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MCAT Biochemistry Flashcards
51 question-and-answer cards covering Biochemistry as it is examined in MCAT. 24 of them are printed below, taken from across the deck — no signup, no paywall on the preview.
24 sample cards from the Biochemistry deck
Sampled from the end of the deck, so these are different cards from the ones shown on the syllabus page.
Which common disaccharide is a non-reducing sugar, and why?
Sucrose. Its glycosidic bond joins both anomeric carbons (glucose C1 to fructose C2), so neither monosaccharide has a free anomeric carbon to open into a reactive aldehyde/ketone.
Compare the structures of amylose, amylopectin, and glycogen.
Amylose: linear $\alpha(1\to4)$ glucose chains. Amylopectin: $\alpha(1\to4)$ chains with $\alpha(1\to6)$ branches (~every 24-30 residues). Glycogen: like amylopectin but more highly branched (~every 8-12 residues).
What glycosidic bond makes cellulose indigestible to humans, and how does it differ from starch?
Cellulose uses $\beta(1\to4)$ linkages, forming straight, rigid chains that human amylases (which cleave $\alpha(1\to4)$) cannot hydrolyze. Starch uses digestible $\alpha(1\to4)$ bonds.
What are the net products of one round of glycolysis per glucose?
$2$ pyruvate, $2$ ATP (net; $4$ produced $-$ $2$ consumed), and $2$ NADH.
Name the three irreversible, regulated enzymes of glycolysis.
Hexokinase/glucokinase, phosphofructokinase-1 (PFK-1, the main rate-limiting step), and pyruvate kinase.
What is the rate-limiting enzyme of glycolysis and its key allosteric regulators?
Phosphofructokinase-1 (PFK-1). It is inhibited by ATP and citrate, and activated by AMP and fructose-2,6-bisphosphate.
During gluconeogenesis, which four enzymes bypass the three irreversible glycolytic steps?
Pyruvate carboxylase and PEP carboxykinase (bypass pyruvate kinase), fructose-1,6-bisphosphatase (bypass PFK-1), and glucose-6-phosphatase (bypass hexokinase/glucokinase).
Compare glycogenesis and glycogenolysis and their key enzymes.
Glycogenesis: glycogen synthesis via glycogen synthase (forms $\alpha(1\to4)$ bonds), using UDP-glucose. Glycogenolysis: glycogen breakdown via glycogen phosphorylase, releasing glucose-1-phosphate.
What is the primary product and purpose of the pentose phosphate pathway (PPP)?
It produces NADPH (for reductive biosynthesis and antioxidant defense) and ribose-5-phosphate (for nucleotide synthesis). Its rate-limiting enzyme is glucose-6-phosphate dehydrogenase.
Define saturated vs unsaturated fatty acids and their effect on melting point.
Saturated fatty acids have no $\ce{C=C}$ double bonds (straight chains, pack tightly, higher melting point). Unsaturated fatty acids have one or more $\ce{C=C}$ bonds (cis bonds cause kinks, lower melting point).
What is the general structure of a triglyceride (triacylglycerol)?
A glycerol backbone esterified to three fatty acid chains via ester bonds; it is the primary energy-storage lipid.
Describe the amphipathic structure of a phospholipid and its role in membranes.
A phospholipid has a polar (hydrophilic) phosphate-containing head and two nonpolar (hydrophobic) fatty acid tails. This amphipathicity drives formation of the lipid bilayer, with heads facing water and tails inward.
What is the characteristic core structure of all steroids, and name key examples.
A fused four-ring structure: three cyclohexane rings and one cyclopentane ring (the steroid/gonane nucleus). Examples: cholesterol, testosterone, estrogen, cortisol, aldosterone.
What is the metabolic precursor of all steroid hormones, and how is it derived?
Cholesterol. It is the precursor to the steroid hormones and is synthesized in the cytosol from acetyl-CoA (via the rate-limiting enzyme HMG-CoA reductase).
Summarize the steps and net ATP yield of one turn of beta-oxidation for a fatty acid.
Each cycle: oxidation, hydration, oxidation, thiolysis; it shortens the chain by two carbons and yields $1$ acetyl-CoA, $1$ FADH$_2$, and $1$ NADH per cycle.
Where does fatty acid synthesis occur, what is its rate-limiting enzyme, and what reductant does it use?
In the cytosol, using acetyl-CoA and NADPH. The rate-limiting enzyme is acetyl-CoA carboxylase, which converts acetyl-CoA to malonyl-CoA.
Name the three ketone bodies and the condition that promotes their formation.
Acetoacetate, beta-hydroxybutyrate, and acetone. They form during prolonged fasting/starvation or untreated diabetes, when excess acetyl-CoA from fat breakdown exceeds citric acid cycle capacity.
Compare the density and function of chylomicrons, VLDL, LDL, and HDL.
Chylomicrons: lowest density, carry dietary triglycerides from gut. VLDL: carry endogenous triglycerides from liver. LDL: cholesterol-rich, deliver cholesterol to tissues ('bad'). HDL: highest density (most protein), return cholesterol to liver ('good').
State the base-pairing rules in DNA and the number of hydrogen bonds in each pair.
Adenine pairs with thymine via $2$ hydrogen bonds; guanine pairs with cytosine via $3$ hydrogen bonds (Chargaff's rules: $[A]=[T]$ and $[G]=[C]$).
List the key structural differences between DNA and RNA.
DNA: deoxyribose sugar, thymine base, usually double-stranded. RNA: ribose sugar (2'-OH), uracil instead of thymine, usually single-stranded.
Distinguish purines from pyrimidines and list which bases belong to each.
Purines are double-ring bases: adenine and guanine. Pyrimidines are single-ring bases: cytosine, thymine, and uracil. (Mnemonic: 'PURe As Gold' for purines.)
Contrast the de novo and salvage pathways of nucleotide metabolism.
De novo synthesis builds nucleotides from scratch using amino acids, ribose-5-phosphate (PRPP), $\ce{CO2}$, and one-carbon units (energetically costly). The salvage pathway recycles free bases and nucleosides from degradation, saving energy.
What is the end product of purine catabolism in humans, and which disease results from its excess?
Uric acid is the final product of purine degradation. Its overaccumulation and crystallization in joints causes gout.
Name common cofactors/coenzymes and the vitamins they derive from: FAD, NAD+, coenzyme A, TPP.
FAD from riboflavin (B$_2$); NAD$^+$ from niacin (B$_3$); coenzyme A from pantothenic acid (B$_5$); thiamine pyrophosphate (TPP) from thiamine (B$_1$). Cofactors are inorganic (e.g., metal ions like $\ce{Zn^2+}$, $\ce{Mg^2+}$); coenzymes are organic.
What this deck covers
The Biochemistry deck follows the MCAT Biochemistry syllabus — 13 chapters and 48 topics — so questions land on material that is genuinely examinable rather than trivia around it. That works out to roughly 3.9 cards per chapter.
Answers are written to be recallable, not just readable — averaging about 171 characters, which is long enough to carry the reasoning and short enough to say out loud.
A deck like this earns its keep on the second and third pass. Read the syllabus first so you know the shape of the subject, then use the cards to find the specific facts that have not stuck.
Biochemistry flashcards FAQ
How many Biochemistry flashcards are in this MCAT deck?
51 cards. This page previews 24 of them, sampled evenly across the deck so you can judge the difficulty before installing anything.
Are these MCAT flashcards free?
Yes. The preview here is free to read with no signup, and the full 51-card deck is free inside the Examius app.
What do the Biochemistry cards cover?
They follow the MCAT Biochemistry syllabus — 13 chapters and 48 topics — so the questions track what is actually examinable.
How should I use these flashcards?
Read the syllabus first so you know the shape of the subject, then drill the deck. Examius schedules each card with spaced repetition, so cards you keep missing come back sooner and ones you know drift further apart.