MCAT Biochemistry

Macromolecules

Are polymers made from monomers - enzymes that make polymers are polymerases via reactions called polymerization.

Proteins

made up of amino acids(20 kinds)

• Have an N-C-C backbone, amine group, carboxylic group, and variable group

• Bond together by a peptide bond(formed by dehydration synthesis - loss of H2O)

Protein Structures(4)

• Primary = amino acids joined

• Secondary = alpha-helix or beta-sheets

• Tertiary: formation of a polypeptide and side chain interactions - inner core becomes hydrophobic and outer becomes hydrophilic

  • Non-covalent interactions: non-polar/non-polar, polar neutral/polar neutral, acid/base(charged)

  • Covalent: disulphide bridges(harder to break)

• Quaternary structure: side chain interactions between different polypeptides - subunits come to form larger units

Carbohydrates

Made from monosaccharides to disaccharides to polysaccharides

Monosaccharide

CnH2On - 3 common are glucose, fructose, galactose - ribose and deoxyribose

Disaccharide

2 monosaccharides - 3 common = maltose, sucrose, lactose - C12H22O11 formula

Polysaccharides

Made of many monosaccharides - 3 common are glycogen, starch, and cellulose - function as an energy source

Lipids

The fats - made of a hydrocarbon structure(many C and H)

Unsaturated

Have space for more H to bind - liquid at room temp

saturated fatty acids

No more space for H to bind - are solid at room temperature

Triglyceride

3 fatty acids combined

Phospholipids

2 lipid structures and one phosphate - form the lipid bilayer due to having polar and non-polar sides

Terpenes

built from isoprene structures and need at least 2 of them - terpenes form waxes and lipid rings like vitamin A

Cholesterol and steroid hormones

3 six-carbon rings and 1 five-carbon ring)

Thermodynamics

the study of the relations between heat, work, temperature, and energy

ΔG

• When G<0 = negative G, spontaneous - gives E

• When G>0 = positive, non-spontaneous - needs E

When G = 0, equilibrium

Reaction Coupling

Using ATP as a source of energy - a very favourable reaction is used to drive an unfavourable one

• ATP = ADP + Pi → very exergonic

  • Exergonic = giving off E

  • Endergonic = using up E

Chemical Kinetics

The study of reaction rates - all reaction rates proceed through a transition state which tends to be unstable

Activation Energy

Is the required E to produce the TS

• if Ea is High = slow rate

• if Ea is low = faster rate

Reaction Coordinate Graph

shows the energy vs reaction coordinates over time - the smaller the Ea, the better

• We can make the Ea smaller using catalysts - speeding the reaction up by stabilizing TS and reducing Ea

Enzymes

a physiological catalyst - works to speed up a reaction by increasing the rate of reaction, not used up in a reaction, a must be specific

Enzyme Structure

an enzyme has an allosteric site and an active site - the active site is where the substrate binds(where the reaction occurs) and the allosteric site is another place for enzyme regulation)inhibition or activation)

• Two models - active site and induced fit; active is lock and key while the induced fit is when the enzyme needs to change shape to fit a substrate

• Can perform both positive and negative feedback

Enzyme Function and regulation

• Function: to speed up a reaction

• Regulation: by many inhibitions ways, allosteric site, feedback inhibitionV vs. [S] Graph

V vs. [S] Graph

the reaction rate in Velocity vs the substrate concentration [S] → vmax is when the enzyme is saturated and depends on enzyme [C], and the [S] becomes constant - Vmax/2 is when the linear part of the graph is equal to [S]. Km is the substrate [S] required to reach ½ Vmax

Competitive Inhibition

Compete for enzyme binding - same Vmax but the effect on Km is more since you need more substrate - a longer time to reach the same Km - binds at the active site

Non-competitive Inhibition

it affects the Vmax since we need more enzymes to deal with the substrate, but Km is unchanged since the active site is the same but prevents the activity of the enzyme- binds to the allosteric site

Un-competitive Inhibition

it affects both the Vmax and Km since it binds to the allosteric site after the substrate is bound, which affects both enzyme performance and the amount of product being produced - binds to an allosteric site

Mixed-Type Inhibition

binds at the allosteric site either when the enzyme is bound to the substrate or empty the active site. Vmax will become lowered, but Km can vary whether enzyme bound or empty Active site

• when bound to the substrate, Km decreases(like un-comp)

• When an empty active site, Km increases(like comp

Lineweaver Burk Plots