BioChemistry Preliminary Exam

Chemical equation

Representation of a reaction showing the reactants and products.

Irreversible reactions

Represented by a single arrow.

Reversible reactions

Represented by a bidirectional arrow.

Arrow points to right

Forward reaction.

Arrow points to left

Reverse reaction.

Reactions -> Products

Format for irreversible reactions.

Reactants ⇌ Products

Format for reversible reactions.

Heat

Transfer of thermal energy.

Exothermic Processes

Release of heat to the surroundings.

Endothermic Processes

Absorption of heat.

Thermodynamics

Study of heat conversion to and from other forms of energy.

1st Law of Thermodynamics

Energy cannot be created or destroyed, only converted.

2nd Law of Thermodynamics

Entropy always increases.

Entropy

Measure of randomness or disorder of substances.

Oxidation

Loss of electrons or hydrogen; gain of oxygen; releases energy.

Reduction

Gain of electrons or hydrogen; loss of oxygen; stores energy.

Water

Predominant component of living organisms; has tetrahedral geometry.

Hydrogen attached to S, O, or N

Forms hydrogen bonds; becomes polar and hydrophilic.

Polar

Uneven distribution of electrical charges.

Non-polar

Even distribution of electrical charges.

Molecules without hydrogen

Hydrophobic and non-polar.

Hydrophilic

Water-loving; dissolves easily; generally charged or polar.

Hydrophobic

Water-fearing; dissolves better in chloroform or benzene.

High Dielectric Constant

Increases force of attraction between charged/polar molecules.

Amphoteric

Acts as both an acid and a base.

H+

Makes water more acidic.

OH-

Makes water more basic (alkaline).

Acids and bases

Measured using negative log of hydrogen ion concentration.

pH

Potential of Hydrogen; measures acidity or alkalinity.

Acid

0-6.9 on pH scale; high H+; proton donor.

Base

7.1-14 on pH scale; low H+; proton acceptor.

Neutral

7 on pH scale; equal H+ and OH-; pure water.

Buffers

Resist changes in pH by neutralizing H+ or OH-; e.g., bicarbonate, phosphate, proteins.

Carbohydrates

Most abundant biological molecule; general formula Cn(H2O)n.

Major energy source

Glucose (monosaccharide).

Cellular respiration

Pathway for glucose breakdown: glycolysis, Krebs cycle, ETC.

Storage form of energy

Glycogen (polysaccharide).

Glycogen storage location

Liver and muscles.

Glycoprotein

Component of membranes used in cell signaling and recognition.

Primary roles of carbohydrates

Energy source; structural roles; fuel for brain and RBCs; signaling.

Monosaccharides

Simple sugar units.

Disaccharides

Two monosaccharide units.

Oligosaccharides

3 to 10 sugar units.

Polysaccharides

More than 10 sugar units; long sugar chains.

Triose

3-carbon sugar.

Tetrose

4-carbon sugar.

Pentose

5-carbon sugar.

Hexose

6-carbon sugar.

Heptose

7-carbon sugar.

Nonose

9-carbon sugar.

Glucose

Main fuel for brain and body; universal fetal fuel.

Fructose

Fruit sugar; builds up in fructose intolerance.

Galactose

From lactose; made in mammary glands; used in glycolipids and glycoproteins.

Mannose

Used in glycoproteins.

Ribose

Found in nucleic acids and coenzymes.

Deoxyribose

Ribose lacking hydroxyl at carbon 2.

Xylulose

Excreted in urine in pentosuria.

Disaccharide examples

Sucrose, Maltose, Lactose.

Polysaccharide examples

Glycogen, Starch, Cellulose.

Hexoses

Glucose, Fructose, Galactose, Mannose.

Pentoses

Ribose, Xylulose.

Important sugar types

Trioses, pentoses, hexoses.

Aldoses

Contain aldehyde group; at the end of the carbon chain.

Ketoses

Contain keto group; within the carbon chain.

Isomers

Same formula, different structure; e.g., fructose, galactose, mannose, glucose.

Epimers

Differ at one carbon; e.g., glucose-galactose (C-4), glucose-mannose (C-2).

Anomers

Alpha or beta ring forms of monosaccharides; formed by rotation at carbonyl carbon.

Mutarotation

Conversion between alpha and beta anomers in solution.

Pyranose

6-membered ring sugar.

Furanose

5-membered ring sugar.

Enantiomers

Mirror image sugars (D and L forms).

D-sugar

Dextrorotatory form.

L-sugar

Levorotatory form.

Sucrose

Glucose and fructose.

Lactose

Galactose and glucose.

Maltose

Glucose and glucose.

Cellulose

Main component of plant cell walls.

Chitin

Found in insect exoskeletons and fungal cell walls.

Glycogen

Animal/human energy storage; composed of glucose.

Starch

Plant energy storage; made of amylose and amylopectin.

Glycosidic bonds

Links sugar units.

Glycosyltransferases

Form glycosidic bonds using nucleotide sugars.

Amylase

Breaks down glycosidic bonds.

Sites of carbohydrate digestion

Mouth and intestinal lumen.

Digestive enzymes

Glycoside hydrolases; hydrolyze glycosidic bonds.

Pancreatic α-amylase

Continues starch digestion in small intestine after pH neutralization.

Intestinal disaccharidases

Break down disaccharides in the duodenum and jejunum.

Final site of digestion

Mucosal lining of duodenum and upper jejunum.

Primary site of absorption

Upper jejunum.

Galactose and glucose absorption

Secondary active transport with sodium ions via SGLT-1.

Glucose transporters

Help glucose enter cells.

GLUT1

RBCs, brain, cornea, placenta; no insulin required.

GLUT2

Liver, kidney, GI tract, pancreas β-cells; no insulin required.

GLUT3

Brain, placenta; no insulin required.

GLUT4

Skeletal and heart muscle, adipose tissue; insulin required.

GLUT5

Small intestine, sperm cells; absorbs fructose; no insulin required.

SGLT1

Intestinal mucosa, renal tubules; sodium-dependent glucose/galactose uptake.

SGLT2

Renal tubules; glucose reabsorption; no insulin required.

Type 1 Diabetes Mellitus

Glucose can’t enter muscle/fat; remains in blood (hyperglycemia).

Lactose intolerance

Lack of lactase enzyme; common in adults worldwide.