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Flashcards in Chapter 8 Deck (37)

What is the general structure of an amino acid?


What are the hydrophobic amino acids?

nonpolar aliphatic side chains: Glycine (Gly), Alanine (Ala), Valine (Val), Leucine (Leu), Isoleucine (Ile), Proline (Pro)

aromatic side chains: phenylalanine (Phe), Tyrosine (Tyr), Tryptophan (Trp)


What can phenylalanine and tyrosine form?



What can tryptophan form?

serotonin, niacin 


What amino acids are metabolized normally in maple syrup urine disease?

valine, leucine, and isoleucine


What is the significance of proline?

secondary amine, whose presence in a protein disrupts normal secondary structure 


What are the hydrophilic amino acids?

positively charged R groups: lysine (Lys), Arginine (Arg), Histidine (His)

negatively charged R groups: Aspartate (Asp), Glutamate (Glu)

polar, uncharged R groups: Serine (Ser), Threonine (Thr), Cysteine (Cys), Methionine (Met), Asparagine (Asn), Glutamine (Gln)


What do hydrophilic side chainns contain?

O or N atoms


What are the charges of acidic amino acids and basic amino acids?

acidic (aspartic and glutamic acids): carboxyl groups are negatively charged at physiologic pH

basic (lysine, arginine, histidine): nitrogen atoms are positively charged at physiologic pH


What amino acids are sites for O-linked glycosylation of proteins  and where does this occur?

serine and threonine

posttranslation modification associated with the Golgi apparatus 


What is the site for N-linked glycosylation of protein and where does it occur?



posttranslational modification that is associated with the ER


What is the significance of cysteine?

contains sulfur and can form disulfide bonds, which stabilizes tertiary structure 

destroying disulfide bonds denatures proteins 


What is the significance of methionine?

sulfur-containing amino acid

part of S-adenosylmethionine (SAM), methyl donor in biochemical pathways 


What is sickle cell anemia characterized by?

severe pain in bones, abdomen, chest, and periods of hemolytic problems

vaso-occlusive pain lasting 1 week

crises precipitated by dehydration or infection


What mutation occurs in sickle cell anemia (HbS) and sickle cell anemia-like hemoglobinpathy (HbC)?

HbS: substitution of valine for glutamate at position 6 of Hb

--HbS has one less negative charges overall compared with HbA

HbC: substitution of lysine for glutamate at position 6

--HbC has two more positive charges compared with HbA


What is protein turnover?

When broken down proteins are replaced


How are proteins broken down?

lysosomal proteases digest endocytosed proteins

large cytoplasmic complexes (proteasomes) digest older or abnormal proteins that have been covalently tagged with a protein (ubiquitin) for destruction


What are the essential amino acids?

Amino acids that can't be synthesized in humans and must be provided by dietary sources

arginine (only during periods of positive nitrogen balance, growth), histidine, isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan, valine 


What is nitrogen balance?

Normal condition where amount of nitrogen incorporated into the body each day = amount excreted


Waht is negative nitrogen balance?

when nitrogen loss exceeds incorporation

ex. protein malnutrition (kwashiorkor), dietary deficiency of even one essential amino acid, starvation, uncontrolled diabetes, infection


What is positive nitrogen balance?

amoung of nitrogen incorporated exceeds the amoung excreted

associated with: growht, pregnancy, recovery phase of injury or surgery, recovery from condition associated with negative nitrogen balance 


What is the difference between kwashiorkor and marasmus?

marasmus: chronic deficiency of calories

kwashiorkor: edema


What is ∆G?

amount of energy required or released per mole of reactant

tells you nothing about rate of reaction


What is the rate of the reaction determined by?

energy of activation ∆G†, which is the energy required to initiate the reaction

increased by enzymes

enzymes decrease energy of activation ∆G†


What effect do enyzmes have on the reaction?

lower the energy of activation

don't affect the value of ∆G or the equilibrium constant for the reaction Keq


Describe different values of ∆G.

∆G < 0: thermodynamically spontaneous (energy released, often reversible)

∆G > 0: thermodynamically nonspontaneous (energy required)

∆G = 0, reaction at equilbrium (freely reversible)

∆G0 = energy involved under standarized conditions


What is the Michaelis-Menten equation?

V = k2 [E][S] / Km + [S]

[E] constant: V = Vmax[S] / Km + [S]


What is Vmax?

Vmax = k2[E]

maximum rate possible to achieve with a given amount of enzyme

only way to increase Vmax is to increase [E]

done in cell by inducing expression of gene encoding of the enzyme


What is Km?

Substrate concentration required to produce half the maximum velocity

measure of the affinity of the enzyme for its substrate 

higher Km=enzyme has lower affinity for substrate

intrinsic property of enzyme; can't be altered by changing [E] or [S]


What is the Lineweaver-Burk equation?

reciprocal form of Michaelis-Menten equation

1/V = (Km/Vmax)(1/[S]) + (1/Vmax)

y intercept: 1/Vmax

x intercept: -1/Km


What are competitive inhibitors?

resemble substrate and compete for binding to the active site of the enzyme

increase Km, no effect on Vmax


What are noncompetitive inhibitors?

don't bind to active site 


What occurs to the Lineweaver Burk plot when more enzyme, activator or covalent modification of the enzyme is added?

Km might decrease and/or Vmax might increase when activator or covlent modification is added


What are examples of drugs that are competitive inhibitors?

Statins (lovastatin, simvastatin): control blood cholesterol

--inhibit 3-hydroxy-3-methylglutaryl coenyme A (HMG CoA) reductase in cholesterol biosynthesis

Methotrexate: antineoplastic drug 

--inhibits dihydrofolate reductase, depriving cell of active folate needed for purine and deoxythymidine synthesis-->interference with DNA replication during S phase



What are cooperative enzymes?

sigmoid kinetics

multiple subunits and active sites

regulatory enzymes in pathways

multiple sites for activators and inhibitors

Sometimes called allosteric enzymes--shape changes are induced or stabilized by binding substrates, inhibitors and activators 


How is methanol poisoning treated?

ethanol administration

both are substrates for alcohol dehydrogenase (ADH)

ethanol has lower Km for enzyme than methanol

prevents methanol from being converted to formaldehyde which is toxic and not metabolized further 


What is transport kinetics?

Km: solute concentration at which the transporter is functioning at half its maximum activity