- one gene codes for one protein - eukaryotic genome

- one gene codes for more than one protein - prokaryotic genome

Topic 7 Flashcards by Allyssa L

translation is carried out on…

ribosomes

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mRNA read ….

5’ to 3’

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tRNA

allow for change in “language” (between mRNA and amino acids)

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how many possible amino acid encoding codons?

61 (+3 STOP)

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tRNA read….

3’ to 5’ (anticodon)

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aminoacyl tRNA

special tRNA with a specific amino acid covalently bound at 3’ end

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rRNA

serves both a structural and functional role; RNA components of ribosomal subunit

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anticodon is located on…

the tRNA

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______ ribosomes are more complex than_________ ribosomes.

eukaryotic, prokaryotic

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prokaryotic ribosomes

70S; 50S large, 30S small

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eukaryotic ribosomes

80S; 60S large, 40S small

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what makes up ribosomes?

protein and rRNA

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ribosomes are assembled where

nucleolus of nucleus

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describe ribosome assemble

ribosomal proteins are imported to nucleolus
they attach to pre-rRNA
pre-rRNA splits to two (large and small subunit)

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tRNAs are synthesized by…

RNA pol III

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__-shaped structure is critical for proper anticodon function

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3 steps of tRNA processing

produced through RNA processing

RNA cleavage
covalent addition of CCA
base modification (RNA editing)

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There are _____ different aminoacyl tRNA synthetase

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Each aminoacyl tRNA synthetase recognizes

correct amino acid

- correct codon on mRNA

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Three steps to “charge” a tRNA

activation of amino acid
addition of amino acid to tRNA
proper folding of tRNA which can bring amino acid to the ribosome

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What are the first 2 controls for specificity of amino acid incorporation into a protein?

matching correct amino acid to correct tRNA (specificity of enzyme)
correct base-pairing of codon and anticodon (specificity of base pairing)

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wobble hypothesis

some tRNAs can recognize more than one mRNA codon

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monocistronic

one gene codes for one protein

- eukaryotic genome

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plycistronic

one gene codes for more than one protein

- prokaryotic genome

3 stages of translation

- initiation - elongation - termination

signals for translation initiation in prokaryotes

-Shine-Dalgarno sequence

signals for translation initiation in eukaryotes

small ribosomal unit binds to 5' cap of mRNA and slide along until it finds start codon

initiation of translation in euk. part 1

40S ribosomal subunit + eIFs (eukaryote Initiation Factors) + charged tRNAmet assemble

initiation of translation in euk. part 2

- assembly from Step 1 meets up with a mature mRNA (poly AA tail + PABP and 5' cap) - and binds to its 5’m7G cap

initiation of translation in euk. part 3

Step 2 assembly starts at 5’m7G cap and scans mRNA for AUG start codon

initiation of translation in euk. part 4

- Entire complex dissociates from start site (except the 40S subunit and tRNAmet ), - 60S ribosomal subunit attaches

elongation stage involves which 3 tRNA binding sites?

- A (aminoacyl) site - P (peptidyl) site - E (exit) site

A (aminoacyl) site

arrival

P (peptidyl) site

pause

decoding centre

within small subunit; ensures proper aminoacyl tRNA pairs with codon

third step in specificity

decoding centre

elongation of translation step 1

tRNAmet is at start site from the cap

elongation of translation step 2

the next tRNA comes to A site

elongation of translation step 3

a peptide bond forms between the first two amino acids

elongation of translation step 4

ribosome moves downstream (A site to P site); translocation

elongation of translation step 5

repeat steps 2-4

termination of translation step 1

stop codon ends up in A site

termination of translation step 2

a releasing factor moves into A site

termination of translation step 3

poly-peptide chain released

termination of translation step 4

release factor causes ribosome to disassemble from mRNA

post-translational modification

chemical modification of a polypeptide chain after translation

chaperones

protein that keeps protein unfolded until completely synthesized and facilitates folding, but does not incorporate into complex

proteolysis or cleavage

important for maturation of several proteins

signal sequences

mature proteins that target proteins to specific cellular compartments

some enzymes and hormones require....... to create a functionally active protein

cleavage

types of post-translational modification

- phosphorylation - glycosylation - lipid addition - ubiquitylation

phosphorylation

small molecules such as phosphate added to regulate protein activity

glycosylation

carbohydrate addition to form glycoproteins

lipid addition

lipid addition to form lipoproteins

ubiquitylation

addition of ubiquitin polypeptide to target proteins for degradation

unlike protein cleavage, PTMs are....

reversible

What processes can ultimately regulate the level of a protein in the cell?

regulation of degradation

autpophagy

protein degradation by lysosomes