MCAT BIOCHEM Part 3 Flashcards
The enzymes of the Krebs cycle and the pyruvate dehydrogenase complex are located in the ___
matrix
The enzymes of the electron transport chain and ATP synthase are bound to the __
inner mitochondrial membrane
The two goals of the electron transport or oxidative phosphorylation are to:
- reoxidize all the electron carriers reduced in glycolysis, PDC, and the Krebs cycle
- Store energy in the form of ATP i nthe process
The ___ is a group of five electron carriers. Each reduces the next member down the line.
Electron transport chain
The first electron carrier in the electron transport chain is ___
NADH dehydrogenase it oxidizes NADH to NAD+
The reason cyanid is a poison is that it inactivates cytochrome C oxidase by binding to its active site with high affinity. When a person is exposed to cyanide what happens?
The electron transport chain ceases to transport electrons and therefore ceases to pump protons
Each molecule of NADH provides the energy to produce approximately ___
2.5 ATP molecules
The ETC must pump ___ protons to produce 1 molecule of ATP
4 protons
FADH2 gives its electrons to ___
ubiquinone
FADH2 pumps ___ protons across the inner membrane
6 protons
FADH2 oxidation to FAD only produces___ ATP
1.5
The electrons of NADH produced in glyoclysis must be transported into the mitochondria before they enter the ETC by a pathway termed the __
glycerol phosphate shuttle
The glycerol phosphate gives electrons from NADH directly to ___
ubiquinone
Cytosolic NADH from glycolysis only produces
1.5 molecules of ATP
Krebs cycle produces ___,___,and ___
6 NADH
2 FADH2
2 GTP
The Pyruvate Dehydrogenase Complex produces ___
2 NADH
The total number of ATP for cellular respiration is
30 ATP
In energy-starved states ___ levels activate PFK while inhibiting F-1,6-BPase, resulting in enhanced glycolsysi activity and a suppression of gluconeogenesis
AMP
Skeletal muscle lacks glucose-6-phosphatase the absence of this enzyme__
keeps glucose phosphorylated and unable to leave the muscle cell
The enzyme ____ is required to transport glucose in the bloodstream
Glucose-6-phosphatase
___ are composed of long unsubstituted alkanes that end in a carboxylic acid
Fatty acids
____ are typically 14-18 carbons long and synthesized two carbons at a time from acetate, thus in humans ___ are even numbered predominantly
Fatty acids
___ have one or more double bond in the tail and they are almost always (cis) or (Z)
Unsaturated fatty acids
Triglyceride is composed of ____
three fatty acids esterified to a glycerol molecule
Glycerol is a three-carbon triol
Soaps are formed by base-catalyzed hydrolysis of triglycerides from animal fat into fatty acid salts, reaction called__
saponification
What are the two reasons fats are more efficient energy storage molecules than carbohydrates?
- Packing
2. Energy content
Describe the packing that makes fats more efficient than carbohydrates.
Hydrophobicity of fats allow them to pack together closer than carbohydrates.
Carbohydrates carry a great amount of water-of-solvation (water molecules hydrogen bonded to their hydroxyl groups)
Amount of carbon per unit area or unit weight is much greater in a fat droplet than in dissolved sugar
Describe why a fat has more energy content than a carbohydrate
A fat is much more reduced than a carbohydrate. Energy metabolism begins with the oxidation of foodstuffs to release energy. Since carbohydrates are more oxidized to begin with, oxidizing them reelases LESS energy
__ and ___ are the most common phospholipids in the eukaryotic cell
Phosphatidylcholine and phosphatidylethanolamine
___ is a major lipid component of lung surfactant (important in reducing surface tension inside lung alveoli)
Phosphatidylcholine
___drive formation of the bilayer
___ stabilized the bilayer
Hydrophobic interactions drive the bilayer, van Der Waals forces stabilize the bilayer
Phospholipids composed of saturated fatty acids make the lipid membrane__
LESS fluid
double bonds in phospholipid fatty acids tends to__
INCREASE membrane fluidity,
also decreasing the length of fatty acids increase fluidity
___ is known as membrane antifreeze because at low temperatures, it increases the fluidity in the same way as kinks in fatty acid tails do
Cholesterol
At high temperatures__ REDUCES membrane fluidity
Cholesterol
The three structural determinants of membrane fluidity are
- Degree of saturation
- Tail length
- Amount of cholesterol
A ___ is a member of a broad class of compounds built from isoprene units (C5H8)
Terpene
___ exert their effects by binding to receptors at the cell-surface
Peptide hormones
___ diffuse into the cell where their receptors are located
Steroid hormones
___ is an important component of the myelin sheath around neurons,
Sphingomyelin (a type of sphingolipid)
The four fat-soluble vitamins are
A,D,E, and K all ring structured
___ is a terpenoid essential for vision, growth, epithelial maintenance, and immune function
Vitamin A
___ is derived from cholesterol important in regulating blood levels of calcium and phosphate
Vitamin D
__ is actually a group of compounds called tocopherols (methylated phenols) that are important as antioxidants
Vitamin E
__ serves as an important coenzyme in the activation of clotting proteins
Vitamin K
Fatty acid catabolism occurs in the __
mitochondrial matrix
Fatty acid anabolism takes place in the
Cytoplasm
What are the pKa for the three acid dissociation equilibria of phosphoric acid?
2.1, 7.2, 12.4
ATP synthesis is driven by __
protons crossing the inner mitochondrial membrane through ATP synthase
Fermentation is the reduction of ____
Pyruvate to lactate to generate NAD+ for continued glycolysis under aerobic conditions
Citric acid cycle converts citrate to oxaloacetate through several intermediates including ___ ,__,__, and__
a-ketoglutarate, succinate, fumarate, and malate
Firs step of glycogenolysis is__
glucose-1 phosphate is made and converted to glucose-6-phosphate through the enzyme phosphoglucomutase
Degradation of glycogen occurs with process of _____
phosphorolysis which removes individual glucose sub units
The first step of glycogen where glucose subunits are removed is catalyzed by __
glycogen phosphorylase
What does the enzyme glycogen phosphorylase do?
Glycogen phosphorylase breaks a,1-4 bond by adding inorganic phosphate at carbon 1, Glucose-1-phosphate (G1P) released
___ breaks bonds by adding inorganic phosphate groups across them
Phosphorolysis
Glycolysis produces ___ ATP per glucose
2 ATP
Gluconeogenesis consumes total of __ ATP equivalents
6 ATP
The rate of glycolysis is largely controlled by ___
PFK-1 activity.
-When PFK-1 is active, glycolysis proceeds quickly
PFK-1 is tightly regulated by several allosteric inhibitors and activators including
Allosteric inhibitors : ATP and citrate
Allosteric activators: ADP, AMP, and F2,6BP
___decreases the rate of glycolysis and increases the rate of gluconeogenesis
Glucagon
___reactions join two molecules together and release one or more water molecules in the process
Condensation rxn
How does insulin stimulate glucose catabolism?
Glucose catabolism (glycolysis) by activating synthesis of fructose-2,6-bisphosphate (F2,6BP). F2,6BP allosterically ACTIVATES phosphofructokinase-1 (PFK-1) which catalyzes the rate limiting step of glycolysis
-In the liver F2,6BP inhibits fructose-1,6 bisphosphatase, which catalyzes the dephsphorylation of F1,6BP in gluconeogenesis
The rate limiting step of glycolysis is ___
Phosphofructokinase-1 catalyzed
What is the rate limiting step of Pentose phosphate pathway?
The conversion of Glucose-6-Phosphate to 6-Phosphogluconate by
Glucose-6 phosphate dehydrogenase
What two enzymes in the Pentose phosphate pathway catalyze and produce NADPH?
Glucose-6-phosphate dehydrogenase
6-phosphogluconate dehydrogenase
What are the three enzymes that are allosterically regulated in the Krebs cycle because they are irreversible?
Citrate synthase
Isocitrate dehydrogenase
a-ketoglutarate dehydrogenase
The allosteric inhibitors of the three irreversible steps of the Krebs cycle are
NADH, ATP, Citrate, and succinyl-CoA
The allosteric activators of the three irreversible steps of the Krebs cycle are _
ADP and Calcium
What is the regulatory step enzyme for glycolysis?
What are positive regulators?
What are negative regulators?
Regulatory step enzyme of glycolysis: Phosphofructokinase
Positive Regulators: Fructose-2,6-bisphosphate, AMP
Negative regulators: ATP
What is the regulatory step enzyme for gluconeogenesis?
What are positive regulators?
What are negative regulators?
Regulatory enzyme of gluconeogenesis: Fructose-1,6-bisphosphatase
Positive regulators: ATP
Negative Regulators: Fructose-2,6-bisphosphate, AMP
Insulin stimulates both ___ and __
Glycolysis and Glycogenesis
__ occurs in response to glucagon when blood sugar levels are low. Results in glucose being released from the liver into the blood where it can be uptaken by the cells and enter glycolysis
Glycogenolysis
All amino acids are derived from __
L-glyceraldehyde
The simplest (smallest) carbohydrate has only three carbons and one chiral center it is called__
glyceraldehyde
All animal carbohydrates are chemically derived from __
D-glyceraldehyde
