Biochemistry Exam 2
Write the net equation of anaerobic glycolysis as it occurs in muscle tissue.
Glucose + 2 ADP + 2 Pi--> 2 lactate + 2 ATP + 2 H2O + 2 H+
overall reaction of glycolysis
Glucose + 2NAD+ +2ADP + 2Pi -> 2 Pyruvate + 2NADH +2ATP + 2H2O + 4H+
Three reactions in glycolysis operate far from equilibrium and are potential sites for major flux control. List the three enzymes and discuss why each enzyme is or is not the major control site of glycolysis.
Hexokinase catalyzes the first exergonic step of glycolysis. However, when the source of glucose-6-phosphate is from glycogen in skeletal muscle, rather than free glucose, the hexokinase reaction is not required. Pyruvate kinase catalyzes the last reaction of glycolysis and is therefore not a good candidate for regulation of the entire pathway.Phosphofructokinase catalyzes a very exergonic reaction at Step 3. This is near the beginning of the pathway, but after the entry of glucose-6-phosphate from glycogen, so it can regulate the entire pathway.
what are stages for extracting energy from food
1) Large food molecules are broken down into smaller units, such as amino acids, carbohydrates, and fatty acids. 2) The small units are further broken down to a subset of small molecules that are critical to metabolism, such as acetyl CoA. 3) ATP is produced by oxidation of the acetyl units.
catabolism produces what compounds for energy utilization?
1. ATP 2. other compounds with high phosphoryl transfer potential 3. reducing power (NADPH, NADH, FADH2)
How many high energy bond(s) does ADP have? A. 1 b. 2 c. 3 d. 0
A
What are the principal ways by which metabolic pathways are regulated? a. The amount of enzymes, the enzyme catalytic activities, and substrate accessibility & supply b. Enzyme synthesis, degradation, gene expression c. Allosteric regulation, reversable covalent modification, phopsphorylation d. Allosteric regulation, phopsphorylation, substrate accessibility & supply
A
What is substrate level phosphorylation?
ATP synthesis when the phosphate donor is a substrate with high phosphoryl transfer potential
During glycolysis, the steps between glucose and formation of the triose phosphates: A) consume two ATP and two NADH molecules. B) consume two ATP molecules. C) produce two ADP and two NAD+ molecules. D) produce two ATP and two NADH molecules. E) consume two NADH molecules.
B
In which of the following metabolic conversions is ATP "consumed" during glycolysis? A) 1,3-Bisphosphoglycerate = 3-phosphoglycerate B) Glucose =glucose-6-phosphate C) 2-Phosphoglycerate = 3-phosphoglycerate D) Fructose-1,6-bisphosphate = dihydroxyacetone phosphate + glyceraldehyde-3-phosphate E) Glucose-6-phosphate = fructose-6-phosphate
B
Which is the net equation of glycolysis as it occurs in aerobic cells such as brain cells? A) Glucose + 2 ATP = 2 lactate + 2 ADP + 2 Pi B) Glucose + 2 ADP + 2 Pi + 2 NAD+= 2 pyruvate + 2 ATP + 2 NADH + 4 H+ C) Glucose + 2 ADP + 2 Pi= 2 lactate + 2 ATP + 2 H+ D) Glucose + 2 ADP + 2 Pi= 2 CH3CH2OH + 2 CO2 + 2 ATP E) Glucose + 2 ADP + 2 Pi + 2 NAD+= 2 lactate + 2 ATP + 2 NADH + 4 H+
B
Which of the following are produced in anabolism? a. NAD+ b. NADPH c. ADP + Pi d. FADH2 e. ATP
C
feed-forward activation
Metabolite early in the pathway activates an enzyme further down the pathway
Why do muscles need to generate ATP under aerobic and anaerobic conditions?
Muscles initially function aerobically. However, when bursts of energy are required, the oxygen supply does not meet the demand. In order to generate sufficient ATP for energy demands the muscle depends on activity-dependent anaerobiosis.
galactose ( 6 aldose)
a component of lactose in milk
Phosphofructokinase (PFK) regulated
a key rate-limiting enzyme of the anaerobic glycolytic energy system - high levels of ATP inhibit its activity - high levels of AMP increase its activity a decrease in ATP/AMP = low cell energy= stimulates glycolysis
lactate fermentation: during strenuous exercise...
buildup of lactate in tissues as the oxygen supply becomes inadequate decrease in pH causes muscle pain and cramps also decreases blood pH - breath heavy and deep
the two processes of metabolism are linked by what?
by producing and consuming ATP and reducing power
how are metabolites with high phosphoryl transfer potential involved in metabolism?
can donate phosphoryl group to ADP to form ATP
major components of cell walls
cellulose, hemicellulose, lignin, pectin polysaccharides
how're metabolic processes unified?
common molecules such as ATP and oxidation/reduction rxns
deoxyribose (5 aldose)
component of dna
ribose (5 aldose)
component of rna, coenzymes
Polysaccharides
composed of many monosaccharide units 1. starch (plants) = amylose a(1,4) and amylopectin a (1,4) & a (1,6) 2. glycogen (animals) a (1,4) & a (1,6) 3. cellulose (plants) B (1, 4)
Gluconeogenesis
consumes 6 high energy bonds in making one glucose from 2 pyruvate 2 pyruvate + 4 ATP + 2 GTP +2NADH +6 H20--> GLUCOSE +4 ADP + 2 GDP +6 Pi +2NAD+ +2H+ place of synthesis : liver endergonic process that requires energy glycolysis is exergonic
why is atp a high energy compound?
contains two phosphoanhydride bonds that are unstable due to electrostatic repulsion, resonance instability, and stabilization due to hydration
anomer (a & b)
cyclic sugars that differ only in positions of substituents at the hemiacetal or hemiketal carbon a = the -OH group attached to the hemiacetal or hemiketal C is below the plane of the ring B= the -OH groups is above the plane of the ring
artery blockage
decreases oxygen supply, increasing glycolysis and lactate levels, produces cramps, stops beating (cardiac arrest)
relationship between electromotive force and delta G of reaction?
delta G = -nFe
Most monosaccharides are chiral compounds
enantiomers - mirror images diasteromers - different configurations but not mirror images, one or more stereocenters epimers - differ from each other by one stereocenter **D-sugars predominate in nature
what is the purpose/ use of glycolysis
energy production (ATP, NADH) a. substrate level phosphorylation : formation of atp under anaerobic conditions b. produce substrate for oxidative phosphorylation (respiration)
phosphagens
energy-rich storage molecules in animal muscle ex. phosphocreatine & phosphoarginine = phosphoamides have higher group-transfer potential than atp , used to replenish atp when needed via creatine kinase reaction
why are two different e- carriers , nad+ and fad, involved in metabolism?
fad is involved in one- electron transfers and two-electrons transfers; higher standard reduction potential than nad+ nad+ is involved in ONLY two- electron transfers
Regulation of Gluconeogenesis
fructose - 1,6- bisphosphate is the key enzyme regulation : atp high , enzyme activity increases, and gluconeogenesis increases amp levels high (atp low), enzyme activity increase, glycolysis increases
Fructose (6 Ketose)
fruit sugar, honey syrup
what two 3-carbon molecules are generated by the cleavage of fructose -1,6 bisphosphate?
glyceraldehyde-3-phosphate and dihydroxyacetone phosphate
how many atp and nadh are produced from one glucose molecule?
4 atp 2 nadh
why are the vitamins niacin (b3) and riboflavin (b2) necessary for metabolism?
these are NOT synthesized in humans, but are components of coenzymes requires for redox reactions in metabolism niacin - nad+ riboflavin - fad
why is fermentation important to the cell?
to regenerate nad+ so glycolysis can continue
disaccharides
two simple sugar linked by a glycosidic bond ex. lactose (milk sugar) -- reducing sugar maltose (malt sugar) -- reducing sugar sucrose (cane sugar) -- nonreducing sugar
NAD+ is required for the oxidative step glycolysis. Briefly discuss how NAD+ is regenerated from NADH under aerobic and anaerobic conditions in skeletal muscle.
under aerobic conditions, electrons pass from the reduced coenzyme (NADH) through a series of electron carriers to oxygen, the final oxidizing agent. This regenerates the oxidized coenzyme (NAD+). Under anaerobic conditions, the electrons of NADH are transferred to pyruvate to form lactate, the end-product of glycolysis under anaerobic conditions.
cori cycle
working muscles utilize glucose to produce lactate, which is released to the blood, transported to the liver and converted back to glucose in the liver. glucose in the liver is released to the blood and transported back to the muscle. glucose usage and replenishment
4 ways cells control/ regulate flux?
1. allosteric control of rate- determining step 2. covalent modification of enzymes to activate or deactivate them 3. substrate cycles in which two opposing reactions are catalyzed by different enzymes 4. genetic control to alter amount of enzymes in response to cellular needs
features of metabolic pathways
1. forms = linear , cyclic, spiral 2. discrete steps = multistep pathways w multiple enzymes 3. regulated = 1) the amount of enzymes - synthesis/degradation (transcription/ expression) 2) enzyme catalytic activities - allosteric regulation , reversible covalent modification (de- phosphorylation) 3) accessibility and supply of substrates 4. compartmentalized - permits separate pools of metabolites within a cell, simultaneous operation of metabolic paths, high local concentrations of metabolites, coordination regulation of enzymes
carb nomenclature
1. functional group = aldose or ketose 2. # of carbons = 3c - triose , 4c - tetrose , 5c - pentose, 6c - hexose
what does a high-energy compound mean?
1. greater free energy of hydrolysis than a typical compound 2. contains one or more very reactive bonds that require less energy to break
properties of chiral molecules
1. physical properties of enantiomers are identical except different optical activity (rotate the plane of polarization of light) 2. enantiomers have identical chemical properties toward all reactions whose molecules are achiral 3. enantiomers react differently toward reactants whose molecules are chiral
common properties of lactate and alcohol fermentation
1. pyruvate as a substrate 2. oxidize nadh to nad+ 3. self-limiting process
how many net atp molecules are produced from 1 glucose under anaerobic conditions
2 atp
importance of ATPs intermediate phosphoryl group-transfer potential to energy metabolism in cell?
ATP formed from ADP by transfer of phosphoryl groups from compounds with higher- phosphoryl group transfer potentials. The ATP then transfers a phosphoryl group to compounds with lower phosphoryl group-transfer potentials
How is glycolysis maintained under anaerobic conditions?
Pyruvate can be reduced to either lactate or ethanol, and this reaction is accompanied by the oxidation of NADH to regenerate NAD+
Accumulation of which of the following compounds is the cause of stiff and sore muscle after vigorous exercise? a. pyruvate b. acetyl-CoA c. ethanol d. lactic acid e. glycerate
D
In skeletal muscle cells, the NADH that is produced by glycolysis under anaerobic conditions (vigorous exercise) is regenerated to NAD+ by the conversion of: A) acetaldehyde to ethanol. B) lactate to pyruvate. C) phosphoenolpyruvate to pyruvate. D) pyruvate to lactate. E) glyceraldehyde-3-phosphate to 1,3-bisphosphoglycerate.
D
Which of the following are produced in catabolism? a. NAD+ b. NADP+ c. FAD d. FADH2 e. all the above
D
Which of the following is at a higher level of oxidation than CH3CHO? A) CH3CH2OH B) CH3CH3 C) CH2=CH2 D) CH3CO2H E) none of the above
D
Which of the following metabolic conversions is considered to be the major control point of glycolysis? A) Fructose-1,6-bisphosphate --> dihydroxyacetone phosphate + glyceraldehyde-3-phosphate B) Glucose --> glucose-6-phosphate C) 2-phosphoglyerate --> phosphoenolpyruvate D) Fructose-6-phosphate --> fructose-1,6-bisphosphate E) pyruvate --> lactate
D
. Molecule(s) with a higher phosphoryl transfer potential than ATP: a. phosphoenolpyruvate b. creatine phosphate c. 1,3 bis-phosphoglycerate d. a and b e. a, b, and c
E
In eukaryotes, the enzymes that catalyze the reactions of glycolysis are located in: A) the cell nucleus. B) the endoplasmic reticulum. C) the mitochondria. D) the lysosomes. E) the cytosol.
E
The major purpose(s) for which organisms require energy: a. performance of mechanical work b. active transport c. synthesis of biomolecules d. a and c e. d. a, b, and c
E
What is the purpose of phosphorylating glucose in cytosol? a. to trap glucose in the cell b. to destabilize glucose and facilitate the next series of metabolic steps c. to convert it to a more soluble form d. all of the above e. a and b
E
Which of the following are used in biosynthesis processes? a. NADH b. NADPH c. ATP d. all the above e. a and c f. b and c
F
The ethanol formed naturally by alcoholic fermentation is usually 5-12%, which is much lower than the concentration in distilled liquors. Why?
Organisms such as yeast, which are responsible for the ethanol production, can only tolerate low levels of alcohol. Higher levels would be toxic to live cells.
Why is it more sensible for phosphofructokinase to be an important control step, rather than hexokinase?
Phosphofructokinase catalyzes the first committed step in the glycolytic pathway. At this point, the molecule is committed to entering the glycolytic path. In contrast, production of G6P is the first step in many different paths. Thus, glycolytic control would not be maintained by tight regulation of hexokinase.
lactate fermentation
Pyruvate --(NADH-> NAD)-> Lactate
phosphoryl-group - transfer potential
The ability of a compound to transfer its phosphoryl group high-energy compounds : have group transfer potentials equal to or greater than that of ATP ex. phosphocreatine, phosphoenolpyruvate low energy compounds: have group transfer potentials less than that of atp ex. glucose- 6 phosphate
how does glycolysis produce energy?
substrate level phosphorylation: formation of ATP by transferring a phosphate group from a substrate of a reaction to ADP oxidative phosphorylation : the process in which ATP is formed as a result of the transfer of electrons from NADH or FADH 2 to O 2 by a series of electron carriers.
sucrose
a1 --> B2 of -D-glucose and -D-fructose nonreducing sugar because both -OH groups are used in glycosidic bond formation
carbohydrate general structure
aldehydes or ketones with at least two hydroxyl (OH-) groups = aldoses and ketoses composed of C,H, O formula = (CH2O)n n>=3 simplest carbs = glyceraldehyde & dihydroxyacetone`
glycolysis
an ANAEROBIC pathway in which 1 glucose (6C) is converted to 2 pyruvate (3C) molecules with production of 2 ATP and 2 NADH
metabolism as two processes, how are they unified?
anabolism and catabolism unified through production and consumption of ATP and reducing powers such as NAD(P)H. Catabolism degrades molecules to produce ATP and reducing power. Anabolism uses ATP and reducing power to synthesize molecules.
proteoglycans
animal cell surface and in the extracellular matrix; unbranched heterglycans of repeating disaccharides
lignin
aromatic polymers resulting from oxidative coupling of 4 hydroxylphenylpropanoids
gluconeogenesis
synthesis of glucose from noncarb precursors such as lactate, glycerol, and amino acids noncarbs (pyruvate) ---> glucose
glucose (6 aldose)
grape sugar, blood sugar, dextose
glycoside formation
hemiacetal/ hemiketal +alcohol --> acetal/ ketal involves joining the hydroxyl group of the hemiacetal and another hydroxyl group of another compound by dehydration
two regulatory steps in glycolysis
hexokinase --> glucose+atp = glucose -6 - pi +adp pyruvate kinase --> phosphoenolpyruvate +adp = pyruvate +atp
glycolysis as two stages:
hexose stage: 2 atp consumed per glucose triose stage: 4 atp are produced per glucose net : 2 atp
which metabolic reaction is most commonly used to break down food?
hydrolysis reactions
lactose
lactose B (1,4) reducing sugar because of the presence of a free hemiacetal - OH
peptidoglycans
major component of bacterial cell walls composed of alternating n-acetylglucosamine and n-acetylmuramic acid
maltose
maltose a (1,4) reducing sugar because of the presence of a free hemiacetal -OH two D-glucose
cellulose
most abundant , key source for biomass-based renewable energy structural component of plant cell walls human cannot digest bc lack of cellulase
Briefly discuss the hypothesis that increased consumption of high fructose corn syrup is linked to the increase of obesity.
n the liver, fructose is converted to fructose-1-phosphate by fructokinase. Fructose-1-phosphate is then cleaved to glyceraldehyde and dihydroxyacetone phosphate by a specific aldolase. These products are then converted to glyceraldehyde-3-phosphate. These reactions bypass phosphofructokinase, the key regulatory step of glycolysis. Under normal conditions, elevated ATP would decrease the glycolytic flux. However, high fructose in the diet bypasses this control, and the glycolytic flux can be directed toward fat synthesis instead.
reduced coenzymes conserve energy from biological oxidations
nadh used for atp synthesis nadph used for reductive biosynthesis fadh2
why are vitamins niacin and riboflavin necessary?
niacin is a component of NAD+ and riboflavin is a component of FAD --- components of redox reactions
glycoproteins
oligosaccharide chains exhibit great variability in sugar sequence and composition
where does body's energy come from?
oxidation of carbon releases energy most energy = methane > methanol> formaldehyde> formic acid> co2 = least energy
ATP
the cellular energy currency --- energy released from foods ATP contains two high energy bonds, and hydrolysis of ATP yields energy
major differences between primary and secondary cell walls
primary cell wall is made of mostly pectin polysaccharides, whereas secondary cell wall is made of cellulose, hemicellulose, and lignin
feedback inhibition
product of a pathway controls the rate of its own synthesis by inhibiting an early step
dietary fibers
provide bulk which help the body get rid of waste, give feeling of fullness while providing few calories reduce the risk of colon cacer, heart attack, adult diabetes, affect microbiota
what is atp hydrolysis used for in metabolic reactions
provides energy for endergonic processes
what is atp used for in metabolic reactions?
provides energy to drive endergonic processes by cleavage of both phosphoanhydride bonds
advantage of pyrophosphate cleavage of ATP
pyrophosphate cleavage of ATP produces PPi as one of the end products. then, inorganic pyrophosphatase catalyzes the exergonic hydrolysis of PPi -> 2Pi --- supplies sufficient free energy to drive endergonic process
what happens to pyruvate under aerobic conditions?
pyruvate + coenzyme a +nad+ = acetyl-coA +co2 +nadh glucose -> 2 pyruvate ->2 acetyl coa-> 6CO2 + 36 ATP
vitamin supplements for low carb diets contain higher amounts of biotin, why?
pyruvate decarboxylase requires biotin. high levels of supplemental biotin would promote glucose synthesis
alcohol fermentation
pyruvate is converted to ethanol in two steps: 1. pyruvate to acetaldehyde via pyruvate decarboxylase 2. acetaldehyde to ethanol via alcohol dehydrogenase
how is reduction potential related to free- energy
reduction potential = measure of its thermodynamic reactivity n = # of e transferred F= faraday constand 96.48 kj/v e = electrical potential difference = acceptor - donor