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MCB 450 > Class 3: Digestion, Turning a Meal into Cellular Biochemicals > Flashcards

Class 3: Digestion, Turning a Meal into Cellular Biochemicals Flashcards

1
Q

What is eliminated when the monomeric units in proteins, carbohydrates, and nucleic acids are joined

A

H2O is eliminated

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2
Q

What is the property of hydrolyses

A

they cleave their substances by the addition of a water molecule

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3
Q

Protein digestion steps

A
  • Begin in stomach by hydrochloric acids and pepsin
  • Protein-digesting enzymes are secreted from the pancreas into the small intestine
  • small intestine is major site of protein digestion
  • small amount lost in feces
  • final digestion of dipeptides and tripeptides to amino acids also occurs in the intestine
  • absorbed amino acids enter the blood and travel to the liver
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4
Q

Which organ regulates distribution of amino acids to the rest of the body

A

Liver

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5
Q

slide 5

A

answer

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6
Q

what r the rose of hydrochloric acid(gastric acids) in food digestion

A

1) protein denaturation
- acids and bases disrupt ionic bonds and prevent hydrogen bonding

2) Stomach: pepsinogen is activated by HCL and pepsin

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7
Q

What r the 3 steps for the secretion and activation of proteases

A

1) stomach: pepsin activated by HCL
- dietary protein + pepsin = polypeptides and amino acids

2) small intestine: pancreatic enzymes are activated by eterokinase(eneropeptidase) and proteases

3) Activation of Proteases
- proenzymes(zymogens) —> active enzymes

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8
Q

slide 8

A

answer

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9
Q

Steps of transport of amino acids into cells

A

1) from intestinal lumen into epithelial cells
- Na+ dependent transport

2) From epithelial cells into the blood
- the amino acid is carried by facilitated transporter down to its concentration gradient into the blood

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10
Q

Which two types of cells and where have a common/similiar transporter system for amino acids uptake

A

epithelial cells in small intestine
and renal tubular epithelial cells in kidney

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11
Q

Amino acid Transporter System 1
neutral amino acids

A

AA transported: Ala, Gly, Ser, Thr, Val, Leu, Ile, Phe, Tyr, Trp, Asp, His, Cys, Met, citulline

Inherited Disorder: Hartnup disease

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12
Q

amino acid transporter 2
dibasic amino acids

A

AA Transported: Lys, Arg, ornithine, cystine

Inherited disorder: Cystinuria or dibasic aciduria

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13
Q

AA Transporter Systems 3
dicarboxylic amino acids

A

AA transported: Glu, Asp

Inherited disorders: Dicarboxylic acidur

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14
Q

AA Transporter System 4
glycine and amino acids

A

AA transported: Fly, Pro, Hydroxyproline

Inherited disorder: joespehs syndrome or glycinuria

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15
Q

What is Neutral amino acuduria: Hartnup disease

A

-genetic defect in transporter genes: SL6A19(absorbs neutral polar amino acids)

-loss of amino acids in body particularly tryptophan

-triptophan can be converted to serotonin(neurotransmitter) melatonin(neurohormone) and niacin(B3)

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16
Q

What are the symptoms of hartnup disease

A

dermatitis , dementia, and diarrhea

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17
Q

What is Cystinuria

A

-is an aminoaciduria in which large amounts of cystine is found in urine.
- disorder of the proximal tubules reabsorption of filtered cystine
- this leads to accumulation and subsequent precipitation of stones of cystine in the urinary tract
- Most common genetic error of amino acid transporter: in 7,000

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18
Q

what is the difference between cysteine and cystine

A

cystine has two S molecules connect with each other by disulfide bonds

cysteine does not have this connection, the S for sulfyhydrl groups or two S-H

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19
Q

What is a monosaccharide

A

single polyhydroxy alcohol or ketone unit, cyclized,
(e.g. 6-carbon glucose, most abundant in nature)

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20
Q

what is an oligosaccharide

A

short chain of 2- ~20 monosaccharides joined by “glycosidic bonds”
(e.g. disaccharide sucrose = glucose-fructose)
- oligosaccharides > 3 residues are often joined to protein or lipid in “glycoconjugates

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21
Q

what is a polysaccharide

A

chains > ~ 20 to 1000s of monosaccharides in length
- linear: e.g. cellulose (glucose)n
- branched: e.g. glycogen & starch (glucose)n
-depending on the sugar residues in a polysaccharide & the linkages between them, polysaccharides can have very different biological roles

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22
Q

what is a polysaccharide

A

chains > ~ 20 to 1000s of monosaccharides in length
- linear: e.g. cellulose (glucose)n
- branched: e.g. glycogen & starch (glucose)n
-depending on the sugar residues in a polysaccharide & the linkages between them, polysaccharides can have very different biological roles

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23
Q

what are the sites of breakdowns for carbohydrates

A

1) mouth
- digestion of carbohydrates starts from the mouth by salivary @-amylase…this breaks down @-1,4-Glycosidic bond

2) small intestine

24
Q

what breaks down Maltose

A

maltase —> glucose

25
Q

what breaks down lactose

A

lactase —> glucose + galactose

26
Q

what breaks down sucrose

A

sucrase —> glucose + fructose

27
Q

What is the difference between @-glucos and B-glucose

A

@ - the hydroxyl group attached to C-1 and the -CH2OH group at C-5 lies on opposite sides of the ring’s plane

B - the same side of the plane

28
Q

What causes lactose intolerance?

A

reduced levels of lactase due to silencing of the lactase gene

29
Q

3 treatments for lactose intolerance

A

1) reduce consumption of milk
2)use lactase-treated products
3)take lactase in pill prior to eating

30
Q

What r fatty acids used for

A

most commonly used as fuel

31
Q

triacylglycerols

A

storage form of fatty acids

32
Q

phospholipids

A

membrane lipids

33
Q

glycolipids

A

bound to carbohydrates membrane compnents

34
Q

steroids

A

they are polycyclic hydrocarbons, signaling molecule and mean components

35
Q

what r the sites of lipid digestion

A

stomach and mouth

36
Q

what are the enzymes for lipid digestion in the stomach

A

-mouth: lingual lipase
-stomach: gastric lipase

37
Q

what r the enzymes for lipid digestion found in the liver(pancreatic enzymes) ?

A

Lipase and co-lipase
Cholesterol esterase
Phospholipase A2
Lysophospholipase

38
Q

how does lipid digestion occur in the stomach

A
  • acid stable and remove short and medium chains (< 12 C) fatty acids from TAGS
  • most active in infants and young children who drink cows milk
  • emulsion occurs in the stomach
39
Q

slide 25

A

answer

40
Q

what does cholecystokinin do

A
  • is produced in the presence of lipids and partially digested protein

1) acts on stomach to slow gastric motility
2) acts on gall bladder to contract and release pancreatic lipase
3) acts on pancreas to release pancreatic lipase

41
Q

what does secretin do

A
  • produced by intestinal endocrine cells in response to the low pH of the chyme entering the duodenum from the stomach

cause the pancreas and liver to release bicarbonate to neutralize the pH of intestinal contents (pH 5-6)

42
Q

what is emulsification

A

it increases the surface area of the hydrophobic lipid droplets so the digestive enzymes can act effectively

43
Q

what r the two complementary mechanisms through which emulsification is accomplished

A
  • use of detergent properties of the bile salts (amphipathic)
  • mechanical mixing due to wave-like movement of the intestine
44
Q

Are unconjugated or conjugated bile salts soluble in water

A

conjugated bile salts r soluble in water

45
Q

what r bile salts

A
  • derivatives of cholesterol
  • consist of a sterol ring structure with a side chain to which a molecule of glycine or taurine is covalently attached by an amide linkage
46
Q

absorption of lipids in form of micelles

A

1) tiny mickrodroplets that emulsified by bile salts, solubilizing lipid
2) Micelles contain majority fatty acids and 2-monoacylglycerols.
3) Disc-shaped clusters of amphipathic lipids. Arranged with their hydrophobic groups on the inside and their hydrophilic groups on the outside
4) The micelles travel through a layer of water to the microvilli on the surface of the intestinal epithelial cells, where the fatty acids, 2-monoacylglycerols, and other dietary lipids are absorbed, but the bile salts are left behind in the lumen of the gut.
5) Short- and medium-chain fatty acids (C4 to C12) do not require bile salts for their absorption.

47
Q

what r the 4 steps of re-sysnthesis of lipids by intestinal mucosal cells

A

1) Activation of long chain fatty acids into acyl CoA

2) synthesis of TG from monoacylgylcerol

3) synthesis of cholesterol ester from cholesterol

4) synthesis of phospholipids from glycerolphosphoryl base

48
Q

Newly synthesized TG and cholesterol ester are packaged as lipid droplets surrounded by thin layer of: ??

A

Apolipoprotein B-48 (apo B-48)
Phospholipids
Free cholesterol

49
Q

Secretion of chylomicrons:

A

By exocytosis into lymphatic vessels around villi of small intestine then enter systemic circulation

50
Q

ApoCII

A

is necessary for the activation of lipoprotein lipase, the enzyme that degrades the triacylglycerol contained in the chylomicron.

  • recognized by hepatic receptors
51
Q

“nascent” chylomicron

A

The particle released by the intestinal mucosal cell

  • because it is functionally incomplete. ApoB is the primary organizing protein.
52
Q

5 steps in metabolism of chylomicrons

A

1) intestinal mucosal cells secrete nascent TG- rich chylomicrons produced primarily fro dietary lipids

2)Apo C-II and Apo E are transferred from HDL to the nascent CM

3)extracellular lipoprotein lipase, activated by app c-II degrades TG in CM

4)Apo C-II is retuned to HDL

5) CM remnants bind to specific receptors on the liver where they are endocytosed

53
Q

Steatorrhea

A

the presence of excesss fat in fees due to poor digestion and malabsorption

54
Q

Poor digestion

A

1) a mechanical block in the biliary tract or by intrahepatic

2) chronic pancreatitis, Cystic Fibrosis: mutations in the CFTR (chloride channel on the epithelium) cause decreased hydration and thickened secretions and the pancreatic enzymes are unable to reach the intestine

55
Q

Malabsorption

A

IBD: inflammatory bowl disease causing decreased absorption

56
Q

Steps in the digestion of nucleic acids

A

1) denature of FNA and RNA in the Stomach

2) DNA and RNA into oliigonucleotides by Ribonucleotides and deoxyriboncleotides (pancreatic enzymes)

3) Oligonucleotides into mononucleotides by phosphodiesterase (pancreatic enzymes)

4) In the intestinal mucosal cells, nucleotides removes the phosphate groups, releasing nucleosides

5) nucleosides into pyrimidine and purine by nucleosides

6) Purine is degraded into uric acid and excreted in urine. Pyrimidines enter the circulation and can be reused

MCB 450 (11 decks)

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