MCAT Biology 2012

Enzymes are protein _____ that seed up the rate of the reaction by lowering the ____. Enzymes are neither consumed or changed and do not have any effect on the ΔG nor the _____. Most enzyme reactions are _____.

Enzymes are specific: The molecule upon which an enzyme acts is called the _____. Each enzyme has an ____ site upon which the substrate binds, forming the enzyme-substrate complex.

2 models describe formation of enzyme-substrate complex:

1. Lock and Key Theory: Active site is exactly _____ to the spatial structure of its substrate (key)

2. Induced fit: Active site has _____ of shape. When the appropriate substrate and active site come into contact this induces a _____ change.

Cofactors are non-protein molecules that enable ____ activity in enzymes. They either aid in binding the enzyme to the substrate or stabilizing an enzyme in an ____ conformation.

An apoenzyme is an enzyme that is catalytically ____, thus it is devoid of a co-factor. A haloenzyme is catalytically ____, thus it is covalently or non-covalently bound to an enzyme. Tightly bound cofactors are called _____ groups.

A coenzyme is an ____ cofactor, not synthesized by the body but is obtained as ______ derivatives. If these vitamins are not consumed it ____ the corresponding enzyme and can lead to disease.

The rate of a catalyzed reaction depends on concentration, _____, and pH.
Concentration
At low [S] the reaction rate is ____ because most of the active sites of the enzyme are unoccupied. Increasing the [S] leads to proportional or ____ increase in the rate. Once most of the active sites on the enzyme are occupied, the rate levels off at ____.

Michaelis constant (K_m) is the substrate concentration at which the reaction velocity is ____ its maximum. This signifies that ____ of the enzyme's active sites are occupied.
When the reaction rate = 1/2 V_max (graph), K_m = [S]; half of the enzymes active sites are occupied. When the [S]< K_m changes in the [S] greatly affect the ____ of the reaction, there is also ____ affinity of the enzyme for the substrate. When [S]>K_m , V approaches V_max and there is ____ affinity of the enzyme for the substrate.

Regulation of Enzyme Activity: Allosteric Regulation Allosteric Regulation involves the binding of molecules to particular sites on on an enzyme that are _____ from he active site.
An allosteric enzyme has at least one active/catalytic site and one ____ site, thus, it oscillates between an active and inactive conformation.

A regulator molecule can bind to an enzyme and can ____ either the active or inactive configuration of the enzyme. This molecule is different from the substrate.

Enzymatic Activity Interference
Enzyme inhibitors reduce the ____ of the enzyme for its substrate. A decrease in affinity shifts the enzyme kinetics curve to the ____.
Feedback Inhibition: The end product of a sequence becomes an allosteric _____ of one of the preceding enzymes in a sequence. When the end product binds to the allosteric site, the enzyme undergoes a ____ change and can no longer react with its substrate. This allows for organisms to avoid _____ of metabolites.

Competitive Inhibition: A molecule similar to the substrate ____ with the substrate for the active site on the enzyme. If it binds to the enzyme's active site it ____ the enzyme. This process is ____/can be overcome by increasing the concentration of the substrate. Competitive inhibitors reduce V but have no effect on ____. Competitive inhibitors ____ K_m.

Noncompetitive inhibitors bind at an ____ site, not an active site and cannot be displaced by an increase in ____. Noncompetitive inhibitors ____ V_max, but have no effect on K_m.

Cellular metabolism is the ____ of all chemical reactions taking place in a cell. These reactions can either be energy requiring, ivolving the biosynthesis of ____ compounds into smaller molecules~ ____ process; or they can be processes that release energy as they ____ _____ complex organic molecules into smaller molecules~ _____ process. These reactions are ususally coupled so that _____ reactions can fuel _____ reactions.

Photosynthesis is an _____ reaction, also referred to as glucose ______. The net reaction is :
6CO₂ + 6H₂O + energy ----> C₆H₁₂O₆ + O₂

Glycolysis is also called glucose catabolism or _____. The net equation is the reversal of photosynthesis:
C₆H₁₂O₆ + O₂ ------->6CO₂ + 6H₂O + energy

ATP is the cell's main ____ currency. It is synthesized during _____. The molecule is made of the nitrogenous base _____, a ribose sugar and three phoshate groups. The energy is stored in the covalent bonds linking the phosphates.

High potential electrons are removed during _____ and accepted by the coenzymes NAD⁺, ______ and NADP⁺. The high energy electrons are transferred as _____ ions and transported to carrier molecules on the inner _____ membrane also known as the electron ____ chain.

NAD⁺, NADP⁺, and FAD are _____ agents because they cause other molecules to _____ their electrons resulting in their _____ to NADH, NADPH, and FADH₂. This is a ____ process. These coenzymes then behave as _____ agents by transferring their electrons to another acceptor (the first carrier in the _____ _____ _____) resulting in their oxidation (anabolic process).

Glucose Catabolism:

The degradative oxidation of glucose occurs in two stages: glycolysis and cellular _____.

1. Glycolysis occurs in the ____ and leads to the oxidative break down of glucose into 2 _____, the production of ____ and the reduction of NAD⁺ to NADH. The 2 ATP produced during glycolysis are via _____-level phosporylation, which is the production of ATP without the participation of an intermediate such as NAD⁺.The net reaction for glycolyisis:
Glucose + 2ADP + 2p_i + 2 NAD⁺-----> 2 Pyruvate + 2 ATP + 2 NADH + 2 H⁺ + 2 H₂O.

2. Cellular Respiration
a.) Anaerobic- For glycolysis to continue in the absence of oxygen, _____ must be produced. Pyruvate is reduced into either ethanol or _____ acid which produces 2 ATP.
b.) Aerobic
-Pyruvate Decarboxylation: The 2 pyruvate produced from glycolysis are transported into the _____ matrix from the cytoplasm. There they are decarboxylated forming ____-CoA. During the formation of acetyl-CoA CO₂ is produced and NADH is formed.
-Cirtic Acid Cycle: Next the acetyl protion of acetyl-CoA combines with ____(4carbon) forming citrate (6-carbon) and relinquishes CoA (carrier molecule). During the cycle 2 CO₂ are released and oxaloacetate is _____ for another turn in the cycle. *Because there are 2 pyruvate molecules produced during glycolysis the Kreb's cycle must complete ____ circuits/turns to completely break down the pyruvate molecules.* For each turn 1 ATP is produced, 2 CO₂, 3 NADH and 1 FADH, thus for one cycle ___ ATP are produced, ___ CO₂, ___ NADH and ____ FADH.

In the mitochondria high energy electrons are transferred from NADH and ____ to carrier proteins (large protein complexes. The electrons move from cytochrome to cytochrome through the ____ . Each carrier is _____ as it accepts the electrons and then ____ when it passes them to the next carrier. The last carrier is cytochrome a₃ and the final electron acceptor is ____ ---when it accepts the electrons _____ is formed as a byproduct.

Energy loss occurs as electrons are transferred from one complex to the next: electrons from NADH travel through all three complexes, thus ____ ATPs are produced per NADH molecule. Electrons fom FADH₂ bypass the first complex, thus ___ ATP are produced per molecule. This type of ATP production must be coupled to the phosphorylation of ADP and is termed ____ phosphorylation. The coupling of these two processes are called a proton ____. As NADH passes its electrons to the ETC free H⁺ ions (protons) are released and carried across the membrane. These protons accumulate in the _____ space at each complex resulting in the environment eventually becoming acidic and the ____ ____ force drives H⁺ back across the membrane through the ____-synthase carrier. The movement of the protons derive enough energy to allow _____ of ADP to form ATP (oxidative phosphorylation).

Alternate energy sources are used when ____ is low. These alternate sources are converted to glucose or other glucose intermediate and degraded in the ____ pathway or TCA cycle. 1. Carbohydrates are ____ into monosaccharides which are then converted into glucose intermediates that enter glycolysis and the ____ cycle. 2. Fats yield the greatest number of ____ per gram which makes them extremely efficient energy ____ molecules. 3. Proteins

Molecular Biology DNA Structure DNA is the fundamental unit of ____ in cells. DNA and RNA are polymers made of nucleotide monomers. A nucleotide contains ____ groups, a sugar (either ribose for RNA or deoxyribose for DNA), and a ____ base. The nitrogenous base is either a purine (____ or____) or a pyrimidine (_____ , _____ or _____). Adenine always pairs with _____ with 2 hydorgen bonds, and cytosine always pairs with ____ via 3 hydrogen bonds. Uracil replaces ____ in RNA and the ribose has an OH group on carbon 2. DNA is supercoiled in _____ and packaged around histone proteins in _____.

Molecular Biology DNA Structure Nucleotides in the DNA chain are covalently linked by _____ bonds between the 3' _____ group of one deoxyribose and the 5' _____ group of the next deoxyribose. DNA is a right handed double helix held togther by hydrogen bonds between bases. The sugar and phosphate form the ____ of the chain. The two chains are bonded together in an _____ orientation (5' end of one chain is bonded with the 3' end of the other).

Molecular BiologyDNA's JobDNA encodes and transmits the genetic information passed down from parents to offspring.
Information contained in DNA is copied into a messenger RNA (mRNA) in a process called _____, which takes place in the nucleus.
The mRNA then travels to the _____ where it encounters the ribosome and other components of protein synthesis.
The ribosome then synthesizes polypeptides according to the DNA's original orders in a process called _______.

Molecular BiologyDNA's job: The Genetic CodeThe command language used by DNA and mRNA to specify the building block of proteins is called the _____ _____. The genetic code is written in three letter words, each of which codes for a particular ____ _____. A nucleic word (3 nucleotide letters) is referred to as a ______.
There are 64 codons, 61 of them specify amino acids, the remaining three are called nonsense or ____ codons. Their function is to notify the ribosome that the protein is _____ and cause it to stop reading the mRNA.

Molecular BiologyGenetic Mutation:Genetic mutation refers to any _____ of the DNA sequence of an organism's genome. Any compound which can cause mutations is called a _____.
Point Mutations are single base pair _____. -Substitution of a pyrimidine for another pyrimidine or a purine for another purine is called a _____. - Substitution of a purine for a pyrimidine or vice versa is called a ____. -Mutations which cause one amino acid to be replaced with a different amino acid are called ____ mutations. -Mutations which cause a stop codon to replace a regular codon are called _____ mutations and the polypeptide will be truncated as a result. -Mutations which change a codon into a new codon for the same amino acid (no change in amino acid sequence) are called _____ codons.
Insertion mutations refer to the _____ of one or more extra nucleotides.Deletion mutations refer to the ____ of nucleotides from the sequence.
Both insertion and deletion mutations can cause a shift in the reading frame (frameshift mutations).