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USMLE > BIOCHEM > Flashcards

BIOCHEM Flashcards

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USMLE® Step 1 flashcards
1
Q

Most abundant protein in the human body.

A

Collagen

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2
Q

Collagen general function

A

Organizes and strengthens extracellular matrix.

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3
Q

Collagen synthesis and structure

steps inside fibroblasts and where inside of them

A
  1. Synthesis (RER)
  2. Hydroxylation (ER)
  3. Glycosylation (Golgi)
  4. Exocytosis
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4
Q

Collagen synthesis and structure steps outside fibroblasts

A
  1. Proteolytic processing 6. Cross-linking
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5
Q

Collagen synthesis and structure Synthesis (RER)

A

Translation of collagen α chains
(preprocollagen)— usually Gly-X-Y polypeptide (X and Y are
proline, hydroxyproline, or hydroxylysine).

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6
Q

Collagen synthesis and structure

Hydroxylation (ER)

A

Hydroxylation of specific proline and lysine

residues (requires vitamin C).

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7
Q

Collagen synthesis and structure

Glycosylation of pro-α-chain lysine residues and formation of procollagen (triple helix of three collagen α chains).

A

Glycosylation (Golgi)

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8
Q

Collagen synthesis and structure
Exocytosis of procollagen into extracellular
space.

A
  1. Exocytosis
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9
Q

Collagen synthesis and structure

Cleavage of terminal regions of procollagen transforms it into insoluble tropocollagen.

A
  1. Proteolytic processing
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10
Q

Collagen synthesis and structure
Reinforcement of many staggered tropocollagen molecules by covalent lysine- hydroxylysine cross-linkage (by lysyl oxidase) to make col- lagen fibrils.

A
  1. Cross-linking
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11
Q

Chédiak-Higashi syndrome mech

A

is due to a microtubule polymerization defect resulting in ↓ phagocytosis

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12
Q

Molecular motors
Dynein =
Kinesin =

A

Molecular motors
Dynein = retrograde.
Kinesin = anterograde.

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13
Q

Drugs that act on microtubules:

A
  1. Mebendazole/thiabendazole (antihelminthic)
  2. Taxol (anti–breast cancer) 3. Griseofulvin (antifungal) 4. Vincristine/vinblastine (anti-cancer)
  3. Colchicine (anti-gout)
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14
Q

Vesicular trafficking proteins:

trans-Golgi → lysosomes, plasma membrane → endosomes (receptor-mediated endocytosis).

A

Clathrin

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15
Q

I-cell disease clinical findings

A

Characterized by coarse facial features, clouded corneas, restricted joint movement, and high plasma levels of lysosomal enzymes. Often fatal in childhood.

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16
Q

I-cell disease mech

A

failure of addition of mannose-6- phosphate to lysosome proteins, enzymes are secreted outside the cell instead of being targeted to the lysosome.

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17
Q

what cells are particularly rich in SER.

A

Liver hepatocytes and steroid hormone–producing cells of the adrenal cortex

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18
Q

Osteogenesis imperfecta 4 findings

A
  1. Multiple fractures
  2. Blue sclerae
  3. Hearing loss (abnormal middle ear bones)
  4. Dental imperfections due to lack of dentition
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19
Q

Osteogenesis imperfecta worst type and findings

A

Type II is fatal in utero or in the neonatal period.

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20
Q

5 Immunohistochemical stains and associated cell types

A 
Vimentin - Connective tissue
Desmin - Muscle
Cytokeratin - Epithelial cells
Glial fibrillary acid proteins (GFAP) - Neuroglia
Neurofilaments - Neurons
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21
Q

Stretchy protein within lungs, large arteries, elastic ligaments.

A

Elastin

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22
Q

Elhers-Danlos syndrome mech and clinical findings

A

Faulty collagen synthesis (Type III is most frequently affected (resulting in blood vessel instability) causing:

  1. Hyperextensible skin
  2. Tendency to bleed (easy bruising)
  3. Hypermobile joints 4.Associated with berry aneurysms.
23
Q

Collagen Types Type I

A

(90%)––Bone, Skin, Tendon, dentin, fascia, cornea, late wound repair.

24
Q

Collagen Types Type II

A

Cartilage (including hyaline), vitreous body, nucleus pulposus.
Type II: carTWOlage.

25
Q

Collagen Types Type III (Reticulin)

A

skin, blood vessels, uterus, fetal tissue, granulation tissue.

26
Q

Collagen Types Type IV

A

Basement membrane or basal lamina.

Type IV: Under the floor (basement membrane)

27
Q

Cilia structure

A

9 + + 2 arrangement of microtubules.
Dynein is an ATPase that links peripheral
9 doublets and causes bending of cilium by
differential sliding of doublets.

28
Q

Microtubule structure

A

Cylindrical structure 24 nm in diameter and of variable length. A helical array of polymerized dimers of α- and β-tubulin (13 per circumference). Each dimer has 2 GTP bound.

29
Q

Microtubule functions

A

has 2 GTP bound. Incorporated into flagella, cilia,

mitotic spindles.Microtubules are also involved in slow axoplasmic transport in neurons.

30
Q

Vesicular trafficking proteins:

Anterograde, RER → cis-Golgi.

A

COP II

31
Q

Vesicular trafficking proteins: Retrograde,

Golgi → ER.

A

COP I

32
Q

6 Functions of Golgi apparatus

A
  1. Distribution center of proteins and lipids from
    ER to the plasma membrane, lysosomes, and secretory vesicles
  2. Modifies N-oligosaccharides 3. Adds O-oligosaccharides 4. Addition of mannose-6- phosphate
  3. Proteoglycan assembly
  4. Sulfation
33
Q

α1-antitrypsin inhibits

A

elastase

34
Q

Elastin structure

A

Rich in proline and lysine, nonhydroxylated forms.

35
Q

Fetal alcohol syndrome worst window

A

3–8 weeks

36
Q

Plasma membrane wrt cholesterol

A

High cholesterol or long saturated fatty acid content → increased melting temperature and decreased fluidity.

37
Q

Kartagener’s syndrome mech and clinical findings

A

Immotile cilia due to a dynein arm defect. Results in male and female infertility (sperm immotile), bronchiectasis, and recurrent sinusitis (bacteria and particles not
pushed out); associated with situs inversus.

38
Q

what cells are particularly rich in RER.

A

Mucus-secreting goblet cells of the small intestine and antibody-secreting plasma cells

39
Q

SER is the site of

A

steroid synthesis and detoxification

of drugs and poisons.

40
Q

RER is the site of

A

synthesis of secretory (exported) proteins and of N-linked oligosaccharide addition
to many proteins.

41
Q

Checkpoints control transitions between phases. Regulated by

A

cyclins, cdks, and tumor suppressors.

42
Q

Cell cycle phases

Labile cells what and examples

A

Never go to G0, divide rapidly with a short G1.

Bone marrow, gut epithelium, skin, hair follicles.

43
Q

Cell cycle phases Stable cells what and examples

A

Enter G1 from G0 when stimulated.

Hepatocytes, lymphocytes.

44
Q

Cell cycle phases

Permanent cells what and examples

A

Remain in G0, regenerate from stem cells.

Never go to G0, divide rapidly with a short G1.

45
Q

Cell cycle phases shortest phase

A

Mitosis

46
Q

Posttranslational modifications Proteasomal degradation

A

Attachment of ubiquitin to defective proteins to tag them for breakdown.

47
Q

Posttranslational modifications Covalent alterations

A

Phosphorylation, glycosylation, and hydroxylation.

48
Q

Plasma membrane composition with %’s

A

Asymmetric fluid bilayer. Contains cholesterol (~50%), phospholipids (~50%), sphingolipids, glycolipids, and proteins.

49
Q

Ouabain mech

A

inhibits Na+-K+ATPase by binding to K+ site.

50
Q

Na+-K+ATPase location and orientation

A

Na+-K+ATPase is located in the plasma membrane

with ATP site on cytoplasmic side. For each ATP consumed, 3 Na+ go out and 2 K+ come in.

51
Q

Elastin what and where

A

Stretchy protein within lungs, large arteries, elastic ligaments.

52
Q

Marfan’s syndrome is caused by a defect in?

A

fibrillin.

53
Q

Elastin wrt diseases

A

Emphysema can be caused by excess elastase activity

USMLE (7 decks)

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