Biochemistry: Unit Review

Rough ER (made on ribosomes, enters the ER) → transport vesicle → Golgi apparatus (modified, sorted) → secretory vesicle → fused with the cell membrane (exocytosis).

Lysosomal enzymes work best at acidic pH. If they leak into the neutral cytosol, they work poorly, so they do little damage.

Mitochondria and chloroplasts.

Many of them together hold the two DNA strands together and help hold protein shapes, yet each one can be broken easily, so DNA can unzip and proteins can change shape when needed.

Carboxyl; amino; hydroxyl.

Water is polar: its partial negative O and partial positive H atoms are attracted to ions and polar groups, surrounding them (hydration) so they dissolve.

The carboxyl group: it can release H⁺, becoming –COO⁻.

Condensation (dehydration synthesis).

The substance that is oxidized ("OIL RIG": oxidation is loss).

Reduced: it gained electrons (carried with hydrogen).

Water and a salt.

A glycosidic bond (glycosidic linkage).

Starch has α glycosidic bonds that our enzymes (amylase) can hydrolyze. Cellulose has β linkages, and humans have no enzyme that breaks them.

Glucose and fructose.

Their cis double bonds put kinks in the fatty-acid tails, so the molecules can't pack tightly; weaker attractions mean a lower melting point.

A hydrophilic phosphate head and two hydrophobic fatty-acid tails. In water, they form a bilayer with heads facing the water and tails hidden inside.

Cholesterol: part of animal cell membranes, helps keep fluidity steady, and is used to make steroid hormones. (Or testosterone/estrogen: hormones.)

Hydrogen bonds between the backbone C=O and N–H groups (forming α-helices and β-pleated sheets).

Primary: the amino acid sequence. Secondary: helices and sheets from backbone H-bonds. Tertiary: the overall 3-D fold from R-group interactions. Quaternary: several polypeptides joined.

Heat denatures it: it breaks the weak bonds that hold the 3-D shape, so the active site changes shape and the substrate no longer fits.

A phosphate group, a five-carbon sugar (deoxyribose or ribose) and a nitrogenous base.

A = T = 30%, so A + T = 60%. G + C = 40%, so G = 20%.

Any two: DNA has deoxyribose, RNA has ribose; DNA has thymine, RNA has uracil; DNA is usually double-stranded, RNA usually single-stranded.

Hydrolysis of its terminal phosphate (ATP → ADP + Pᵢ) releases energy that the cell couples to work such as active transport and building molecules.

Iodine (Lugol's) solution turns blue-black.

A reducing sugar (such as glucose, fructose, maltose or lactose) is present.

A negative control shows what a result looks like with no biochemical present, so you can tell a true colour change from the reagent's own colour.

Biuret reagent turns violet/purple.

They lower the activation energy by binding the substrate in the active site and stabilizing the transition state. They do not change the overall free-energy change (ΔG).

The active site is not a rigid lock: when the substrate binds, the enzyme changes shape slightly to fit it more tightly, straining bonds and helping the reaction.

A cofactor is any non-protein helper an enzyme needs; a coenzyme is an organic cofactor, often made from a vitamin (e.g. NAD⁺). Inorganic cofactors include metal ions such as Zn²⁺ or Mg²⁺.

A competitive inhibitor competes for the active site, so more substrate outcompetes it. A non-competitive inhibitor binds elsewhere and changes the enzyme's shape, so more substrate can't restore activity.

The end product of a pathway inhibits an early enzyme (often allosterically), so the cell stops making more product when it has enough.

A molecule that binds an allosteric site (not the active site) and stabilizes the active shape of the enzyme, increasing its activity.

Independent: temperature. Dependent: rate of oxygen production.

Any two: enzyme concentration, substrate concentration, pH, volume, time measured, source of enzyme.

To reduce the effect of random error and check that results are reliable (repeatable).

Phospholipids and many proteins move sideways within the layer; the membrane is not rigid.

It acts as a fluidity buffer: it limits movement at warm temperatures and prevents tight packing at cold temperatures.

Small, nonpolar molecules such as O₂ and CO₂.

Water moves into the cell by osmosis (more water outside, relatively), so the cell swells and may burst (lysis).

It uses channel or carrier proteins to move particles that can't cross the bilayer easily (ions, glucose). It is still passive: down the gradient, no ATP.

0.1 mol/L is hypotonic to the potato cells, so water enters. 0.5 mol/L is hypertonic, so water leaves.

3 Na⁺ out and 2 K⁺ in, using one ATP.

Using the energy of an ion gradient (made by a pump) to move another substance against its gradient, such as the Na⁺-glucose symporter.

Phagocytosis, a type of endocytosis.

It cuts κ-casein, a milk protein, so the other caseins clump into curds, which are separated from the whey.

So they can be reused, separated easily from the product, and often stabilized, lowering cost.

They work at lower temperatures, so less energy is used to heat water (and less harsh chemicals are needed).

It blocks the ATP-binding site of the overactive BCR-ABL kinase, stopping the signal that tells cells to divide.

It is a radioactive glucose look-alike; many active cancer cells take up more glucose, so they collect more FDG.

Any two: evidence of effectiveness, benefits, risks, cost and access, ethics, environmental impact.