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BIOSCI 107 > L8 - Gene To Protein > Flashcards

L8 - Gene To Protein Flashcards

1
Q

Genotype

A

Organism’s hereditary info

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2
Q

Phenotype

A

Actual observable/physiological traits

= genotype + interaction w/environ.

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3
Q

Control points of gene expression

A
  • transcription
  • processing of pre-mRNA
  • transport
  • translation
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4
Q

Importance of control points

A

Gene expression tightly regulated to achieve right thing at right time in the right place (temporal/spatial control)

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5
Q

DNA orientation

A

Upstream = promotor end = 3’ end of template strand = 5’ end of non-template strand
- has control elements that dictate things need to be assembled: when and how

Downstream = terminator end = 5’ end of template strand = 3’ end of non-template strand

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6
Q

Purines

A

Adenine, guanine

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7
Q

Pyrimidine

A

Thymine, cytosine

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8
Q

Transcription initiation

A

1) eukaryotic promotor (TATA box sequence ~25 nt upstream)
2) promotor assemble transcription factors (including TATA box binding protein, TBP) - allows RNA polymerase II to bind
3) transcription factors + RNA polymerase II (teardrop shaped enzyme) form transcription initiation complex

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9
Q

Transcription elongation

A

10-20 nucleotides exposed at a time when DNA unwound (H-bonds broken)

  • H-bonds between RNA nucleotides and DNA bases
  • phosphodiester bonds between RNA nucleotides
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10
Q

Transcription termination

A

1) polyadenylation signal (AAUAAAA)

2) pre-mRNA released, RNA polymerase dissociated

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11
Q

Fidelity (proofreading)

A

Less than for DNA replication

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12
Q

UTR

A

Untranslated regions at 5’ and 3’ ends

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13
Q

Steps of processing pre-mRNA transcript

A

Capping, tailing, splicing

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14
Q

Capping

A

Modified guanine added to 5’ end

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15
Q

Tailing

A

50-250 adenine nucleotides (polyA) added (strand is polyadenylated) to 3’ end to form poly-A-tail

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16
Q

Splicing location

A

Spliceosome

  • large complex of proteins and small RNA
  • in nucleus
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17
Q

Alternative splicing

A
  • process by which different combos of exons are joined together
  • results in production of multiple forms of mRNA from single pre-mRNA
  • 1 gene to multiple gene products
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18
Q

Translation components

A

Ribosomes, tRNA

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19
Q

Ribosome sites

A
  • mRNA binding site on small subunit

- tRNA binding sites on large subunit

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20
Q

tRNA binding sites

A
  • A (aminoacyl-tRNA binding) site: holds next-in-line tRNA
  • P (peptides-tRNA binding) site: holds tRNA carrying the growing polypeptide
  • E (exit) site: tRNAs exit from here
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21
Q

Translation process

A
  • codons translated into amino acids

- protein synthesis catalysed by ribosomes

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22
Q

Initiator tRNA

A

TRNA carrying methionine (Met)

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23
Q

Translation initiation

A

1) small ribosomal subunit with initiator tRNA + bind to 5’ cap end of mRNA
2) small ribosomal subunit scans downstream to find translation start site (AUG)
3) H-bond between anticodon/mRNA
4) large ribosomal subunit binds = initiation complex
GTP required

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24
Q

GTP

A

Guanosine triphosphate

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25
Q

Translation elongation

A

1) codon recognition
- tRNA in cytosol + complementary codon
- GTP invested to increase accuracy/efficiency
2) peptide bond formation
- large subunit rRNA catalyses peptide bond
- polypeptide moves from P site tRNA to A site tRNA
3) translocation
- P site tRNA moves to E site then released
- A site tRNA moves to P site
- GTP required

26
Q

Empty tRNA reloading

A

In cytoplasm using aminoacyl-tRNA synthetases (family of related enzymes e.g tyrosyl-tRNA synthetase)

27
Q

Amino acid-tRNA bond

A

Covalent

28
Q

Translation termination

A

1) stop codon
2) release factor to A site
3) release factor promotes hydrolysis of bond between P site tRNA and last amino acid
4) polypeptide released
5) ribosomal subunits + other components dissociate and recycled
- hydrolysis of TWO GTP molecules required

29
Q

Nascent

A

Growing (e.g polypeptide)

30
Q

Polypeptide orientation

A 
N terminus (amino end) = 5’ end of mRNA
C-terminus (carboxyl end) = 3’ end of mRNA
31
Q

R group of amino acid

A

Side chains determine property of each amino acid and therefore final structure and function of protein

  • nonpolar = hydrophobic
  • polar= hydrophilic
  • electrically charged = hydrophilic (acidic-negatively charged, basic-positively charged)
32
Q

No. Amino acids

A

Twenty standard (coded for) amino acids

33
Q

Protein structures

A

Primary, secondary, tertiary, quarternary

- all proteins go to tertiary

34
Q

Primary structure

A
  • determined by sequence
  • held by covalent bonds
  • starts to form secondary structures as soon as it leaves ribosome (Protein assumes 3D conformation either spontaneously as it emerges from ribosome or with help of chaperones)
35
Q

Chaperones

A

Proteins that assist with protein folding

one type provides the right conditions for folding e.g pH, conc. etc.

36
Q

Secondary structure

A
  • can be predicted by sequence
  • held by weak H-bonds
  • alpha helix or beta pleated sheets
37
Q

Tertiary structure

A
  • less predictable

- 3D shape stabilised by side chain interactions

38
Q

Quarternary structure

A

Multiple proteins associate together to form functional protein
E.g hemoglobin

39
Q

Functional classification of proteins

A

Housekeeping proteins, other proteins

40
Q

Housekeeping proteins

A

continuously produced

  • commonly used
  • protein/mRNA present in large quantities
  • (typically) longer half-life in cells
41
Q

Other proteins

A

Produced in response to stimuli as required

  • cell signalling
  • signal transducted and many enter nucleus to activate transcription
  • results in production of short-lived protein to carry out required function
42
Q

Translation location

A

All commence on free ribosomes

1) cytosolic proteins - complete on free ribosomes
2) proteins going through endomembrane system (RER and Golgi) - complete translation at fixed ribosomes on RER (target specific receptors)

43
Q

Signal peptides

A

Located at N terminus of protein (~20 amino acids) and are what direct ribosomes to RER

44
Q

SRP

A

Signal recognition particle

45
Q

Signalling process

A

1) polypeptide synthesis begins
2) SRP binds to signal peptide which pauses translation
3) SRP binds to receptor protein on RER
4) SRP detaches and polypeptide synthesis resumes
5) signal sequence inserts into ER membrane and nascent chain is translocated across
6) signal peptidase (signal-cleaving enzyme) cuts off signal peptide
7) completed polypeptide folds into final conformation

46
Q

Secretory proteins

A

Solubilised in ER lumen

E.g insulin

47
Q

Membrane protein

A
  • Remains anchored to membrane (one or more hydrophobic segments of polypeptide anchor it in the bilayer)
  • vesicle forms around it
48
Q

Vesicles go to

A

Golgi for further maturation then to plasma membrane where they are

  • secreted
  • remain at cell surface
  • targeted to lysosomes where they serve degradation of nutrients and facilitate renewal of the cell’s own macromolecules
49
Q

Post-translational modifications

A 
Confer activity
- phosphorylation
- cleavage
Ability to interact with other molecules
- methylation
- biotinylation
Direct to particular locations
- ubiquitination
Other
- acetylation
- carboxylation
- carbohydrate addition
50
Q

Post-translation modification location

A
  • some in golgi

- others in cytosol

51
Q

Gene examples

A
  • TATA-box binding protein (TBP)

- Huntington (HTT)

52
Q

Genome

A

All DNA as a whole
~3000 Mbp
~20,000 genes

53
Q

if translation terminated at wrong place for cytosolic/proteins going through endomembrane system

A

proteins won’t fold correctly (wrong conditions) = non-functional protein

54
Q

secretory and membrane proteins terminate translation

A

on rough ER

55
Q

sorting error

A

protein correct but in wrong place

- may have fully folded and modified protein but trafficked incorrectly so can’t do its job

56
Q

failure of post-translational modifications

A

non functional protein

57
Q

poor proofreading

A

transcript present but may or may not function as a protein depending on effect on amino acid

58
Q

failure of splicing

A

introns not removed = have a pre-mRNA but correct protein won’t be made

59
Q

absence of RNApol II or other required factor

A

no transcription = no transcript at all

60
Q

incorrect folding of protein

A

non-functional protein

61
Q

effect of errors

A

if only a small proportion of products affected, may not be catastrophic

BIOSCI 107 (15 decks)

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