Biochemistry 1 Flashcards
(86 cards)
1
Q
Functions of carbohydrates
A
-energy source (via oxidation) and energy storage
-structural component
-informational molecule (in cell signalling)
-carbon C supply for synthesis of cell components
2
Q
Simple vs Complex carbohydrates
A
Simple ones: monosaccharides (contain 1 polyhydroxy aldehyde or ketone unit)
Complex:
-dissacharides (contain 2 monosaccharide unites) -oligosaccharides (contains 2-10 monosaccharide units) -polysaccharides (contain long chains of multiple monisaccharide units)
3
Q
Monosaccharides
A
-simple sugars
-most common one is glucose
-formula is (CH2O)n
4
Q
Aldehyde
A
5
Q
A
Amylose (straight glucose chain)
6
Q
A
Amylopectin (branched glucose chain)
7
Q
A
Lactose (galactose + glucose), beta 1,4
8
Q
A
Cellubiose (2 glucose molecules, beta 1,4 glycosidic bonds)
9
Q
A
Sucrose (glucose + fructose), 1 alpha glucose, 1 beta fructose
10
Q
A
Trehalose (2 glucose residues linked through anomeric position to one another)
11
Q
A
Glucose (common sugar in blood)
12
Q
A
Fructose (fruit sugar)
13
Q
A
Galactose (component of milk sugar)
14
Q
Examples of lipids
A
-fatty acids
-triglycerides
-phospholipids
-sphingolipids
15
Q
Functions of lipids
A
-energy storage
-insulation
-water repellant
-membrane structure
-cofactors for enzymes
-signalling molecule
16
Q
Saturated fatty acids
A
-no double bond
17
Q
Unsaturated fatty acids
A
-1 or more double bonds
18
Q
Triacylglyerols TAG
A
-clusters of fatty acids
-formed by condensation reaction
-glycerol bone
-ester bonds O-C=O
-solids= fats, contain only saturated fatty acids
-liquids=oils, contains atleast one unsaturated fatty acid forming oils
19
Q
Glycerophospholipids
A
-glycerol base
-2 fatty acids
-phosphate group
20
Q
Glycerophospholipids
A
-glycerol base
-2 fatty acids
-phosphate group
21
Q
A
Triacylglycerol
22
Q
A
ester bonds
23
Q
Sphingolipids
A
-backbone is sphinosine
-blood groups are determined by the type of sugars located on the head groups
24
Q
Sterols
A
-subgroup of steroids
-amphiphatic lipid
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Cholesterol
-lipid
-essential for cell membrane
-unpolar molecule
-has hormone properties ie. steroid hormones
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Steroid hormones
-synthesized from cholesterols
-carried in the blood stream
ie.
-cortisol
-testosterone
-prednisone
-estradiol
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Waxes
-lipids
-esters with long chain of alcohol
-insoluble
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Biologically active lipids
-D, E, K, erythromycin
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Enzymes
-catalysts
-increase reaction rate
-are globular proteins
-structure ensured by AA sequence
- do not affect equilibrium
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Enzymes enhance rate
-when catalyst is missing, the equilibrium is reached slowly
-when enzyme is present, the speed increases
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Carbonic anhydrase
-enzyme that assists rapid inter-conversion of carbon dioxide and water into carbonic acid, protons and bicarbonate ions
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Enzyme specifity
-work with only 1 substrate (=substrate specificity)
-work with several substrates (=relative substrate specificity)
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Bond specific enzymes
-act on particular type of chemical bond
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Group specific enzyme
-act on molecules that have specific functional group
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Stereospecific enzyme
-acts on particulat steric or optical isomer
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Catalytic mechanisms of enzymes
1. acid base catalysis: give or take protons
2. covalent catalysis: change reaction paths
3. metal ion catalysis: use redox cofactors
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Enzyme types (classifications)
1.oxidoreductase: transfer H and O atoms or electrons
2.transferase: transfer functional groups
3.hydrolase: hydrolysis
4.lyases: removes groups of substrates
5.isomerases: isomerizaton changes within a molecul
6.ligases: join together 2 molecules
7.translocases: catalyse movement of ions accorss membranes
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Chymotrypsin
-breaks down protein
-is a protease
-cleaves peptide bond adjacent to aromatic CC
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Lysozyme
-antibacterial enzyme found in saliva, tears, mucus
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Peptidoglycan
-polysaccharide found in bacterial cell walls
-cleavage leads to destruction of bacteria
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Factors that influence enzymatic activity
-temperature, pH, concentration
-higher temperature, faster reaction
-optimum pH range
-increase in enzyme concentration, faster reaction
-increase in substrate concentration increases rate of reaction
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Non-specific activity regulation
-needs enzyme and substrate
1. increasing substrate will increase rate of reaction
2. temperature increase will increase activity to optimal rate
3. pH changes enzyme structure
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Specific enzyme activity regulation
1. activation by proteolytic cleavage: enzyme is secreted in inactive form (ZYMOGEN)
-proenzyme zymogen is activated by removing part of the enzye by cleaving the peptide bond (irreversible)
-this enzymatic activation is seen in protein digesting enzymes
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Activation of trypsinogen
-trypsinogen is made in the pancreas
activation:
-N terminus covers the active site
-trypsinogen is secreted from pancreas into duodenum where enterokinase cleaves the N-terminus
-active site is exposed and the enzyme can start to cleave the protein
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Regulation by covalent modification
-attaching structures to an enzyme with a covalent bond
examples:
-phosphorylation
-adenylation
-acetylation
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Allosteric sites
-allow effectors to bind to the protein resulting in conformation change
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Allosteric activators
-bind to locations on an enzyme away from the active site, inducing a conformational change that increases the affinity of the enzyme's active site for its substrate
-work in feed back and feed forward loops
-feed back: production is stopped when product is made (enzyme is inhibited)
feed forward: beginning of pathway would increase activity of next enzyme
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Competitive inhibition
-inhibitor competes with substrate for binding
-does not effect catalysis
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Uncompetitive inhibition
-inhibitor only binds to ES complex
-inhibits catalytic function
-does not affect substrate binding
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Mixed inhibition
-inhibitor binds to enzyme with or without substrate
-binds to regulatory site
-inhibits substrate binding and catalysis
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ie. of metabolic pathway
-glycolysis
purposes:
-extraction of energy
-storage of fuels
-synthesis of important building blocks
waste elimination
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Ubiquitin
-regulatory protein
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Ubiquitylation
-ubiquitin protein is attached to a substrate protein
-affects proteins in many ways ie can mark them for degradation
-regulates various cellular processes, including immune response, angiogenesis, cell proliferation, apoptosis, and DNA repair
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Commited step
-enzyme that commits molecule to a pathway
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Regulation from outside the cell
-HORMONES!!
-cell receives signals and react to these by activaing enzymes or gene expression
-hormones can chnge substrate availability
-Insulin signals insulin receptor and vesicle containing glucse transportase will be released and infused with the membrane
-epinephrin binds to receptor
-G protein activated cAMP
-cAMP activates PKA kinase
-PKA kinase activates another kinase
-regulatory enzymes is activated for glyogen cleavage
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Vitamins
-micronutrients
-fat soluble ones stored in tissues: A, D, K, E
-water soluble: B1, B2, 3, 5, 6, 7, 9, 12, C
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Digestive system
1. mouth chews food, mixes it with saliva
2. salivary gland produces saliva containing starch and amylase
3. pharynx swallos the food
4. esophagus moves the bolus to the stomach
5. stomach mixes food with gastric juice that contain acid pepsin and chyme is created
6 .liver makes the bile which digests fat
7. pancreas releases bicarbonate to neutralize intestinal contents
8. gall bladder stores bie and releases it into small intestine
9. small intestine digests food and absorbs nutrients into blood
10. large intestine absorbs water, vitamins and minerals and passes waste material
11.anus, waste laves the body
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Saliva
-pH 6.8-7.2
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Gastric juice
-stomach
-combination of hydrochloric acid (HCl), lipase, and pepsin
-secreted by parietal cells, chief cells and mucus cells
-pH 1-2
-3 functions: kill micro organisms, denature dietary proteins, required for actio of pepsin
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H+ acid secretion
-H+ ions are formed inside parietal cells from the dissociation of carbonic acid
-Cl- is pumped inside the parietal cell in exchange of HCO3
-H+ ions are pumped into gastric lumen by K+/H+ATPase
-Cl- moves out of parietal cell into lumen through electrical gradient
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Gastrin
-it is a hormone secreted from G-cell in stomach
-regulates acid production
-gatric secretion is stimulated by proteins, peptides and AA
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Pancreactic juice
-secreted by pancreas
-consists of fluid and enzymes trypsin, lipase, and amylase (essential for the digestion of most of the protein, fat, and carbohydrate)
-pH 7-6-8.3
-is alkanine and therefore has ahigh concentration of bicarbonate ions which neutralize acidic gastric acid
-secretion is regulated by the release of secretig and CCK (cholecystokinin from duodenum)
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CCK (cholecystokinin)
-is a digestive hormone
-released with secretin when food from the stomach reaches the first part of the small intestine (duodenum)
-stimulates the gallbladder to contract and release stored bile into the intestine
-stimulate pancreatic secretion and inhibits food intake
-produced by enteroendocrine cells of proximal small intestine
-secretion is stimulated by polypeptides and AA
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Secretin
-peptide hormone
-secreted by mucosal cell (in duodenum)
-acts on the pancreas where it stimulates the release of bicarbonate and water
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Intestinal juice
-in the small intestine
-pH 7.1-7-6
-neutralizes hydrochloric acid coming from the stomach-
-releases gastrointestinal hormones into the bloodstream
-contains digestive enzymes that facilitate the digestion and absorption of food
-mechanical stimulation produced by the presence of food
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digestion of carbohydrates
-During digestion, starches and sugars are broken down both mechanically (chewing) and chemically (by enzymes) into the single units glucose, fructose, and/or galactose, which are absorbed into the blood stream
2 phases:
-luminal phase: intraluminal hydrolysis of starch to oligosaccharides by salivary and pancreatic amylases
membrane phase: membrane digestion of oligosaccharides to monosaccharides by brush border enzymes
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saliva
-contains alpha amylase (endoglycosidase)
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brush border enzymes
1. glycoamylase
-exoglycosidase
-> products: shorter oligosaccharides
-> initiates cleavage at non-reducing end of sugar
2. sucrase-isomaltase complex
-exoglycosidase
-sucrase hydrolyses bond between glucose and fructose
3.beta-glycosidase
-has two catalytic sites
4.trehalose
-absolute specific to substrate
-can only cleave alpha 1,4 bonds
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GLUT2
-facitilated glucose transport
-glucose moves via facilitated transporter from high to low concentration the blood (no ATP needed)
70
fructose malabsorption
-the cells of the intestine cannot absorb fructose normally, leading to bloating, diarrhea or constipation, flatulence, and stomach pain
-due to reduced abundance of GLUT-5 transporter on the surface of the intestinal brush border membrane
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pepsin
-enzyme in gastric juice that digests proteins
- gastrin and secretin stimulate the release of pepsinogen into the stomach, where it is mixed with hydrochloric acid and converted to the active enzyme pepsin
-pH 1.2
-inactive at pH above 5
-In the intestine the gastric acids are neutralized (pH 7), and pepsin is no longer effective
-endopeptidase
-cleaves peptide bond after aromatic AA from N-terminus
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Pancreas secretes
-trypsin
-chymotrypsin
-elastase
-carboxypeptidases A,B
73
absorption of AA
-AA are transported from lumen into cell by Na+ AA cotransporters in the apical membrane
-6 different Na-dependent AA carriers are located in the apical brrush border membrane of the epithelial cell
-AA are then transported across the basolateral membrane into blood by facilitated diffusion
di and tripeptides are transported by separate H+ dependent cotransporters
-once inside the cell the di and tripeptides are hydrolysed to AA by cytosolic peptidases
74
defect in apical A transport
-hartnup disease (L-tryptophan) and cystinuria (L-alanine)
-heriditary diseaes
-autosomal resessive
-associated with small intenstine and renal tubule abnormalities in absoprtion of neutral aA
75
Lipids in foods
-energy reserve
-reguate hormones
-transmit nerve impulses
transport fat-soluble nutrients
1.triacylglycerides
2.phospholipids
3.galactolipids
4.cholesterol ester
76
Lingual lipase
-lipid digestion enzyme in the oral cavity
-important in milk fat digestion in newborns
-cleaves fatty acyl ester at position 3
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Gastric lipase
-secreted by chief cells
-has low optimum pH 4-6
-cleaves fatty acyl ester bod at position 3
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pancreatic TAG lipase
-secreted as an active enzyme
-needs cofactor COLIPASE
-hydrolyses ester bods of TAGs at first and third position of glycerol backbone
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colipase
-is a protein co-enzyme required for optimal enzyme activity of pancreatic lipase
-secreted in pancreatic juices in inactive form "Procolipase"
-restores the activity of pancreatic lipase and prevents from furhter inhibition by bile salts
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Phospholipase A2
-pancratic enzyme
-secreted as a proenzyme and is activated by trypsin
-hydrolyses phospholipids to lysolecithin
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pancreatic lipase related to protein 2
-hydrolyses galacto lipids
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carboxyl ester lipase
-lipolytic enzyme capable of hydrolyzing cholesteryl esters, tri-, di-, and mono-acylglycerols, phospholipids, lysophospholipids, and ceramide
-secreted as an active enzyme
-(lipase is an enzyme the body uses to break down fats in food)
-hydrolyses cholesterol ester to free cholesterol and fatty acids
83
bile
-produced by liver, stored in gall bladder
-consists of bile salts, proteins, electrolytes, cholesterol, fatty acids, bilirubin
-excretes toxins, heavy metals, drugs etc
-has a digestive functions by breaking down food
-absorbative function of absorbing lipids
-emulsify lipids
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Lipid emulsification by bile salts
1. fat globues are large, have hydrophillic properties and therefore lipase can only cleave the surface
2. to increase the rate at which lipas cleaves the ester bonds, liver releases bile
3. bile enters the small intestine where it mixes with fat globules ad breaks into smaller units called "emulsion droplets"
4.emulsification increases the surface area of fat on which lipase can act on
5. now lipase can begin digesting the ester bonds
6.lipase and colipase bind to the surface of emulsion droplets and break them down into fatty acids
85
synthesis of bile acid (BA)
-made in the liver (needs 17 enzymes)
-made from cholesterol
-synthesis happens in many intracellular compartments ie. cytosol, ER, mitochondria, peroxisomes
-from cholesterol we get 2 primary bile acids
-bile acids are secreted into the lumen and are conjugated with glycine or taurine
-conjugation lower pKa of bile salts and makes them better detergents
-conjugation increases amphiphatic nature of the bile acids, making them more easily secretable
-after conjugation, sodium and potassium ions cans be attached to bile acids increasing the solubility o bile salts
-bile salts are secreted into the duodenum and emulsified
-they are then reabsorbed into the ileum
-small portion of bile salts are nor reabsorbed and are deconjugated (AA removed) and dehydroxylated (secondary bile acid)
-this is a bacterial defense mechanism to lethalise activiy of bile
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Lipid transport
-AA and monosaccharides enter the hepatic portal vein and travel to the livere
-in the liver, AA are used for protein synthesis and monosacchardies are used for glycogen production
-lipid digestion products enter the lymphatic capillaries, which travel to the left subclavian vein and enter blood circulation
