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Test 3 Study Guide General Material for Biochemistry | CH 409, Study notes of Biochemistry

Athens State UniversityBiochemistry
Prof. Nancy Mcdonald

Test 3 Study Guide General Material Material Type: Notes; Professor: McDonald; Class: Biochemistry; Subject: Chemistry; University: Athens State University; Term: Spring 2011;

Typology: Study notes

2010/2011

Uploaded on 03/27/2011

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Biochemistry Test 3
Ch 7
1. Enantiomers: either pair of chemical compounds whose molecular structures have a non-
superimposable mirror-image relationship.
Diastereomers: stereoisomer of a compound having 2+ chiral centers that is not a mirror
image of another stereoisomer of the same compound/
If a molecule contains a single asymmetric carbon atom, it is will have two mirror image forms. If a
molecule contains two asymmetric carbons, there are 4 possible configurations, and they can’t all be
mirror images of each other. The possibilities continue to multiply as there are more asymmetric centers
in a molecule. EX. Tartaric acid contains two asymmetric centers.
The families of 5 and 6 carbon sugars contain many diastereomers because of the large numbers of
asymmetric centers in these molecules.
Epimers: a stereoisomer that has a different configuration at only one stereogenic center.
A hemiacetal is a functional group or compound containing the alkylgroup in the form of:
where R and R' are any carbon backbones.
A hemiacetal can react with an alcohol under very acidic conditions to form an acetal, and can dissociate
to form an aldehydes and ketones.
Anomers: In sugar chemistry, an anomer is a special type of epimer. It is a stereoisomer of
a saccharide (in the cyclic form) that differs only in its configuration at the hemiacetal or
hemiketal carbon.For example, α-D-glucopyranose and D-D-glucopyranose and glucopyranose and β-D-glucopyranose and D-D-glucopyranose and glucopyranose are anomers.
Mutarotation: the change in specific rotation that occurs when anα (alpha) or β
(beta) hemiacetal form of carbohydrate is converted into an equilibrium mixture of the two
forms.
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Download Test 3 Study Guide General Material for Biochemistry | CH 409 and more Study notes Biochemistry in PDF only on Docsity!

Biochemistry Test 3

Ch 7

1. Enantiomers: either pair of chemical compounds whose molecular structures have a non-

superimposable mirror-image relationship.

Diastereomers: stereoisomer of a compound having 2+ chiral centers that is not a mirror

image of another stereoisomer of the same compound/ If a molecule contains a single asymmetric carbon atom, it is will have two mirror image forms. If a molecule contains two asymmetric carbons, there are 4 possible configurations, and they can’t all be mirror images of each other. The possibilities continue to multiply as there are more asymmetric centers in a molecule. EX. Tartaric acid contains two asymmetric centers. The families of 5 and 6 carbon sugars contain many diastereomers because of the large numbers of asymmetric centers in these molecules.

Epimers: a stereoisomer that has a different configuration at only one stereogenic center.

A hemiacetal is a functional group or compound containing the alkylgroup in the form of: where R and R' are any carbon backbones. A hemiacetal can react with an alcohol under very acidic conditions to form an acetal, and can dissociate to form an aldehydes and ketones. Anomers: In sugar chemistry, an anomer is a special type of epimer. It is a stereoisomer of a saccharide (in the cyclic form) that differs only in its configuration at the hemiacetal or hemiketal carbon.For example, α-D-glucopyranose and D-D-glucopyranose and glucopyranose and β-D-glucopyranose and D-D-glucopyranose and glucopyranose are anomers.

Mutarotation: the change in specific rotation that occurs when anα (alpha) or β

(beta) hemiacetal form of carbohydrate is converted into an equilibrium mixture of the two forms.

Acetal: a functional group or molecule containing the functional group of a carbon bonded to two -

OR groups. where R, R' and R&apos are all carbon backbones.

2.Examples of epimer: glucose, mannose 229

Glycosidic linkage

Reducing sugar 235-D-glucopyranose and ALL MONOSACCHARIDES glucose

Monosaccharide: Simple sugars/ribose 228

Anomer: Hemiacetals = α- & Beta-glucose/ 231

Diastereomer: glucose and galactose

3.What structural relationship is indicated by the term D-sugar? That the position of the OH on

the last asymmetric carbon atom is on the right will tell us whether we are dealing

with a "D" sugar or an "L" sugar. "D" stands for dextro and "L" stands for levo. If the

OH is on the right, then we are dealing with a "D" sugar, in this case D-D-glucopyranose and glucose.

asymmetric carbon farthest from the aldehyde or keto group.

Why (+) glucose (shifts polarized light to the right) and (-) fructose (shifts polarized light to the

left) both classified as D-sugars?

Solutions of chiralchemical compounds change the plane in which the light is polarized. Each enantiomer

of a pair rotates the plane of the light by the same amount, but the directions of rotation are

opposite. If one enantiomer rotates the plane of the light to the left, the other rotates it to the

right.

5. Define: Alditol-Sugar alcohols 235

Epimerization-The reversible interconversion of epimers. G- 5 Enediol-intermediate formed during isomerization of monosaccharides, has a dbl bond w/ a OH--^ group on each alkenyl. G- Acetal-Formula=RCH(OR`) 2 Formed from the rxn of a hemiacetal w/an alcohol

Glycosidic linkage

2. Functions:

Insulin:298/stimulates glycogenesis and inhibits glycogenolysis EX. Lowers blood glucose levels Glucagon=298/ stimulates glycogenolysis and inhibits glycogenesis. Ex.raises blood glucose levels.

Fructose-2,6-bisphosphate=the effector molecule activates PKF-1 & stimulates glycolysis

UDP-glucose=active form of glucose/functions as a substrate for glycogen synthesis cAMP-D-glucopyranose and cyclic AMP-D-glucopyranose and 2nd^ messenger molecule produced from ATP in response to glucagon or epinephrine GSSG-D-glucopyranose and oxidized form of glutathione/activates glucose-D-glucopyranose and 6-D-glucopyranose and phosphate dehydrogenase/regulatory catalyst in pentose phosphate pathway. NADPH-D-glucopyranose and reducing agent-D-glucopyranose and lipid biosynthesis / antioxidant mechanisms

4. Where do the following occur in eukaryotic cells?

Gluconeogenesis-cytoplasm & mitochondrion

Glycolysis-265/cytoplasm

Pentose phosphate pathway-265/ cytoplasm

5. Compare the entry-level substrates, products, and metabolic purposes of glycolysis and

gluconeogenesis.

In glycolysis, the entry level substrates are sugars and the product is pyruvate. The main purposes are to

provide the cell w/energy and/or several metabolic intermediates.

The substrates for gluconeogenesis are pyruvate, lactate, glycerol, & several amino acids or α-keto-

acids.Gluconeogenesis provides the body w/glucose when blood glucose levels are low.

6 .Substrate-D-glucopyranose and level phosphorylation is the production of ATP from ADP by a direct

transfer of a high-energy phosphate group from a phosphorylated intermediate metabolic compound in an exergonic catabolic pathway.

Which 2 rxns in glycolysis are in this category?During the pay-off phase @ phosphoglycerate kinase &

pyruvate kinase steps of glycolysis.

7. The principal reason that organisms like yeast produce alcohol is b/c they utilize acetaldehyde as a

hydrogen acceptor to regenerate NAD+EX. Produces ethanol.

8. Why is pyruvate not oxidized to CO 2 and H 2 O under anaerobic conditions?B/c it’s reduced to lactate to

regenerate NAD+.

11. What effects do the following molecules have on gluconeogenesis?

All of these stimulate gluconeogenesis. Lactate/ATP/Pyruvate/Glycerol/Acetyl-CoA

AMP – inhibits gluconeogenesis

12.Describe the physiological condition that activates gluconeogenesis?The need for energy within the

cells.

13.The following 2 reactions constitute a wasteful cycle.

Glucose + ATP  glucose-6-phophate

Glucose-6-phosphate + H2O  glucose + Pi

Suggest how such wasteful cycles are prevented or controlled.

Futile cycles are prevented by having the forward and reverse reactions catalyzed by different enzymes,

both of which are independently regulated.

16.Central role of glucose in carbo metabolism:

Glucose can be a substrate or product of a number of key pathways

depending on the needs of the cell. At low energy levels glucose

undergoes glycolysis to form pyruvate and causes the electron transport

chain to produce ATP via the Krebs’s cycle.

When energy is high glucose is converted to glycogen via glycogenesis or

it may enter the pentose phosphate pathway to form pentose and other

sugars. Pyruvate formed from glucose may react to form Acetyl-D-glucopyranose and CoA. Glucose

may also be synthesized from pyruvate via gluconeogenesis from certain

amino acids.

36. In aerobic oxidation, oxygen is the ultimate oxidizing agent (electron transport). Name 2 common

oxidizing agents in anaerobic fermentation.Hydrogen &/or Fe3+,NO 3 -

38. Compare the structural formulas of ethanol, acetate, and acetaldehyde. Which molecule is the most

oxidized? Which is the most reduced? Explain:

Ethanol (less O) is the most reduced molecule and

acetate (has more O) is the most oxidized. The degree

of oxidation of an organic molecule can be correlated

with its oxygen content.

40. The consumption of large amounts of soft drink beverages and processed foods sweetened with

high-fructose corn syrup has been linked to obesity. After reviewing Fig 8.1/8.5, suggest a reason for the

phenomenon.

In high concentrations, fructose can bypass most of the regulatory steps of the

glycolytic cycle. Instead of being stored in glycogen molecules, the carbon skeletons

of excess fructose are converted through pyruvate and acetyl-D-glucopyranose and CoA to fatty acids in

triacylglycerols.

41. How does phosphorylation increase the reactivity of glucose?

The OH group is not very easily displaced. However, conversion of an OH to a phosphate ester is

very easily accomplished. These esters are good leaving groups and when displaced have the

same affect as if an OH had reacted.

42 .Examine the structure of phosphoenolpyruvate and explain why it has such a high phophoryl group

transfer potential. Because it has free energy and is coupled withOxygens to attract (+) phosphoryl

groups while conserving energy throughout the reaction processes.

Without oxygen, the ETC shuts down, and NADH accumulates at the expense of NAD+. Both high NADH and low NAD+^ levels inhibit the citric acid cycle. Low NAD+^ levels would also impact the 2 key regulatory enzymes that utilize NAD+^ as a substrate.

  1. Describe in detail the structure of Pyruvate dehydrogenase complex: Pyruvate dehydrogenase complex is a large multienzyme complex that contains 3 enzymes activities, each of which is present in multiple copies. E 1 is pyruvate dehydrogenase with TPP, E 2 is dihydrolipoyl transacetylase with lipoic acid and CoASH, and E 3 is dihydrolipoyl dehydrogenase, with NAD+^ or FAD. The pyruvate dehydrogenase complex in mammalian cells contains 60 copies of E 2 and 20-30 copies of E 1 & E 3.
  2. Describe: The roles of the each enzyme, cofactor and coenzyme of the pyruvate dehydrogenase complex are as follows: Biomolecule function/role Produces 1-Pyruvate decarboxylase---- decarboxylates pyruvate via TPP ----- HETPP and CO 2-Dihydrolipoyl transacetylase----catalyses transfer of acetyl gp ------ TPP regeneration FromHETPPto coenz.lipoic acetyl lipoic acid Note a 2nd^ transfer of this acetyl lipoic acid to coenz produces<--------acetyl-CoA &dihydrolipoyl acid 3-Dihydrolipoyl dehydrogenase------ reoxidizes dihydrolipoyl acid ------ Lipoic acid regeneration
  3. What are the 2 stages of the citric acid cycle? List the products of each stage. stage 1 rnx 1-4, two carbon atoms enter the cycles as acetyl CoA, and two carbons atoms leave the cycle as two molecules of CO 2. The products of stage 1 aresuccinyl-CoA, 2NADH, 2 CO 2 &H+ STAGE 2 RNXS ARE 5-8 OAA is regenerated from succinyl-CoA.........products of stage 2 are l- OAA,CoASH, FADH 2 , NADH, H+^ AND EITHER ATP OR GTP (we use GTP).
  4. Explain why animals cannot produce glucose from 2-carbon molecules like acetate or ethanol. Because one pathway to gluconeogenesis begins with pyruvate to form oxaloacetate (OAA) then PEP. So, decarboxylation of pyruvate to form acetyl-D-glucopyranose and CoA is not reversible and thus there isn’t a pathway from Acetyl-D-glucopyranose and CoA to pyruvate. Plus, animals don’t have a glyoxylate cycle (liberates CO 2 ) to produce 2-D-glucopyranose and carbon molecules from gluconeogenesis.
  5. What steps in the citric acid cycle are regulated and why? The steps that are regulated are those catalyzed by citrate synthase, isocitrate dehydrogenase, alpha-ketoglutarate, and alpha ketoglutarate dehydrogenase. Regulation by: allosteric effectors and substrate availability. Why? They are important metabolic branch points where acetyl-CoA synthesizes fatty acids, activates pyruvate carboxylase, and inhibits pyruvate dehydrogenase. Other reasons include formation of oxaloacetate, amino acid metabolism and other metabolic processes like PFK-1 inhibition.
  6. Provide examples of biosynthetic pathways that utilize citric acid cycle intermediates as precursor molecules. Some are: glucose & pyrimidines from oxaloacetate | purines and certain amino acids (Proline) from α-ketoglutarate| fatty acids ketoglutarate| fatty acids & cholesterol from citrate
  7. What is the significance of substrate-level phosphorylation reactions?ADP is converted to ATP by the direct transfer of a phosphoryl group from a high energy compound.

Which of the reactions in the citric acid cycle involves a substrate-level phosphorylation? This is the cleavage of succinyl-CoA to form succinate. Name another example from a biochemical pathway with which you are familiar .The glycolytic reaction that converts phosphoenolpyruvate and ADP to pyruvate and ATP.

  1. One of the many effects of chronic alcoholic abuse is thiamine deficiency, caused by impaired absorption of the vitamin through the intestinal wall diminished storage in a damaged liver. When thiamine levels are inadequate, cellular energy generation is diminished. What are the 3 enzymes involved in the cellular metabolism that require thiamine? 3 enzymes that are required thiamine are pyruvate dehydrogenase, alpha-D-glucopyranose and ketoglutarate dehydrogenase and transketolase. **Thiamine is involved in decarboxylation and acyl group transfer rxns. Absence of decarboxylation rxnsnt pyruvate from being decarbed to acetyled-CoA. The body would then lack 2 carbon units for synthesis and energy production. Pyruvate accumulates as lactate. ** Describe the metabolic consequences of inadequate thiamine levels. Thiamine deficiency includes: lack of energy/muscle wasting/acidosis.