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Biochem
Exam 2
60
Medical
Professional
03/25/2009

Additional Medical Flashcards

 


 

Cards

Term

 

How many carbons in prostaglandins?

In cholesterol?

Definition

 

20C - prostaglandins

 

27C - cholesterol

Term

 

What is the dietary precursor to prostaglandin synthesis?

Definition

 

linoleic acid

 arachidonic acid

Term

 

What are the 2 isoforms of cyclo-oxygenase? Which produce prostaglandins?

Definition

 

COX-1, COX-2

 

both produce prostaglandins

Term

 

Which COX isoform is not increased by cytokines such as IL-1?

Definition

 

COX-1

 

- constituitive

- used in cell signaling

- not influenced by steroid administration

Term

 

PGI2 opposes the action of what closely related eicosanoid through the prevention of blood clots?

Definition

 

thromboxane

 

 

Term

 

Which COX enzymes do Aspirin and Tylenol inhibit, respectively?

Definition

 

Aspirin - COX-1 and COX-2

Tylenol - COX-3

 

(COX-3 an alternatively spliced form of COX-1)

Term

 

What is the substrate for COX-1 and COX-2?

Definition

 

arachidonic acid

 

- oxidative cyclization of arachidonic acid by COX enzymes yields PGH2

Term

 

What side effect of NSAIDS were COX-2 inhibitors designed to avoid?

Definition

 

upset stomach, ulcers, GI problems

(prostaglandins normally inhibit GI acid secretion)

Term
What is the rate-limiting enzyme of Fatty Acid synthesis?
Definition

ACC

(Acetyl CoA Carboxylase)

 

- catalyzes the formation of Malonyl CoA from Acetyl CoA

-occurs in cytosol

Term
What are the factors required for the rate-limiting step of Fatty acid synthesis?
Definition

Substrate - Acetyl CoA

Enzyme - ACC (+ citrate for activation)

Energy Requirements - 1 ATP

Coenzyme - Biotin

CO2 for carboxylation of Acetyl CoA

 

Term

In the presence of ____ ACC is phosphorylated, and thereby _______.

 

In the presence of ______ ACC is dephosphorylated, and thereby ______.

Definition

In the presence of Epinephrine ACC is phosphorylated, and thereby inactivated.

 

In the presence of Insulin ACC is dephosphorylated, and thereby activated.

 

- so high insulin stimulated fa synthesis!

Term
What products of fatty acid synthesis act as negative feedback inhibitors?
Definition

 

malonyl CoA (product of regulated step)

 

palmitoyl CoA (16:0) (end-product)

Term

What is the primary source of acetyl CoA used in fatty acid synthesis?

of NADPH?

Definition

acetyl CoA from the pyruvate formed in glycolysis

 

NADPH from hexose monophosphate shunt

-also comes from conversion of malate to pyruvate in cytosol

Term

 

What are two important features that distinguish prostaglandins from hormones?

Definition
Unlike hormones, prostaglandins act locally and are produced by almost all tissues.
Term

What is the commited step of purine de novo biosynthesis?

 

How is it regulated?

Definition

the synthesis of 5'-phosphoribosylamine from PRPP and glutamine

(via glutamine:phosphoribsyl pyrophosphate amidotransferase)

 

this step is inhibited by end-products AMP, GMP, and IMP

Term

True or False:

 

AMP is the precursor for IMP and GMP.

Definition

False -  IMP is the precursor for AMP and GMP.

 

- If both AMP and GMP are present in adequate amounts, the de novo pathway of purine synthesis is turned off at the amidotransferase.

- Synthesis of AMP requires GTP, whereas synthesis of GMP requires ATP

Term

Which of the following amino acids is not used in purine de novo biosynthesis?

A. glutamine

B. cysteine

C. glycine

D. Aspartate

Which are also required for pyrimidine synthesis?

Definition

B. Cysteine

 

- Glycine contributes 2Cs and 1N to purine ring

- Asparatate contributes 1N

- Glutamine contributes 2N

 

- Glutamine and aspartate used in pyr. synthesis

Term

Mycophenolic Acid is a reversible inhibitor of what step in GMP formation?

 

How is it used pharmacologically?

Definition

 

Reversibly inhibits the conversion of IMP to Xanthosine monophosphate by

IMP dehydrogenase

- used to prevent graft rejection by depriving  proliferating T and B cells of nucleic acid components

Term

 

What is the N source in the conversion of hypoxanthine to Adenine?

 

What is the N source in the conversion of xanthine to Guanine?

Definition

Hypoxanthine + Aspartate --> Adenine

 

Xanthine + Glutamine --> Guanine

Term
What are the purine base forms of inosine, guanosine, and adenosine, respectively?
Definition

inosine - hypoxanthine

guanosine - guanine

adenosine - adenine

 

- purine bases lack the (deoxy)ribose sugar and Phosphates of nucleotides

- nucleosides lack the phosphates

Term
What happens in the salvage pathway for purines?
Definition

 

- Adenine is converted to AMP by Adenine phosphoribosyltransferase (APRT)

- Guanine is converted to GMP by Hypoxanthine-guanine phosphoribosyltransferase (HGPRT)

- both use PRPP as the source of the ribose 5-phosphate group

Term
Negative regulation of what enzymes by IMP, AMP, and GMP is lost in Gout?
Definition

Negative regulation of PRPP synthetase (1st step in purine de novo synthesis)

and PRPP amidotransferase (2nd commited step)

 

- results in overproduction of PRPP --> purines

--> urate = buildup of uric acid crystals in joints and hyperuricemia

Term
Allopurinol is used to treat gout by inhibiting what enzyme of purine degradation?
Definition

- Allopurinol inhibits Xanthine oxidase - the enzyme that converts hypoxanthine into xanthine and also xanthine into uric acid.

 

- Accumulation of upstream products xanthine and hypoxanthine is ok b/c they are more soluble than uric acid.

Term
SCID is caused by a deficiency in which purine degradation enzyme?
Definition

ADA  (Adenosine deaminase)

 

- normally converts Adenosine to Inosine

- deficiency leads to buildup of dATP, an inhibitor of ribonucleotide reductase, and therefore of DNA synthesis

- disfunctional T and B cells

Term
Someone with a complete deficiency of HGPRT has lost the ability to salvage hypoxanthine and guanine. What disease do they have?
Definition

Lesch-Nyhan syndrome

 

- In addition to hyperuricemia, symptoms include self-mutilation and mental retardation

Term

 

What step in pyrimidine synthesis is catalyzed by CPS II?

 

Where in the cell does it take place?

Definition

The synthesis of carbamoyl phosphate from glutamine and CO2. Occurs in cytosol.

 

- first step

- committed step

- inhibited by UTP

- activated by ATP and PRPP

Term

What are the 3 classes of RNA polymerases?

 

What does each synthesize?

 

Which one is especially sensitive to a-amanitin?

Definition

RNA polymerase I - rRNAs

RNA polymerase II - mRNAs

RNA polymerase III - tRNAs (& other small RNAs)

 

RNA polymerase II is extremely sensitive to inhibition by a-amanitin

Term
____ are excised and _____ are ligated in the processing of which form of RNA?
Definition

Introns are excised and exons are ligated in the processing of eukaryotic mRNA.

 

(Intervening introns)

(Expressed exons)

Term

Which is not associated with eukaryotic mRNA?

 

A. 3' poly A tail

B. ligation of exons

C. 5'-7-methyl guanosine "cap"

D. polycistronic

 

Definition

D. polycistronic

 

- describes the feature of prokaryotic mRNA that allows a single strand to code for multiple proteins

Term
Which subunit of prokaryotic RNA polymerase finds the starting point for transcription?
Definition
the sigma (s) subunit
Term

What type of RNA makes up the highest percentage of total cellular RNA?

 

The lowest?

Definition

rRNA (ribosomal) is the highest at 80%

 

U1-U6 (small RNAs) are the smallest at <1%

Term

Which DNA polymerase elongates the RNA primer on the lagging strand?

 

Which DNA polymerase excises the RNA primers?

Definition

DNA polymerase III :

- 5' --> 3' polymerase activity for synthesizing DNA, thereby elongating RNA primer

- 3'-->5' exonuclease activity "proofreads" DNA

DNA polymerase I:

- 5' --> 3" exonuclease activity that removes RNA primer and fills the gap (FEN-1 in eukaryotes)

 

 

Term

 Multiple origins of replication is characteristic of

 

A. Eukaryotic DNA replication

B. Prokaryotic DNA replication

C. neither

D. both

 

 

Definition

 

A. Eukaryotic DNA replication

Term
ddl, araC, araA, and AZT all inhibit DNA chain elongation through modification of what part of the chain?
Definition
the sugar moiety of the nucleotide
Term

List the functions of the following Eukaryotic DNA polymerases:

a

b

g

d

e

Definition

a - repair and replication and primase function

b - repair

g - mitochondiral DNA polymerase

d - replication with PCNA (sliding clamp or processivity factor)

e - replication

Term
TTAGGG/CCCTAA are complements comprising what structure?
Definition
telomere
Term
What 3 amino acids act as neurotransmitters?
Definition

glutamate

aspartate

glycine

Term
a-ketoglutarate and oxaloacetate accept  a-amino groups to form what transamination products?
Definition

a-ketoglutarate --> Glutamate

 

oxaloacetate --> Aspartate

Term

 

The first step in the catabolism of all amino acids involves the removal of the _____.

Definition

 

a-amino group

Term
What are the 2 sources of urea Nitrogen?
Definition
Aspartate and Ammonia each provide 1 N
Term
After it is released from glutamate via GDH, NH4+ is incorporated into ____  before entering the urea cycle.
Definition

carbamoyl phosphate

 

-combined with HCO3- by CPS1 in the mitochondria of the liver

Term
All amino acids except ___ and ___ participate in transamination at some point in their catabolism.
Definition
lysine and threonine
Term

Which enzyme of the urea cycle is the regulatory enzyme?

What is its required allosteric activator?

Definition

CPS-1

- catalyzes the first step

- fixes NH4+ as carbamoyl phosphate

- requires N-acetylglutamate

 

Term

What are the 5 enzymes of the urea cycle, in order?

 

Which are found in the mitochondria?

Definition

mitochondria:

CPS-1

Ornithine transcarbamylase

cytosol:

Arginosuccinate synthase

Arginosuccinate lyase

Arginase

 

Term
Arginine is broken down into what 2 products by Arginase?
Definition
Urea and Ornithine
Term

Hyperammonemia affects what part of the body the most?

 

Is caused by a buildup of what?

 

What diseases can cause hyperammonemia?

Definition

- CNS most severely affected

 

- caused by buildup of glutamine

 

- associated with liver failure, HI/HA syndrome (gain of function mutation in GLUD-1), and mutations in any of 5 urea cycle enzymes

Term
Inhibitory regulation of what enzyme is lost in HI/HA?
Definition

GDH

Glutamate Dehydrogenase

 

-gain of function leads to overproduction of ammonia (& insulin)

Term

 

What reaction does Glutamate Dehydrogenase catalyze?

Definition

glutamate --> NH3 + alpha-ketoglutarate

- glutamate the only aa to undergo oxidative deamination by GDH--> releases free NH3

- can use either NAD+ or NADP+ as coenzyme

Term

How many carbons in cholesterol?

progesterone?

testosterone?

estradiol?

Definition

Cholesterol- C27

progesterone - C21

testosterone - C19

estradiol - C18

Term
Which hydroxylases are required in the conversion of progesterone to cortisol?
Definition
17, 21, 11 hydroxylases
Term
Which hydroxylase do Testosterone and Estradiol synthesis both require?
Definition

 

17 hydroxylase

Term

 

Which corticosteroid has an aldehyde at C18?

Definition

 

Aldosterone

 

-acts on kidney to promote Na+ retention and

K+ loss

 

Term

Which is not a characteristic of steroid hormones?

A. act within hours

B. derived from cholesterol (~300mw)

C. affect cAMP levels

D. nuclear receptors

Definition

 

C. affect cAMP levels

 

-in general they do not

- Peptide hormones do!

Term

 

NGF (neurotrophic growth factor) is a "classic" example of what type of hormone signaling?

Definition
paracrine
Term
What is the Fatty acid synthase (FAS) complex made up of?
Definition

 

a dimer made up of two monomers that each have 7 different enzymatic activities plus an acyl carrier protein (ACP) domain.

Term
The first step in Triacylglycerol (triglyceride) synthesis involves the transfer of fatty acyl CoA to what substrate?
Definition

glycerol 3-phospate

 

--> yields a phosphatidic acid

Term
What is phosphatidic acid?
Definition

diacylglycerol with a phosphate group on the 3rd Carbon

 

-forms the base for phosphatidyl compounds

Term

Where does triacylglycerol (triglyceride) synthesis mainly take place?

 

Phospholipid synthesis?

Definition

Triglyceride - mainly synthesized in liver

phospholipid - synthesized in all cells except mature RBCs

Term
What disease is characterized by the accumulation of sphingolipids?
Definition
Niemann-Pick disease
Term
What reaction allows for the "measurement" of blood glucose by dextrostrip reagent strips?
Definition

Paper contains glucose oxidase enzyme.

Glucose + O2 àglucose oxidase à gluconic acid + H202

H202 + ortho-toluidine àperoxidaseà oxidized orthotoluidine (color)

Specific for beta D glucose

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