1.4 Proteins

Define amino acids

Monomers from which protein is made of

What determines the functions of proteins, and makes them different from each other?

Their 3D shape

Draw the general structure of an amino acid

How many different amino acids are there?

20

What is the only thing the 20 amino acids differ on?

R-group/ side group

What does a condensation reaction between amino acids form?

Peptide bond

Describe how dipeptides are formed

Joining of two amino acids by a condensation reaction

Describe how polypeptides are formed

Condensation of MANY amino acids

Draw the formation of a dipeptide

What are the four levels of structure in a protein?

Primary, secondary, tertiary, quaternary

Define the primary structure of a protein

Order/sequence of the amino acids in a polypeptide chain held by peptide bonds

What happens after the primary structure of protein made?

It is transported to golgi body by RER where it gets processed into secondary structure (alpha helix or beta pleated sheet)

Define the secondary structure of a protein

The sequence of amino acids causes parts of a protein molecule to bend into alpha helix shapes or fold into beta pleated sheets. Hydrogen bonds hold the secondary structure

Where do the hydrogen bonds form in the secondary structure of a protein?

Between different amino acids and between O-H. O in the c double bond of the carboxyl group and H in amine group

Define the tertiary structure of a protein

The further folding of the secondary structure which forms a unique 3D shape that is held in place by ionic, hydrogen and disulfied bonds

Where do the ionic and disulfide bonds of the tertiary structure of a protein form?

Between the R-groups of different amino acids

Why do disulfide bonds only form sometimes?

Must be a sulfur in the R groups for the bond to occur S—S

Define the quaternary structure of a protein

Protein made up from more than one polypeptide chain

Give an example of a protein made of 4 polypeptide chains

Haemoglobin

Explain the importance of the primary structure

If one amino acid in sequence is different, then it will cause the ionic/hydrogen/disulfide bonds to form in different locations, resulting in a different 3D shape

What impact will having on amino acid in sequence different in enzymes

Different shape of active site so non-functioning

What impact will having on amino acid in sequence different in carrier proteins

Different shaped binding site so molecules no longer complementary and cannot be transported across membranes

Describe the test for proteins

Add biuret reagent. Positive test observation is solution turning from blue to purple

Define enzymes

Tertiary structure proteins which catalyze reactions by lowering the activation energy

Describe role and structure of active site

Specific and unique in shape due to the specific bonding and folding in tertiary structure of the protein. Due to specific active site, enzymes attach only to substrates complementary in shape

Name two models which explain enzyme action

Lock and key model, Induced fit model

Explain the lock and key model

Model that suggests enzyme is like a lock, substrate is like key that fits into it due to complementary shape. Enzymes active site is a FIXED shape and due to random collisions the substrate can collide & attach to enzyme, forming an enzyme-substrate complex. Charged groups in active site distort the substrate lowering activation energy, products released

Explain the induced fit model

Model suggests enzyme is like a glove and substrate is hand. Empty glove is not exactly complementary in shape to hand, when hand enters it enable glove to mold around hand and become completely complementary. Enzyme active site is induced/slightly changes shape to mold around substrate. Enzyme-substrate occurs due to enzyme molding around substrate putting strain on bonds, lowering the activation energy. Products removed and enzyme active site returns to og shape

State the factors that affect enzymes

Temperature, pH, substrate concentration, enzyme concentration, inhibitors

Explain how temperature affects enzymes

If temperature too low, not enough kinetic energy for successful collisions between the enzyme and substrate. If the temperature is too high, enzymes denature, active site changes shape because tertiary structure bonds break, and enzyme -substrate complexes cannot form

Explain how pH affects enzymes

Too high or too low pH will interfere with the charges in the amino acids in active site. This can break the bonds holding the tertiary structure in place and therefore the active site changes shape. The enzyme denatures and fewer enzyme-substrate complexes form. Different enzymes have different optimal pH

What does it mean when you have too high a pH?

too many OH- ions

What does it mean when you have too low pH?

Have too many H+ ions

Explain how substrate and enzyme concentration affects enzymes

If there is insufficient substrate, the reaction will be slower as there will be fewer collisions between enzyme and substrate. If there are insufficient enzymes, then the enzymes active sites will become saturated with substrate and unable to work any faster than Vmax

Explain how enzyme inhibitors affect enzymes

Competitive inhibitors- similar in shape to substrate and can bind to active site, preventing substrate from binding and reaction occurring. Add more substrates to flood inhibitor and knock them out of active site. Non competitive inhibitor- bind to enzyme in allosteric site, causing active site to change shape/change in tertiary structure, substrate no longer complementary in shape so can longer bind to active site regardless substrate conc