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USMLE Biochemistry > Cell structure > Flashcards

Cell structure Flashcards

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USMLE® Step 1 flashcards
1
Q

Where are membrane bound ribosomes found?

A

RER (rough endoplasmic reticulum)

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2
Q

What type of proteins do membrane bound ribosomes (on RER) produce?

A

Proteins that are mostly secreted from cell
- Protein hormones, digestive enzymes

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3
Q

What type of proteins do free ribosomes (cytosol) produce?

A

Proteins mostly used by cell
- Metbolism, structure

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4
Q

What are Nissl bodies?

A

RER in neurons
- Synthesize NTs

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5
Q

RERs are abundant in what type of cells?

A

Secretory cells
- Goblet cells (mucus)
- Plasma cells (antibodies)
- Pancreatic Beta cells (insulin)

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6
Q

What is the function of the golgi?

A

Modifies and transports proteins
- Proteins sorted/shipped by adding signal sequences

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7
Q

What is the functions of the smooth endoplasmic reticulum?

A
  • Lipid/steroid synthesis
  • Detoxification of drugs and toxins
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8
Q

Why is the smooth endoplasmic reticulum called ‘smooth’?

A

It is part of the endoplasmic reticulum w/o ribosomes

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9
Q

What does the sarcoplasmic reticulum contain?

A

Calcium

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10
Q

What is the smooth endoplastic reticulum known as in myocytes?

A

Sarcoplastic reticulum

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11
Q

What tissues have lots of SER?

A
  • Hepatocytes (cholesterol synthesis, detoxification, CYP450)
  • Adrenal glands
  • Gonads
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12
Q

What face of the golgi do vesicles from the RER enter into?

A

Cis face (cis golgi network)

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13
Q

Where do vesicles leave the golgi from?

A

Trans face

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14
Q

What is an oligosaccharide?

A

Polymer (chain) of sugar molecules

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15
Q

How can the golgi modify oligosaccharides?

A
  • Attach a Nitrogen (asparagine)
  • Attach an Oxygen (serine/threonine)
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16
Q

What amino acids commonly have a sugar added in the golgi?

A

Serine/threonine (extra O molecule)

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17
Q

What molecule can be added to proteins destined for lysosomes?

A

Mannose-6-phosphate
- Triggers packaging in trans-golgi to lysososmes

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18
Q

What molecules have mannose-6-phosphate added to them to be taken to lysosomes?

A

N-linked oligosaccharides

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19
Q

What disease has an abnormal or disrupted processing in golgi where mannose-6-phosphate is not found on lysosomes?

A

I-cell disease

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20
Q

How is I-cell disease inherited?

A

AR

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21
Q

What are the clinical features of I-cell disease?

A

Onset in 1st year of life
- Growth failure
- Coarse facial features
- Hypotonia/ motor delay

22
Q

What type of disease is I-cell (inclusion cell) disease?

A

Lysosomal stroage disease (mucolipidosis)

23
Q

What enzyme is deficient in I-cell disease?

A

N-acetylglucosaminyl-1-phsophotransferase

24
Q

What is the function of N-acetylglucosaminyl-1-phsophotransferase (deficient in I-cell disease)?

A

Adds phosphate to mannose

25
Q

What enzymes are missing from the lysosomes yet can be found in the blood/urine in I-cell disease?

A

Hydrolases

26
Q

What will the lysosomes contain in I-cell disease?

A

Inclusions of glycosaminoglycans and glycolipids

27
Q

How are endosomes formed?

A

Endocytosis
- Invagination of plasma membrane to surround molecules
- Pinching of membrane to form an enclosed structure

28
Q

What are the different types of endocytosis?

A
  • Receptor mediated (cells take up specific molecules, ligands, that bind receptors)
  • Pinocytosis (droplets)
  • Phagocytosis
29
Q

What type of enzymes are contained inside lysosomes?

A

Acid hydrolase enzymes

30
Q

What is the pH roughly inside a lysosome?

A

~ 4.8

31
Q

How many enzymes are thought to make up lysosomes? (acid hydrolase enzymes)

A

40+

32
Q

What are perioxisomes?

A

Cellular organelles which contain oxidative enzymes (e.g. hydrogen peroxide)

33
Q

What does catalse do?

A

Oxidizes substances with H2O2
- Detoxifies many sunstances in liver cells
- Can metabolize ethanol (alternative, minor pathway)

34
Q

How can perioxisomes affect fatty acids?

A

Beta oxidation of fatty acids
- Preferentially oxidize longer fatty acids

35
Q

Where other than the perioxisomes can beta oxidation occur?

A

Mitochondria (majority)

36
Q

What is the function of proteosomes?

A

Destroy aberrant proteins (misshaped/misfolded)
- Req

37
Q

What is the structure of proteasomes?

A

Barrel-shaped structure
- Protein complex which requires multiple protein subunits

38
Q

What do proteasomes require to function?

A

ATP

39
Q

What are proteins usually marked with before being destroyed by proteasomes?

A

Ubiquitin

40
Q

What neurological disease is thought to have an association with reduced ubiquitin-proteasome activity?

A

Parkinson’s disease
- Toxic accumulation of proteins in neurons

41
Q

What pulls free ribosomes to ER membrane?

A

Signal sequences
- Creates RER

42
Q

Where are signal sequences found?

A

Proteins undergoing synthesis (translation)
- Short peptides
- Found on N-terminal of protein

43
Q

What are signal sequences recognized by?

A

Signal recognition particle (SRPs)
- Found in cytosol

44
Q

What is the function of Signal recognition particle (SRPs)?

A

Move proteins from cytosol to ER lumen

45
Q

What does the SRP bind to and where?

A

SRP receptor on ER membrane

46
Q

What are 3 well-characterized coats found on the surface of vesicles?

A
  • Clathrin
  • COPI
  • COPII
47
Q

What are clathrin-coated vesicles found?

A
  • Transport between plasma membrane and golgi
  • Also to/from endosomes in cytoplasm
  • Extraceullar uptake (endocytosis)
48
Q

What recpetors contain clathrin-coated pits?

A
  • LDL-receptor
  • GF receptor
49
Q

What type of vesicle coats carry things from the golgi to ER (retrograde)?

A

COPI

50
Q

What type of vesicle coats carry things from the ER to the golgi (anterograde)?

A

COPII

USMLE Biochemistry (44 decks)

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