation (transcription)

A
  1. RNA polymerase attaches to promoter with the aid of protein factors
  2. RNA polymerase breaks hydrogen bonds between complementary base pairs = unzipes and separates the two strands of the DNA helix
  3. only one strand, with promotor, is used as the template to synthesise complementary mRNA strand
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8
Q

what happens in elongation

A
  1. free ribonucleotides will bind to deoxyribonucleotides on DNA template strand by complementary base pairing
  2. adenine forms 2 hydrogen bonds with uracil, thymine forms 2 hydrogen bonds with adenine, cytosine forms 3 hydrogen bonds with guanine
  3. RNA polymerase catalyses formation of phosphodiester bonds between adjacent ribonucleotides = form sugar-phosphate backbone of growing mRNA
  4. mRNA strand is synthesised in 5’ to 3’ direction as new ribonucleotides are added to 3’ OH end of growing mRNA strand
  5. as RNA polymerase continues down the template strand, region of DNA that has just beem transcribed reanneals
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9
Q

what occurs in termination

A

after RNA polymerase transcribes through the termination sequence, the mRNA chain is released and the RNA polymerase will dissociate to terminate transcription

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10
Q

what happens in post transciptional modification

A
  1. addition of 5’ cap
  2. RNA splicing
  3. polyadenylation
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11
Q

what happens in addition of 5’cap

A

cap of a methylated guanosine nucleotide will be added to the 5’ end of the pre-mRNA

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12
Q

what happens in RNA splicing

A

by a spliceosome, intron sequences are excised out and the exons are joined together to form the mature mRNA

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13
Q

what happens in polyadenylation

A
  1. pre-mRNA is cleaved by an endonuclease 10-35 nucleotides downstream of the polyadenylation signal = AAUAA sequence
  2. poly-A-polymerase adds many adenine nucleotides downstream of the signal
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14
Q

what is the function of mRNA

A
  1. takes information out of the nucleus via the nuclear pore to the cytoplasm where translation takes place
  2. acts as template for translation
  3. sequence of codon within coding region of mRNA determines polypeptide sequence
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15
Q

what are the functions of tRNA

A

bring in specific amino acids in a sequence corresponding to sequence of codons in mRNA to growing polypeptide
facilitates translation by
1. its ability to bind to a specific single amino acid during amino acid activation
2. the ability of its anticodon to base-pair with mRNA codon during translation

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16
Q

what is the least number of different tRNAs that should exist in any cell

A

at least 20 different tRNAs, each corresponding to 1 of the 20 different amino acids

17
Q

function of rRNA

A
  1. associates with a set of proteins to form ribosomes
  2. main constituent of the interface between the large and small subunits of ribsome: allows mRNA to bind to small ribosomal unit by complementary base pairing between the rRNA in the mRNA binding site in small ribosomal unit and mRNA
  3. main constituent of the P and A site on large ribosomal subunit: enables binding of aminoacyl-tRNAs to P and A site by complementary base pairing
  4. part of rRNA molecule on large ribosomal subunit acts as ribozyme peptidyl transferase, catalysing formation of peptide bond between 2 amino acids
18
Q

what are teh different sites in the large subunit of the ribosome

A

aminoacyl site: holds incoming tRNA carrying next amino acid to be added
peptidyl site: holds tRNA carrying the growing polypeptide chain
exit site: where tRNA leaves the ribosome

19
Q

define translation

A

process by which a sequence of ribonucleotides in an mRNA molecule is used as a template to synthesize a sequence of amino acids in a polypeptide chain

20
Q

what are the events of translation

A
  1. initiation
  2. codon recognition
  3. peptide bond formation
  4. translation
  5. termination
21
Q

what happens before translation for it to occur

A

amino acid activation
a specific amino acid is covalently attached to the 3’ CCA stem of a specific tRNA with a specific anticodon to form a aminoacyl tRNA
catalysed by a specific aminoacyl-tRNA synthetase

22
Q

how is tRNA activated with the correct amino acid

A
  1. there are 20 different aminoacyl tRNA synthetases, one for each amino acid
  2. the enzyme have specific active sites that are complementary in shape and charge to specific amino acid and the different tRNAs through their specific acitve sites at their acceptor stem and/or anticodon loop of the specific tRNA molecule
23
Q

what happens in initiation

A
  1. translation initiation factors will facilitate binding of small ribosomal subunit and initiator tRNA carrying methionine to newly synthesised mRNA strand
  2. anticodon UAC of initiator tRNA will complementary base pair with start codon AUG of mRNA
  3. binding od large ribosomal subunit will complete ribosome forming translational initiation complex
    4.formation of complex positions initiator tRNA at P side, leaving A site vacant for incoming aminoacyl-tRNA molecules
24
Q

what happens in codon recognition

A

a second aminoacyl tRNA with a specific anticodon and corresponding amino acid complementary base pairs with a specific mRNA codon at the A site by forming hydrogen bonds

25
Q

what happens in peptide bond formation

A
  1. a peptide bond is formed between adjacent amino acids, catalysed by peptidyl transferase on the large ribosomal subunit
  2. methioine dissociates from initiator tRNA
  3. methioine remains bound to second amino acid at A site
26
Q

what happens in translocation

A
  1. ribosome translocates in 5 to 3 direction, shifting first tRNA to E site and allowing it to be released into cytosol
  2. tRNA with growing polypeptide chain is now at P site
  3. A site will hold a new incoming aminoacyl tRNA with an anticodon complementary to next codon on mRNA
  4. process repeats until a stop codon is reached
27
Q

what happens in termination

A
  1. termination begins when stop codon reaches A site
  2. release factors will enter A site, causing hydrolysis of covalent ester bond between polypeptide chain and tRNA in P site
  3. polypeptide is released from ribosome and will fold into its secondary and tertiary structures
  4. ribosome dissembles into its subunits
28
Q

what are the stop and start codons

A

start: AUG
stop: UAA/UAG/UGA

h2 bio (19 decks)

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