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BMSC 220 > Chapter 6 > Flashcards

Chapter 6 Flashcards

1
Q

What are proteins?

Are they strict on how they must be made?

A

Active players in most cell processes
Implement the myriad tasks that are directed by the info encoded in genomic DNA
Synthesized from mRNA template in translation
That is highly conserved throughout evolution

Must be made with correct amino acid sequence, right place, right amount, right shape, right time, right modifications

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2
Q

How is translation carried out?

A

In the ribosomes
With transfer RNAs serving as adaptors between mRNA template and amino acids turning to protein
Used a genetic code (triplet code)
mRNA read 5’ to 3’
First amino acid is always methionine (AUG)

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3
Q

What are the possible combos of amino acid code on the genetic code table?
What are the number of different amino acids on the genetic code table?

A

61 possible amino acid encoding codons in triplet code
3/64 codons are stop and 1 start codon
There are 20 different amino acids

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4
Q

What is aminoacyl tRNA and how codons and anticodons work in translation?

A

Aminoacyl tRNA is the tRNA with a specific amino acid covalently bound at 3’ end
Codons on mRNA base pair with anticodons on tRNA codon
mRNA 5’ to 3’
tRNA 3’ to 5’
Picture on slide 13

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5
Q

What rRNAs?

What are pre-rRNAs?

A

Components of ribosomes
Form complex 3D secondary structures highly conserved (intramolecular base pairing allows complex secondary structure slide 18)
Numerous ribosomal subunits associate with the rRNA to form a ribosomal subunit
Pre-rRNA is the primary transcript of RNA polymerase I that is cleaved to form individual ribosomal RNAs (28S, 18S, 5.8S)
Picture on slide 16

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6
Q

How do the eukaryotic and prokaryotic ribosomes differ?

A

Very similar but:
Prokaryotic is a 70S ribosome and eukaryotic is a 80S ribosome
Look at slide 17 to see differences in make ups
slide 19 to see pic of ribosome

Ribosomes= protien + rRNA

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7
Q

Where are ribosomes assembled?

A

Within the nucleolus of the nucleus
They are imported to the nucleolus then attached to the pre-rRNA then the pre rRNA splits in two; one part becomes the 40S and another becomes the 60S

The end products of transcription by RNA polymerase I (5.8S,18S,28S), II (ribosomal proteins), III (5S rRNA) all form parts of the fully assembled ribosome

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8
Q

What are transfer RNAs?

A

Synthesized by RNA polymerase III
Possess 3 unique nucleotide identifying sequences (antidcodons) that allow correct amino acid to be aligned with appropriate codon in mRNA
Cloverleaf structures based on intramolecular base pairing (hybridization)
Structure on slide 24

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9
Q

What are aminoacyl tRNA synthetases?
How many different ones are there?
What are the three steps to charge a tRNA?

A

20 different aminoacyl tRNA synthetases that each recognize the correct amino acid and the tRNA
3 steps to charge:
1. Activation of amino acid
2. Addition of amino acid to tRNA
3. Proper folding of tRNA which can bring amino acid to the ribosome
Slide 25

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10
Q

What are the two points for specificity of amino acid incorporation into a protein during translation at the tRNA level?

A
  1. Matching correct amino acid to correct tRNA (specificity of enzyme)
  2. Correct base pairing of codon and anticodon
    (Specificity of base pairing)
    Slide 26

The first and second bases of each triplet codon confer the most specificity for which amino acid the triplet will code

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11
Q

What causes wobble?

A

There are approx 40 different tRNAs and 20 different amino acids so many amino acids have more than one triplet code that code for it which creates wobble

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12
Q

What does monocistronic mean compared to polycistronic?

A

Monocostronic- one gene codes for one protein
Eukaryotic genome
Polycistronic- one gene coded for more than one protein
Prokaryotic genome
Picture on slide 31

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13
Q

What are the three stages of translation?

A

Initiation
Elongation
Termination

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14
Q

What are the signals for translation initiation in prokaryotes vs eukaryotes?

A

Prokaryotes- an mRNA sequence called shine-dalgarno sequence binds to complementary base pairs in 16S rRNA
Eukaryotes- a small ribosomal subunit (40S) binds to 5’ m7G cap of the mRNA and the 40S+ initiation complex slides along the mRNA until it finds the start codon
Slide 35

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15
Q

What are the steps in translation initiation?

A

Step 1- 40S ribosomal subunit, various initiation factors (eiFs) and charged tRNA assemble (charged tRNA binds to 40S BEFORE 40S binds to mRNA
Step 2- 40S/tRNA/eIF complex meets with mature mRNA and binds to 5’ m7G cap
Step 3- entire complex slides along mRNA until it finds AUG start codon
Step 4- Most of complex (except 40S/tRNA) dissociates from the start site and 60S ribosomal subunit attaches
Slides 38-42

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16
Q

What must mRNA have to bind the 40S/tRNA/eIF complex?

A

Must have both a 5’ m7G cap and 3’ polyAAAA tail

Slide 40 picture

17
Q

What are the three adjacent tRNA binding site in the ribosome involved in the elongation stage of translation?
What is the deciding centre?

A

A (aminoacyl) site: Arrival
P (peptidyl) site: Pause (polypeptide)
E (exit) site- Exit

Slide 45 picture

Decoding center within small 40S ribosomal subunit ensures proper aminoacyl tRNA pairs with codon
(3rd step in specificity)

18
Q

What are the 5 steps of elongation in translation?

A
  1. tRNA/ribosome complex sits at AUG start site of mRNA
  2. Next charged tRNA comes to A site
  3. Peptide bond formation between amino acids
  4. Ribosome moves downstream (tRNA moves from A site to P site
  5. Repeat steps 2-4
    Slides 46-50
19
Q

What are the 4 steps of termination of translation?

A
  1. Stop signal (codon) in A site (UAA)
  2. Releasing factor in A site (sits at UAA codon)
  3. Polypeptide chain released
  4. Ribosome disassembly (release factor causes structure to come apart) ribosomal subunits can be reused
    Slides 52-56
20
Q

Do ribosomes make proteins?

A

FALSE

21
Q

What is post-translational modification (PTM)?

And explain why polypeptides must fold.

A

PTM: chemical modification of a polypeptide chain after translation

To be useful, polypeptides must fold into district 3D conformations (secondary and tertiary structure) and multiple polypeptides must be assembled (quaternary structure) into a functional complex

22
Q

How does protein fold?

A

The amino acid sequence of a protein contains all the info required for a protein to fold into the correct 3D shape

23
Q

What are molecular chaperones?

A

Keep immature proteins in line (like human chaperones)
Don’t tell protein how to fold, just waist in folding properly
Keep protein unfolded till synthesized properly
Keep protein from incorrectly associating with other proteins
Slide 60 and 61

24
Q

What is cystic fibrosis?

A

Occurs due to mutation in the CFTR protein which deletes a single critical amino acid that disrupts the proteins ability to bind chaperones proteins in the ER=misfolding

Results in reduction of chlorine ions transported across plasma

25
Q

What is protein cleavage?

A

Proteolysis or cleavage of a polypeptide is important for maturation of proteins
Removal of first methionine is common
Signal sequences on amino terminus of polypeptide ms are cleaved to form a mature protein

26
Q

What are the four types of post-translational modification (PTM)?

A

Phosphorylation- small molecules (phosphate) added to protein activity
Glycosylation- carbohydrate addition to form glycoproteins (important for protein folding, cell to cell recognition)
Lipid addition- lipid addition to form lipoproteins (anchor proteins into membrane)
Ubiquitination (ubiquitylation)- addition of ubiquitin polypeptide to target proteins for degradation

27
Q

How is the level of proteins in a cell regulated?

A

Regulation of the amount of proteins in the cells is controlled at the level of transcription and translation (determines the amount of any enzyme or protein that is synthesized by the cell and how quickly a protein degrades)

28
Q

What is protein degradation?

A

Half lives of proteins can vary from minutes to days
Rapid degradation allowed cells to quickly adapt to outside stimuli
Faulty proteins are recognized and quickly degraded within cells

29
Q

What are the two major pathways of protein degradation?

A

Ubiquitin-proteasome pathway- ubiquitin is a PTM that targets cytosolic and nuclear proteins
Proteasomes are large protease complexes that recognize and degrade polyubiquinated proteins
Lysosomal proteolysis- lysosomes degrade, contain digestive enzymes including proteases
Autophagy is protein degradation by lysosomes

BMSC 220 (12 decks)

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