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BIOLOGY-FY > S1-L8: Protein Synthesis > Flashcards

S1-L8: Protein Synthesis Flashcards

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1
Q

What is the transcription process and how does it occur? (refer to figure 1)

A
  • RNA polymerase breaks DNA strand apart
  • single mRNA strand transcribed from template strand via single base pair ruling
  • In mRNA nucleobase T substituted by U
  • required nucleotides for mRNA synthesis found free in nucleus
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2
Q

Outline what pre-mRNA capping is (figure 2)

A
  • early mRNA (pre-mRNA) not in final form
  • pre-mRNA needs 5’ cap
  • ->cap composed of phosphorylated 7-methyl guanosine which added to 5’ end of mRNA guanyl transferase
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3
Q

Why is pre-mRNA capping important?

A
  • ensures mRNA transported out of nucleus
  • blocks degradation of mRNA by 5’ exonucleases
  • promotes translation
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4
Q

What is polyadenylation of pre-mRNA? (figure 3)

A
  • pre-mRNA needs 3’ poly-A-tail
  • pre-mRNA cleaved (split) by endonuclease near signal AAUAAA sequenced at 3’ end
  • ->approx. 200 adenosine residues then added at cleavage site by poly-A-polymerase
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5
Q

In appropriate detail explain the importance of polyadenylation

A
  • this poly-A-tail protects mRNA from degradation by 3’ exonucleases
  • poly-A-tail also aids in termination of transcription/ ensures export from nucleus AND important in translation
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6
Q

What is pre-mRNA splicing? (refer to figure 4)

A
  • pre-mRNA contains exons (code for proteins) AND sequences not coding for proteins (introns)
  • ->introns need to be spliced out to produce final mRNA
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7
Q

Define alternative splicing

A

-alternative splicing of pre-mRNA sequence able to produce different proteins of same gene

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8
Q

Outline the composure of mature mRNA (refer to figure 5)

A
  • 5’ cap
  • 5’ UTR (untranslated) region
  • coding region- to be translated in to protein
  • 3’ UTR region
  • poly (A) tail
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9
Q

What is the composition of a protein? (figure 6)

A

-consists of amino acids covalently linked into polypeptide chain

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10
Q

Which amino acids fall in to each of the following categories?: (refer to figure 7)

1-small
2-nucleophilic 
3-hydrophobic
4-aromatic 
5-acidic 
6-amide 
7-basic
A

1-Glycine (Gly)/ Alanine (Ala)
2-Serine (Ser)/ Threonine (Thr)/ Cysteine (Cys)
3-Valine (Val)/ Leucine (Leu)/ Isoleucine (Ile)/ Methionine (Met)/ Proline (Pro)
4-Phenylamine (Phe)/ Tyrosine (Tyr)/ Tryptophan (Trp)
5-Aspartic acid (Asp)/ Glutamic acid (Glu)
6-Asparaginine (Asn)/ Glutamine (Gln)
7-Histidine (His)/ Lysine (Lys)/ Arginine (Arg)

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11
Q

How is the specific order of amino acids in protein encoded in DNA/mRNA? (refer to figure 8)

A 
1-coding of DNA & template DNA
2-transcription of template DNA 
3-mRNA formed 
4-translation of mRNA 
5-peptide formed
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12
Q

How are amino acids represented by DNA?

A

-DNA base triplets represent each amino acid

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13
Q

Define a codon

A

-base triplets in mRNA called codons

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14
Q

State the number of amino acids AND mRNA codons there are

A
  • 20 amino acids

- 64 (4^3) mRNA codons

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15
Q

Define the term degenerate to describe the genetic code

A

-more than one codon codes for each of 20 amino acids

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16
Q

Why are the first two bases in codons most crucial?

A
  • possibly give tolerance against mutations

- example: UCA/UCC/UCG/UCU all code for serine

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17
Q

How do some mRNA codons have special roles? (figure 9)

A
  • start codon- AUG (methionine)

- stop codon- UAG/UAA/UGA

18
Q

What determines the sequence of amino acids in proteins?

A

-order of bases in genetic code in DNA codes for appropriate sequence of amino acids in proteins

19
Q

Outline the two important processes in protein synthesis

A
  • transcription (DNA to RNA)

- translation (RNA to protein)

20
Q

Briefly explain what substitution means and its possibly effect (refer to figure 10)

A
  • of bases changing codon can change corresponding amino acid
  • ->this may change protein structure significantly AND possibly result in stop codon being created in wrong place
21
Q

How may mutations in sickle cell anaemia occur? (figure 11)

A
  • DNA sequence- T substituted with A and A substituted with T
  • ->amino acid changes from glutamic acid to valine (mutant)
  • ->amino acid sequence changes
22
Q

What is the effect of the change in the amino acid sequence to the red blood cells?

A
  • change in amino acid sequence causes hemoglobin to cyrstallise when O2 levels low
  • ->causes sickle shape which gets stuck in small blood vessels
23
Q

Explain the following clinical consequence of the mutation:

accumulation of sickle cells in small blood vessels

A
  • downstream tissue ischaemia- causes pain AND infarction

- inherited & chronic disease with periodic painful heart attacks

24
Q

How does the sickle-cell trait affect the African population and the Africa-American population in the U.S?

A
  • common in Sub-Saharan Africa- sickled red blood cells provide protection against malarial parasites
  • ->gives individual with mutations selective advantage
  • In US malaria not endemic-sickle cell trait slowly disappearing from Africa-American population
25
Q

What may happen if a deletion/ insertion in the DNA sequence occurs?

A
  • could result in significant changes of protein sequence

- ->frameshift mutation

26
Q

Outline the steps taken for protein synthesis (refer to figure 12)

A
  • DNA code transcribed into mRNA in nucleus
  • protein synthesis takes place outside nucleus
  • DNA too big to leave nucleus BUT mRNA small + mobile
  • ->mRNA leaves nucleoplasm via nuclear pore in nuclear envelope & enters cytoplasm
  • ->mRNA then able to travel to ribosomes for translation of DNA code in to proteins
27
Q

What is the composure of ribosomes? (figure 13)

A
  • composed of ribosomal RNA (rRNA) & ribosomal proteins

- consists of 60S subunit AND smaller 40S subunit

28
Q

How may you find ribosomes with the rough ER?

A

-can be free OR attached to the rough endoplasmic reticulum

29
Q

Explain how tRNA molecules work (figure 14)

A
  • tRNA molecules have complementary base triplets which match up to mRNA code
  • there is tRNA for each codon
  • tRNA molecules have amino acids attached
  • matching tRNA & mRNA means amino acids assembled in correct sequence
30
Q

Outline the structure of tRNA molecules (figure 14)

A
  • tRNA bound to amino acid Aminoacyl tRNA (AKA charged tRNA)
  • tRNA molecules which had amino acids removed known as deacylated OR uncharged tRNA
  • tRNA molecule bound to growing polypeptide chain known as peptidyl tRNA
31
Q

Define the term initiation

A

-binding of ribosomes to 5’ end of mRNA AND hydrogen binding of anticodon of aminoacylated tRNA carrying methionine on AUG start codon

32
Q

What is elongation?

A
  • further amino acid addition to growing polypeptide brought corresponding aminoacylated tRNA’s
  • peptidyl transferase creates covalent peptide bonds between amino acids
33
Q

Outline what termination is

A

-when stop codon (UAG, UAA and UGA) reached AND peptide & ribosomal subunits released

34
Q

What happens in translation? (refer to figure 15)

A
  • translation process incorporates 20 different amino acids in precise sequence
  • ->dictated by 3-base codons built from 4 bases from alphabet
  • this process in ribosome builds polypeptide chains- which will become proteins
35
Q

Once polypeptide chain has been synthesised what happens to it

A

1-has to acquire secondary structure
–>a-helices AND B-pleated sheets
2-needs to fold into tertiary structure
3-then has to assemble into quaternary structure if appropriate
-proteins have to reach their destination
–>proteins destined for use within cytoplasm synthesised on free ribosomes
–>proteins destined for secretion out of cell synthesised on ribosomes attached to rough ER

36
Q

Describe the rough endoplasmic reticulum (RER)

A
  • system of flattened cavities
  • ->lined by thin membrane running from nuclear envelope AND into cytoplasm & with many ribosomes on it’s surface
  • ->provides compartment for protein synthesis
37
Q

Explain the first stage of the synthesis- the protein on ribosomes attached to ER (figure 16 is a visual representation)

A
  • secreted proteins have special signal sequence- these interact with RER membrane- synthesis on ribosomes
  • proteins incorporated into vesicles for transport to golgi apparatus
  • ->small spherical compartments made from RER membrane
38
Q

Describe the golgi apparatus

A
  • system of flattened plate-like cavities

- ->lined by thin membrane

39
Q

Explain what happens in the second stage of synthesis where modification occurs (figure 17)

A
  • vesicle moves to golgi apparatus (golgi complex)
  • post-translation modification occurs of protein in GA cavities
  • ->like glycosylation of membrane spanning proteins
40
Q

After the modification has happened what happens to the protein (refer to figure 17)

A
  • modified protein transverses golgi apparatus AND is packed in to secretory vesicles
  • protein containing secretory vesicles moves to cell membrane
  • ->fuses with it and expels it’s content into extracellular space (exocytosis)
  • some specialised golgi apparatus vesicles- called lysosomes contain enzyme which able to digest old organelles

BIOLOGY-FY (12 decks)

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