MCAT: Biochemistry and Biology

Biochemistry and biology topics tested on the mcat.

Michaelis constant (Low, High)

Km represents the substrate concentration at half Vmax, a ___ Km indicates high substrate affinity, while a __ Km indicates low substrate affinity

Competitive Inhibition

Inhibitor binds to the active site (free enzyme only), increasing Km while leaving Vmax unchanged, high substrate concentrations can outcompete the inhibitor

Noncompetitive Inhibition

Inhibitor binds to an allosteric site with equal preference for free enzyme and ES complex, decreasing Vmax while leaving Km unchanged. Since a portion of the enzyme population is functionally inactivated the active enzyme capacity drops, decreasing Vmax​. However, because the inhibitor does not block site's ability to bind substrate, the enzyme's substrate affinity is unchanged, leaving Km​ constant.

Uncompetitive Inhibition

Inhibitor binds only to the allosteric site of the ES complex, decreasing both Km and Vmax by the same ratio by trapping substrate in the active site. By trapping substrate in the ESI complex, they deplete active ES to lower Vmax​, while simultaneously shifting the E+S⇌ES equilibrium to the right, which lowers Km​ by the exact same ratio.

Mixed Inhibition

Inhibitor binds allosterically with unequal preference for free enzyme vs. ES complex, always decreasing Vmax while increasing Km (if preferring free enzyme) or decreasing Km (if preferring ES complex)

Transcription Factor

A specialized regulatory protein that enters the nucleus, binds directly to specific DNA sequences (promoters or enhancers), and acts as a molecular switch to recruit or block RNA polymerase

Embryonic Germ Layers (Endo, Meso, Ecto)

The ___derm forms internal linings (GI tract, liver, pancreas), the __derm forms structural and circulatory systems (muscle, bone, heart, blood), and the _derm forms nervous tissue and epidermis

Endoderm

The innermost germ layer that creates the lining of the digestive tract, lungs, liver, and pancreas. For instance, Hepatocytes (liver) and Pancreatic (pancreas) Beta Cells

Monocyte

This cell type is a circulating leukocyte that differentiates in body tissues into a macrophage, a phagocytic immune cell that engulfs cellular debris, pathogens, and lipids

Foam Cell

A lipid-laden macrophage formed when a macrophage ingests excessive amounts of oxidized LDL in an arterial wall, contributing to atherosclerotic plaque

Leukocyte Definition

The general term for any white blood cell involved in immune defense, including lymphocytes (T and B cells), granulocytes (neutrophils, basophils, eosinophils), and monocytes

Lactic Acid Fermentation

Uses NADH to reduce pyruvate into lactate under anaerobic conditions, regenerating NAD+ to sustain glycolysis

Genetic Linkage and Recombination Frequency

Linked loci reside on the same chromosome and have a recombination frequency of less than 50%, unlinked genes exhibit a maximum recombination frequency of 50%

Krebs Cycle Intermediates

Citrate, Isocitrate, Alpha-Ketoglutarate, Succinyl-CoA, Succinate, Fumarate, Malate, Oxaloacetate (Can I keep Selling S** For Money Officer?)

Ovulation

Driven by a peak in estrogen that triggers a massive surge of Luteinizing Hormone (LH) from the anterior pituitary gland around day 14 of the menstrual cycle

Corpus Luteum

Formed from the ruptured follicle post-ovulation, it secretes high levels of progesterone (and some estrogen) to thicken and maintain the endometrium

Ovarian Cycle Phases (Follicular, Ovulation, Luteal)

During the first phase, FSH drives follicle growth and estrogen production; during the second phase, an LH surge releases the egg; and during the third phase, the corpus luteum secretes progesterone;

Alpha vs. Beta Anomers

Determined by the C1 anomeric carbon hydroxyl group in D-sugars, if the -OH points down (opposite the C5 tail), it is the alpha-anomer, if it points up (same side as the tail), it is the beta-anomer

D vs. L Sugar

Determined by the highest-numbered chiral center (C5 in hexoses), if the -CH2OH tail points up in a Haworth projection, it is a D-sugar, if it points down, it is an L-sugar. In a Fischer projection with the carbonyl carbon at the top, a D-sugar has the hydroxyl (–OH) group on the bottom-most chiral center pointing to the right, while an L-sugar has it pointing to the left

Viral Transduction / Entry

Process where viral genetic material is internalized into the host cell cytoplasm, often utilizing receptor-mediated endocytosis or direct membrane fusion

Crossing Over (Recombination)

Occurs specifically during Prophase I of meiosis, exchanging genetic material between non-sister homologous chromatids to increase genetic diversity

Mitosis vs Meiosis

Mitosis yields two identical diploid (2n) somatic cells in one division, Meiosis yields four genetically distinct haploid (1n) gametes across two divisions

Blotting Techniques (SNoW DRoP) (Southern, Northern, Western)

___ blot detects DNA, __ blot detects RNA, and _ blot detects proteins

mRNA vs. DNA Stop Codons

Stop codons appear in mRNA as UAA, UAG, and UGA, in coding DNA sense strand, they correspond to TAA, TAG, and TGA. The anti sense strand would be reversed and the pairs. TCA, CTA, and TTA

Insulin

Secreted by pancreatic beta cells in response to high blood glucose to promote glucose uptake, glycogenesis, and fatty acid synthesis while lowering blood sugar;

Nonsense Mutation

A point mutation that introduces a premature stop codon into mRNA, resulting in a truncated, nonfunctional protein

Missense Mutation

A point mutation that replaces a single nucleotide, changing one codon so that it codes for a different amino acid

Frameshift Mutation

An insertion or deletion of nucleotides not in multiples of three, shifting the reading frame and altering all downstream amino acids

Silent Mutation

A nucleotide substitution that alters a codon without changing the encoded amino acid due to genetic code degeneracy

Pulmonary Circulation Oxygen (arteries, veins)

Unlike systemic circulation, pulmonary ___ carry deoxygenated blood away from the heart, and pulmonary ___ carry oxygenated blood to the heart

Alkalization Definition

The addition of a base to raise pH (increasing OH- or decreasing H+ concentration)

Gastrointestinal Nutrient Flow

Absorbed nutrients from the small intestine enter the hepatic portal system to travel directly to the liver before reaching systemic circulation

Kinetochore

A protein structure assembled on the centromere that serves as the attachment site for spindle microtubules to pull sister chromatids apart

Chromosome and Cytoskeletal Structures

Centromeres join sister chromatids, centrosomes are microtubule-organizing centers containing centrioles, and asters are radial microtubule arrays extending from centrosomes

Amino Acid Charge at Physiological pH

At pH 7.4, the backbone amino group is protonated (-NH3+) and the carboxyl group is deprotonated (-COO-), forming a zwitterion

Sliding Filament Theory Force Generation

Maximum contractile force in a muscle fiber occurs at an optimal length where there is maximal overlap between thick (myosin) and thin (actin) filaments

Lymphatic Drainage and Blood Volume

Lymphatic vessels collect excess interstitial fluid and return it to the venous bloodstream via the thoracic duct, maintaining blood volume and plasma levels

Membrane Potential Movement

Transmembrane ion movement is electrically favorable when ions move toward the side of the membrane with an excess of opposite charges

Mitochondrial Proton Gradient

Protons are pumped from the matrix into the intermembrane space, creating a higher H+ concentration (lower pH) in the intermembrane space to drive ATP synthase

Erythrocyte Characteristics

Red blood cells lack a nucleus and mitochondria, relying entirely on anaerobic glycolysis for ATP production to prevent consuming the oxygen they transport

Wobble Base pair

Non-standard base pairing occurs between the 1st position of the tRNA anticodon (5' end) and the 3rd position of the mRNA codon (3' end), accommodating genetic code degeneracy

Glycolysis

Occurs in the cytosol to break down glucose into pyruvate, generating a net of 2 ATP and 2 NADH when cellular ATP demand is high;

Gluconeogenesis

Occurs primarily in the liver cytosol and mitochondria during prolonged starvation or low glucose conditions to synthesize new glucose from non-carbohydrate precursors;

Glycogenesis

Occurs in the cytosol of liver and muscle tissue after meals in response to elevated blood glucose and insulin to store excess glucose as glycogen;

Glycogenolysis

Occurs in the cytosol of liver and muscle tissue during fasting or exercise in response to glucagon and epinephrine to break down glycogen into glucose-6-phosphate;

Pentose Phosphate Pathway

Occurs in the cytosol to convert glucose-6-phosphate into NADPH for anabolic reduction reactions and ribose-5-phosphate for nucleotide synthesis;

Citric Acid Cycle

Occurs in the mitochondrial matrix under aerobic conditions to oxidize acetyl-CoA into CO2, generating 3 NADH, 1 FADH2, and 1 GTP per turn for cellular energy production;

Electron Transport Chain

Occurs across the inner mitochondrial membrane under aerobic conditions to oxidize NADH and FADH2, creating a proton gradient that drives mass ATP synthesis via oxidative phosphorylation;

Fermentation

Occurs in the cytosol under anaerobic conditions to reduce pyruvate into lactate or ethanol, regenerating NAD+ to sustain ongoing glycolysis for quick ATP production;

Beta-Oxidation

Occurs in the mitochondrial matrix during fasting or high energy demand to break down fatty acids into acetyl-CoA, NADH, and FADH2;

Fatty Acid Synthesis

Occurs in the cytosol of liver and adipose tissue during energy surplus to build fatty acids from excess acetyl-CoA and NADPH;

Ketogenesis

Occurs in liver mitochondria during extreme starvation or prolonged low carbohydrate intake to convert excess acetyl-CoA into ketone bodies for brain and heart fuel

Glucagon

Secreted by pancreatic alpha cells in response to low blood glucose to stimulate glycogenolysis and gluconeogenesis in the liver to raise blood sugar;

Antidiuretic Hormone

Synthesized in the hypothalamus and released by the posterior pituitary to insert aquaporins into collecting ducts, increasing pure water reabsorption to increase blood pressure and decrease blood osmolarity;

Aldosterone

Secreted by the adrenal cortex to increase Na+ reabsorption and K+/H+ excretion through Na + /K + ATPase in distal tubules in the nephron, increasing blood volume and pressure without changing blood osmolarity;

Calcitonin

Secreted by thyroid parafollicular C cells when blood calcium is high to inhibit osteoclasts and promote renal calcium excretion, lowering blood calcium levels;

Parathyroid Hormone

Secreted by parathyroid glands when blood calcium is low to stimulate osteoclasts, increase intestinal calcium absorption via Vitamin D activation, and decrease renal calcium excretion;

Cortisol

Secreted by the adrenal cortex during long-term stress to increase blood glucose through gluconeogenesis, inhibit protein synthesis, and suppress immune responses;

Epinephrine

Secreted by the adrenal medulla during short-term acute stress to trigger sympathetic fight-or-flight responses, increasing heart rate, glycogenolysis, and blood flow to skeletal muscle;

Growth Hormone

Secreted by the anterior pituitary to stimulate tissue growth, cell division, and muscle protein synthesis while mobilizing fatty acids for energy;

Prolactin

Secreted by the anterior pituitary to promote milk production in mammary glands after childbirth;

Oxytocin

Hormone synthesized in the hypothalamus and released by the pituitary gland. It triggers labor contractions, helps with breastfeeding, and supports social bonding, trust, and romantic attachment

Thyroid Hormones T3 and T4

Secreted by thyroid follicular cells to set baseline metabolic rate, regulate basal oxygen consumption, and drive heat production throughout the body;

Atrial Natriuretic Peptide

Secreted by cardiac atrial cells when blood pressure is high to promote renal Na+ and water excretion, lowering blood volume and system pressure;

NADH and FADH₂ ATP

Each __ yields about 2.5 ATP and each _ yields about 1.5 ATP

NADH Function

Acts as a reducing agent that transfers electrons to reduce target molecules like converting a ketone into a secondary alcohol

Triacylglycerol

Storage lipid composed of three fatty acid chains ester linked to a single glycerol backbone

Adipocyte

Specialized animal cells dedicated to storing fat as triacylglycerols for long term energy reserves

Purines versus Pyrimidines

Purines Adenine and Guanine contain two fused rings while pyrimidines Cytosine Thymine and Uracil contain a single ring

Cysteine versus Methionine

Cysteine contains a reactive (-SH) sulfhydryl group capable of forming covalent disulfide bridges whereas methionine contains a nonreactive thioether (-S-CH₃)

ETC Complex I

NADH dehydrogenase which accepts electrons from NADH and pumps four protons into the intermembrane space

ETC Complex II

Succinate dehydrogenase which accepts electrons from FADH2 and passes them to coenzyme Q without pumping protons

ETC Complex III

Cytochrome bc1 complex which transfers electrons from ubiquinol to cytochrome c while pumping four protons across the inner membrane

ETC Complex IV

Cytochrome c oxidase which transfers electrons from cytochrome c to oxygen to form water while pumping two protons

Phosphofructokinase 1 Regulation

PFK1 is allosterically inhibited by high levels of ATP through negative feedback signaling high cellular energy

Resting Membrane Potential

Maintained by the Sodium Potassium ATPase pumping three sodium ions out for every two potassium ions brought in alongside potassium leak channels allowing positive charge to drift out

Action Potential Phases

Voltage gated sodium channels open causing rapid depolarization until sodium channels close then voltage gated potassium channels open allowing potassium to leave and repolarize the cell back toward resting potential. The membrane potential is restored, but the sodium ion concentrations are flipped. The Na+/K+-ATPase uses active transport (1 ATP molecule) to pump 3 Na+ OUT and 2 K+ IN to the cell (both against their concentration gradient).

Isoelectric Point and Charge

A protein placed in an environment with a pH lower than its pI becomes protonated gaining a net positive charge as basic groups grab extra protons

Nuclear Localization Sequence

Mandatory signal sequence found on cytosolic translated proteins that must enter the nucleus including RNA polymerase transcription factors, DNA repair enzymes, and histones

GAPDH

Step 6 of Glycolysis! Glyceraldehyde 3 phosphate dehydrogenase catalyzes the reversible conversion of G3P into 1 3 bisphosphoglycerate while reducing NAD+ to NADH. (the first energy-yielding step of glycolysis).

Vasopressin

Also called Antidiuretic hormone that triggers the insertion of aquaporins into the collecting duct to increase water reabsorption raising blood pressure and blood volume

Prion

Infectious misfolded proteins that induce normal cellular proteins to misfold into pathological aggregates causing neurodegenerative damage

Estrogen Regulation

Secretion and overall circulating levels of estrogen can be enhanced by Luteinizing Hormone signals from the anterior pituitary

Protease

Enzymes that degrade proteins by cleaving peptide bonds to digest them into smaller fragments

Translation Directionality

Ribosomes read mRNA transcripts in the 5 prime to 3 prime direction while synthesizing proteins from the N terminus to the C terminus

Ectoderm Derivatives

Outer germ layer giving rise to the nervous system epidermis hair nails and epithelial lining of the mouth and anus

Mesoderm Derivatives

Middle germ layer giving rise to muscles bones circulatory system kidneys gonads and dermis

Endoderm

Inner germ layer giving rise to the epithelial lining of the digestive and respiratory tracts liver and pancreas

Actin Microfilaments

Cytoskeletal filaments made of actin that drive intracellular transport cell crawling cytokinesis and structural support

Microtubules

Dynamic hollow tubes composed of alpha and beta tubulin dimers originating from centrosomes that form tracks for intracellular transport and the mitotic spindle

Cytotoxic T Lymphocytes

T cells that recognize specific viral antigens presented on MHC Class I molecules to induce apoptosis in infected host cells

Antibody

Y shaped molecule composed of two heavy and two light chains held by disulfide bonds featuring variable regions for specific antigen binding and constant regions for immune signaling

Epididymis

Structure adjacent to the testes where newly formed sperm mature and gain motility and fertilizing capability

Muscle Contraction

ATP binding to the myosin head causes it to detach from the actin filament allowing muscle relaxation

Reducing Agents in Electrophoresis

Chemical agents like beta mercaptoethanol that reduce and break disulfide bridges connecting protein subunits

Sliding Filament Model

Calcium binds troponin shifting tropomyosin to expose actin sites allowing myosin binding power stroke driven by ADP release and detachment by new ATP binding

Somatic vs Germline Mutations

Mutations are only inherited by progeny if they occur in germline cells so acquired mutations in body tissues that cause cancer are presumed somatic unless stated otherwise

Intron Characteristics

Non-coding RNA regions that are spliced out during processing which lack promoter and coding sequences but contain splice acceptor and donor sites

Signal Sequence

A peptide sequence encoded at the 5 prime end of mRNA that targets newly synthesized proteins to the endomembrane system for membrane insertion or secretion

Chemiosmosis

The mechanical movement of protons down their electrochemical gradient through ATP synthase to phosphorylate ADP to ATP without direct electron transfer or redox reactions