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Molecules, Genes, and Disease > Lecture 6 > Flashcards

Lecture 6 Flashcards

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Organic Chemistry 101 flashcards
1
Q

Ribosomes remain cytosolic if the protein is…

A

destined for the cytosol or posttranslational import into organelles

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2
Q

ribosomes attach to ER membrane if protein…

A

destined for membrane or secretory pathway via co translational insertion

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2
Q

What is required for protein sorting?

A

a signal intrinsic to the protein

a receptor that recognizes the signal and which directs it to the correct membrane

a translocation machinery

energy transfer the protein to the new location

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3
Q

protein import into the mitochondrial matrix

A

1.protein with signal kept unfolded by chaperones

2.signal binds receptor

3.protein fed through channel in adjacent inner membrane

4/ targeting signal cleave

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4
Q

what is Pyruvate dehydrogenase deficiency

A

a mutation at codon 10 in N-MTS of PDH E1a subunit results in Arg to Pro substitution

Reduced uptake into mitochondria

X linked dominant disorder

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5
Q

The classic nuclear import cycle

A
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6
Q

Example of a mutation of the nuclear localisation signals

A

Swyer Syndrome

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7
Q
A
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8
Q
A
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9
Q

What is Swyer Syndrome?

A

loss or mutation of NLS determining SRY protein

XY genotype
outwardly female

SRY required for testis differentiation

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9
Q

Functions of the ER

A

insertion of proteins into membranes

specific proteolytic cleavage

glycosylation

formation of S bonds

proper folding of proteins

assembly of multiunit proteins

hydroxylation of selected Lys and Pro residues

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9
Q

What is Glycosylation

A

most common posttranslational modification

most of the secreted proteins become glycosylated

occurs in ER

further sugar modification takes place in the ER and golgi

Oligosaccharide preassembled on lipid
(dolichol) carrier

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9
Q

N linked Glycosylation -

A

sugars are added on an asparagine side chain (involves an amino group hence N linked)

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10
Q

O linked glycoslyation

A

sugar moiety added to serine or threonine

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11
Q

Why is glycosylation of proteins so important?

A

correct protein folding

protein stability

facilitates interactions with other molecules

deficiencies in N linked glycosylation lead to severe inherited human disease: congenital disorders of glycoslation

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12
Q

Delivery of lysosomal enzymes to the lysosome requires what kind of signal

A

mannose 6 phosphate signal

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13
Q

What enzymes are required in the delivery of lysosomal enzymes to the lysosome

A

N-acetyl glucosamine phosphotransferase and phosphodiesterase

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14
Q

As a lysosomal enzyme passes through the Golgi apparatus…

A

a phosphate group is added to the hydroxyl group of carbon 6
of a mannose sugar

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15
Q

O-linked glycoslation details:

A

occurs in Golgi

attachment of sugar to hydroxyl group of serine, threonine

important in proteoglycans

component of extracellular matrix and mucus secretions

16
Q

Disulphide bond formation

A

occurs in the ER

between 2 cysteine amino acids

Redox reaction with a protein disulphide isomerase (PDI - an ER protein)

C-terminal KDEL motif - signal to return them to the ER
(KDEL = retrieval pathway)

17
Q

how do proteins normally fold and what proteins can assist them?

A

many proteins fold into correct conformation but some need chaperone proteins to help them

18
Q

What 3 things can happen when there are protein folding problems?

A

Protein may be trapped in mis-folded conformation

Protein contains mutation resulting in mis-folding

Protein may be incorrectly associated with other sub-units

18
Q

BiP (chaperone protein)

A

binding immunoglobin protein

19
Q

What does BiP do?

A

binds to exposed amino acid sequences that would normally be buried in the
interior of a folded protein

20
Q

Calnexin and Calreticulin (chaperone proteins)

A

binds to oligosaccharides on incompletely folded proteins

20
Q

how do chaperone proteins act as sensors to monitor extent of protein misfolding?

A

mediate increased transcription of chaperones

mediate reduction in translation

21
Q

what happens if mis folding can not be corrected?

A

protein may return to cytosol for degradation (proteosome)

protein may accumulate to toxic levels in the ER resulting in disease

22
Q

2 examples of post translational modification within the secretory pathway:

A

collagen (constitutive secretion)

insulin (regualted secretion)

23
Q

constitutive secretory pathway meaning

A
  • Cells continuously secrete certain molecules regardless of external signals or stimuli
    • Secretory vesicles that contain the molecules to be secreted bud off from the Golgi apparatus and are transported directly to the cell membrane
    • Once they reach the cell membrane, these vesicles fuse with the cell membrane and release for basic cellular functions or maintaining cellular homeostasis
    • The pathway is involved in the section of molecules that are required for basic cellular functions or maintain cellular homeostasis.
24
Q

Example of constitutive secretion

A

collagen

25
Q

Example of regulated secretion

A

insulin

26
Q

Lecture notes about constitutive secretion

A

Produced all the time and released when produced

good for membrane proteins

good for things needed all the time

27
Q

Lecture notes on regulated secretion

A

produced all the time but need signals for release

stored thus until needed:

endocrine cells - secreting hormones

exocrine cells - secreting digestive juices

neurone cells - secreting neurotransmitters

28
Q

Synthesis and modification of collagen
in ER

A

Hydroxylation of selected lysine and prolines by prolyl
hydroxylase

29
Q

scurvy

A

connective tissue defect

Prolyl hydroxylase requires vitamin C and Fe+ ions for activity

allows increased H-bonding to stabilise
triple helix

thus scurvy is caused by weak tropocollagen triple helices.

30
Q

Transport to and modification of collagen in the golgi

A

assembled procollagen transported to golgi in vesicles

glucose is added to galactose

transport to plasma membrane in transport vesicles

procollagen clead to tropocollagen

-> removal of N and C terminal

Procollagen peptidases

31
Q

What enzyme converts procollagen to tropocollagen

A

procollagen peptidases

32
Q

formation of a collagen fiber

A

tropocollagen - covalent linkage between lysines by lysyl oxidase

-> collagen fibril

then aggregation leads to a collagen fiber.

33
Q

Ehlers Danlos Syndrome mutation

A

Mutation in collagen type 1 111 or V or lysyl oxidase deficinecy

34
Q

insulin release - regulated secretion

A

insulin is produced as an inactive precursor called proinsulin

modified via cleavage into an active version within secretory vesicles

an increase in blood glucose, glucose enters the beta islet cells through GLUT 2 Transporter

So intracellular glucose increases causing calcium influx and release form the ER

Then Calcium uptake releases insulin containing vesicles.

35
Q

Disulphide bonds form in the ER and are required for what?

A

The disulphide bonds are required for the biological activity of insulin

36
Q

Where does disulphide bonds form and what is their function in proinsulin?

A

occurs in the ER and specific folding stabilised by disulphide bonds

37
Q

How does proinsulin become insulin with respect to bonding?

A

connecting peptide removed, leaving two chain insulin molecule

reduction irreversibly separates’ the two chains and this occurs post - golgi in clathrin coated secretory vesicles.

38
Q

Why is proteolytic processing so
common in the secretory pathway?

A

Can give rise to very small products (e.g. enkephalins – 5aa) that would be too
short to enter ER via co-translational mechanism

Some secreted proteins e.g. hydrolytic enzymes would be destructive if activated
inside the cell

Multiple bioactive products can be produced from the same polypeptide

39
Q
A

Molecules, Genes, and Disease (9 decks)

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