Biochemistry chapter 11

Question 1

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Answer 1

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Question 3

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What does Dietary fat mostly consist of ? What are the remainder components of it ?

Answer 3

• it contains mainly triacylglycerols

1. * Cholestrol,
2. cholestrol esters,
3. phospholipids, and
4. free fatty acids

Question 4

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Where is the lipid minimal digestion ? Where is it transported to ? What is emulsification ?

Answer 4

• The mouth and the stomach
• * Small intestine *
• Mixing of two normally immiscible liquids( in this case fat and water ) which happens in the duodenum

Question 5

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What aids emulsification ? What does the pancreas secrete ?

Answer 5

Aided by bile which contains bile salts, pigments, cholestrol also its secreted by the liver and stored in the gallbladder It secretes pancreatic lipase, colipase, and cholestrol esterase into the small intestine

Question 6

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What are micelles ? How do they form ?

Answer 6

• Clusters of amphipathic lipids that are soluble in the aqueous environment of the intestinal lumen.
• * Free fatty acids, cholestrol, 2-monoglycerol, and bile salts contribute to the formation

Question 7

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When lipids leave the stomach, what stages of digestion have been accomplished? What enzymes are added to accomplish the next phase ?

Answer 7

Physical digestion is accomplished in the mouth and the stomach, reducing the particle size. Beginning in the small intestine, pancreatic lipase, colipase, cholestrol esterase, and bile assist in the chemical digestion of lipids. In the more distal(away from the origin) portion of the small intestine, absorption occurs

Question 8

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Describe the structure of a micelle ?

Answer 8

Micelles are collections of lipids with their hydrophobic ends oriented toward the center and their charged ends oriented toward the aqueous environment. Micelles collect their lipids within their hydrophobic centers.

Question 9

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What is a chylomicron ?

Answer 9

A microscopic particle of triglycerides produced in the intestines during digestion, in the bloodstream they release their fatty acids into the blood

Question 10

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What is hormone-sensitive lipase ?

Answer 10

Hydrolyzes triacylglycerol yielding fatty acids and glycerol. This happens when there is a fall in insulin level which activates that.

** But usually human adipose tissue doesn’t respond to glucagon

Question 11

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What is lipoprotein lipase necesary for ? What is lipoprotein lipase (LPL) ? What exactly is a lipoprotein ?

Answer 11

• Necessary for metabolism of chylomicrons and very low density lipoproteins(VLDL)

* An enzyme that can release free fatty acids from triacylglycerols in these lipoproteins

* A transport mechanism for lipids within the circulatory and lymphatic systems; include cholymicron and VLDL, which transport triacylglycerol : and HDL and IDL also LDL, which transport cholestrol and cholestrol esters.

Question 12

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What are chylomicrons most soluble in ?

Answer 12

Highly soluble in both lymphatic fluid and blood and function in the transport of dietary tracylglycerol, cholestrol, and cholestrol esters to other tissues

Question 13

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What is (HDL) high density lipoprotein ? What exactly is apoliproteins ?

Answer 13

• Synthesized in the liver and intestines and released as dense, protein-rich particles into the blood. HDL contains apolioproteins used for cholestrol recovery-that is the cleaning up excess cholestrol from blood vessels excretion.
• * Proteins molecules responsible for the interaction of lipoproteins with cells and the transfer of lipid molecules between lipoproteins; also called apoproteins
• * the majority of the cholestrol measured in blood is associated with LDL

Question 14

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What is the primary method of transporting free fatty acids in the blood ?

Answer 14

Free fatty acids remain in the blood, bound to the albumin and other carrier proteins. A much smaller amount will remain unbound

Question 15

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Order the lipoproteins from greatest percentage of protein to least percentage of protein. Circle the molecules that are primarily involved in tracylglycerol transport.

Answer 15

With respect to the protein count. HDL>LDL>IDL>VLDL>chylomicrons. VLDL and chylomicrons are the primary triacylglycerols transporters. HDL and LDL are mostly involved in cholestrol transport

Question 16

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Lipoproteins are synthesized primarily by which two organs ?

Answer 16

Synthesized primarily by the intestine and liver

Question 17

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What is cholestrol ?

Answer 17

A ubiqtuous(being present everywhere) component of all cells in the human body and plays a major rule in the synthesis of cell membranes, steroid hormones, bile acids, and vitamin D

Question 18

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what is de novo synthesis and where does it occur ?

Answer 18

• Synthesis of a complex molecule which refers to the biochemical pathway where a complex biomolecule is synthesized new from a simple biomolecule
• * it occurs in the liver and is driven by acetyl-CoA and ATP

Question 19

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What is the citrate shuffle ? Mevalonic acid ?

Answer 19

• it carries mitochondrial acetyl-CoA into the cytoplasm, where synthesis occurs. NADPH( from the pentose phosphate pathway) supplies reducing equivalents. In the synthesis of that, which is in the SER its the rate limiting step in cholestrol biosynthesis and is catalyzed by 3-hydroxy-3-methylglutaryl (HMG) CoA reductase .
• Mevaolnic acid is basically a molecule precursor of many endogenous molecules e.g cholestrol coenzyme, steroids, terpenes

Question 20

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What is Lecithin-cholestrol-acetyltransferase (LCAT) ?

Answer 20

Enzyme found in the bloodstream that is activated by HDL apoproteins. it adds a fatty acid to cholestrol which produces soluble cholestryl esters such as those in HDL.

Question 21

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What conditions is HMG-CoA reducatase most active ? In what cellular region does it exist ?

Answer 21

HMG-CoA is most active in the absence of cholestrol and when stimulated by insulin. Cholestrol reduces the activity of HMG-CoA reductase, which is most likely located in the smooth endoplasmic reticulum

Question 22

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What proteins are specific to the transport and release of cholestrol, and what are their functions ?

Answer 22

LCAT catalyzes the esterification of cholestrol to form cholestrol esters. CETP promotes the transfer of cholestrol esters from HDL to IDL, forming LDL

Question 23

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What is the nontemplate synthesis ?

Answer 23

aka the lipid and carbohydrate synthesis because they dont rely directly on the coding of the nucleic acid, unlike protein and nucleic acid synthesis

Question 24

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Palmitic acid ( palmitate)?

Answer 24

Primary end product of fatty acid synthesis.

Question 25

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what is Acetyl-CoA carboxylase ?

Answer 25

Requires biotin and ATP to function, and adds CO2 to acetyl-CoA to form malonyl-CoA which is activated by insulin and citrate

Question 26

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What is fatty acid synthase ?

Answer 26

A large multienzyme complex found in the cytosol that is rapidly induced in the liver following a meal high in carbohydrates because of elevated insulin levels. Also called palmitate synthesis cause its the only fatty acid that humans can synthesize de novo

Question 27

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What exactly is a-oxidation and b-oxidation ?

Answer 27

Takes place in microsomes in brain and liver, involves decarboxylation proces for the removal of the single carbon atom at one time with resultant production of an odd fatty acid that can be subsequently oxidized by beta oxidation for energy oxidation * Catabolic process by which fatty acids are broken down in the cytosol in prokaryotes and in the mitochondria in eukryotes to generate acetyl-CoA

Question 28

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What are the four steps of B-oxidation ?

Answer 28

1. * Oxidation of fatty acids to form a double bond
2. * Hydration of the double bond to form a hydroxyl group
3. * Oxidation of the hydroxyl group to form a carbonyl (B-ketoacid)
4. Splitting of the B-ketoacid into a shorter acyl-CoA and acetyl-CoA This process continues until the chain has been shortened to two carbons. creating a final acetyl-CoA

Question 29

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What does Enoyl-CoA isomerase do ?

Answer 29

Rearranges cis bonds at the 3,4 position to trans double bonds at the 2,3 position once enough acetyl-CoA has been liberated to isolate the double bond within the first three carbons. {{26 1 0.jpg}}

Question 30

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what exactly is acetoacetic acid ?

Answer 30

its a intermediate in the metabolism of fatty acids in most organisms. In mammals it is also produced in the liver along with other ketone bodies, and is released into the bloodstream as an energy source *its a conjugate base for acetoacetate*

Question 31

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What are the five steps in the addition of acetyl-CoA to a growing fatty acid chain ?

Answer 31

1. the steps in the attachment of acetyl CoA to a fatty acid chain are attachment to acyl carrier protein,
2. bond formation between molecules,
3. reduction of a carboxyl group,
4. dehydration,
5. reduction of a double bond.

Question 32

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How does B-oxidation of unsaturated fatty acids differ from that of saturated fatty acids ?

Answer 32

there is an additional isomerase and an additional reductase for the B-oxidation of unsaturated fatty acids, which provide the stereochemistry necessary for further oxidation. Also it is true that fatty acids are synthesized in the cytoplasm and modified by enzymes in the smooth endoplasmic reticulum

Question 33

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What happens with ketone bodies acetoacetate and 3-hydroxybutate(B-hydroxybutrate) ?

Answer 33

In the fasting state, the liver converts excess acetyl-CoA from B-oxidation of fatty acids into those enzymes which are used energy in various tissues.

Question 34

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What exactly is ketogenesis and ketolysis ?

Answer 34

The formation of ketone bodies in the liver mitochondria which is composed of acetoacetic acid, B-hydroxybutyric acid, and acetone

* Complete oxidation of ketone bodies to CO2 and water, occurs in the extrahepatic tissues due to high activity of the enzymes

Question 35

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Why are fatty acids used to create ketone bodies instead of creating glucose ?

Answer 35

Fatty acid degradation results in large amounts of acetyl-CoA, which can’t enter the gluconeogenic pathway to produce glucose. Only odd numbered fatty acids can act as a source of carbon for gluconeogenesis; even then, only the final malonyl-CoA molecule can be used. Energy is packaged into ketone bodies for consumption by the brain and muscles.

Question 36

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What conditions and tissues favor ketogenesis ? ketolysis ?

Answer 36

ketogenesis is favored by a prolonged fast and occurs in the liver. it is stimulated by increasing concentrations of acetyl-CoA. Ketolysis is also favored during a prolonged fast , but is stimulated by a low energy state in muscle and brain tissues and does not occur in the liver.

Question 37

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Do bodily proteins commonly get broken down to provide acetyl-CoA for lipid synthesis ?

Answer 37

Nope. Proteins are more valuble to the cell than lipids, thus they will not commonly be broken down for lipid synthesis

Question 38

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Where does the bulk of the protein digestion occur ?

Answer 38

In the small intestine

Question 39

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During protein processing, what is the eventual fate of

• * Carbon skeleton
• * Amino group
• * Side chains

Answer 39

• * The skeleton is transported to the liver for processing into glucose or ketone bodies
• * Amino group will feed into the urea cycle for excretion
• * Processed depending on their composition. Basic side chains will be processed like amino groups, while other functional groups will be treated like the carbon skeleton

Question 40

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What conditions and hormones promote lipid mobilization from fat stores ? What is the ratio of free fatty acids to glycerol ?

Answer 40

• In the postabsorptive and prolonged fasting states, lipid mobilization is favored. A decrease in insulin levels, as well as increase in epineprine or cortisol will increase lipid mobilization from adipocytes.
• * the ratio of free fatty acids to glycerol is 3 : 1 . A glycerol molecule is composed of glycerol and three fatty acids