Proteins, Enzymes, and Nucleic Acids

Monomer of a protein

Amino acid

Monomer of a nucleic acid

Nucleotide

Monomer of a carbohydrate

Monosaccharide

Monomer of a lipid

Fatty acid

Elements in carbohydrates and lipids

C, H, O

Elements in proteins

C, H, O, N (sometimes S)

Elements in nucleic acids

C, H, O, N, P

Major use of carbohydrates

Energy

Major use of lipids

Long-term energy storage and cell membranes

Major use of proteins

Body structures and enzymes

Major use of nucleic acids

Storing information and coding for proteins

5 parts of an amino acid

Central carbon, amino group, carboxyl group, hydrogen, R group (side chain)

Which part of an amino acid differs between the 20 types?

The R group

Do all amino acids contain sulfur?

No. Only some do (such as cysteine and methionine).

Nonpolar R group: water relationship and folding

Hydrophobic; folds inward

Polar R group: water relationship and folding

Hydrophilic; folds outward

Electrically charged R group behavior

Hydrophilic; forms ionic bonds with each other or folds outward and interacts with water

What determines protein shape?

The properties of the amino acids' R groups

How are amino acids joined into proteins?

Dehydration synthesis, which releases H2O

Peptide bond

Covalent bond between the carboxyl group of one amino acid and the amino group of the next

Dipeptide

Two amino acids joined by a peptide bond

Protein function: build structures (examples)

Elastin, collagen, keratin

Protein function: store food/energy (examples)

Ovalbumin, casein

Protein function: transport or move substances (examples)

Hemoglobin, cell membrane proteins

Protein function: coordinate body activities (example)

Insulin

Protein function: contract/move (examples)

Actin, myosin

Protein function: fight diseases (examples)

Antibodies: IgE, IgA, IgG

Protein function: control chemical reactions (examples)

Enzymes such as amylase and proteases

Enzyme

A protein that acts as a catalyst to speed up a reaction

Are enzymes used up in a reaction?

No. They are not consumed and can be reused.

Enzyme names usually end in…

-ase (sucrase, lipase, amylase)

Catalyst

Something that speeds up a reaction without being used up

Activation energy (Ea)

The energy needed to get a reaction started

How do enzymes speed up reactions?

By lowering the activation energy

Endothermic reaction

Absorbs energy

Exothermic reaction

Releases energy

Substrate

The reactant the enzyme binds to

Active site

The region of the enzyme where the substrate binds

Enzyme-substrate complex

The enzyme and substrate attached together

Induced fit

The active site slightly changes shape to wrap around the substrate

Why is an enzyme specific to one substrate?

Its active site shape matches only that substrate (or a few)

What determines an enzyme's shape?

The folding of the protein, based on the R groups of its amino acids

Enzyme cycle: 5 steps

1) Substrates enter active site 2) Held by weak interactions 3) Converted to products 4) Products released 5) Active site available again

Sucrase reaction

Sucrose + H2O becomes glucose + fructose

Lipase reaction

Triglyceride + H2O becomes 3 fatty acids + glycerol

Denature

To lose 3D shape so the enzyme can no longer bind its substrate

What denatures an enzyme?

High temperature or pH far above or below the optimum

Effect of low temperature on enzymes

Slows kinetic energy and the reaction rate but does not denature the enzyme

Why is there a limit to the effect of temperature?

Past the optimum, heat breaks the bonds that hold the enzyme's shape and it denatures

Optimal temperature for typical human enzymes

About 35-37 degrees C

Effect of increasing enzyme concentration (substrate in excess)

Reaction rate increases in a straight line (more active sites)

Effect of increasing substrate concentration

Rate rises, then levels off at the saturation point

Saturation point

The point where all enzyme active sites are occupied

Why does the rate level off as substrate increases?

All active sites are full, so extra substrate cannot speed up the reaction

What would level off a rate as enzyme concentration increases?

Substrate becoming limited

What does hypothermia do to enzymes?

Slows enzyme activity (cold slows molecules but does not denature)

Nucleic acid function

Store and transmit hereditary information (genes)

3 parts of a nucleotide

Phosphate group, 5-carbon (pentose) sugar, nitrogen base

Which part of a nucleotide varies?

The nitrogen base

Sugar in DNA

Deoxyribose

Sugar in RNA

Ribose

DNA stands for

Deoxyribonucleic acid

RNA stands for

Ribonucleic acid

DNA structure

Double helix (two strands); stores the genetic information

RNA structure

Single strand; transmits the genetic information

Bases in DNA

Adenine, thymine, guanine, cytosine

Bases in RNA

Adenine, uracil, guanine, cytosine

Purines

Double-ring bases: adenine (A) and guanine (G)

Pyrimidines

Single-ring bases: cytosine (C), thymine (T), uracil (U)

Memory trick for purines

Pure As Gold (A and G)

DNA base pairs

A pairs with T; G pairs with C

RNA base pairs

A pairs with U; G pairs with C

Hydrogen bonds in A-T pair

2

Hydrogen bonds in G-C pair

3

Base pairing memory tricks

Apples in Trees (A-T); Cars in Garage (C-G)

Chargaff's rule

Within a species, %A = %T and %G = %C

DNA backbone (outsides)

Sugar + phosphate

DNA rungs (middle)

Nitrogenous bases

What holds the two DNA strands together?

Hydrogen bonds (weak bonds between bases)

Why can DNA strands separate?

For DNA replication (hydrogen bonds are weak)

Complementary strand of A-A-T-G-C

T-T-A-C-G

What does "complementary" mean for DNA?

Bases on opposite strands match by the pairing rule

Reactants

The chemicals you start with before a reaction

Products

The new chemicals made at the end of a reaction

Hydrophobic

Water-avoiding (nonpolar)

Hydrophilic

Water-attracting (polar or charged)

Which element is in nucleic acids but not proteins?

Phosphorus (P)

Which element is in only some proteins?

Sulfur (S)

Which bases pair: a purine with a…

Pyrimidine (a double ring with a single ring)

Where are the bases in a DNA molecule?

In the middle, as the rungs of the ladder

Gene

A section of DNA that carries hereditary information

Enzyme graph: why does activity drop after the optimum temperature?

Denaturation; the enzyme loses its shape

Do enzymes change the energy of the reactants and products?

No. They only lower the activation energy.

What does the active site of an enzyme do?

Binds the substrate so it can be converted to products

Claim-Evidence-Reasoning for a graph question

Claim = what happens; Evidence = value from the graph; Reasoning = how enzyme shape explains it