F. Enzymes digestion and absorption Flashcards
Name the components of proteins
amino acid monomers form polypeptide chains which form proteins
Draw the structure of an amino acid
……………...R ……………….| H2N-------C-------COOH …………...….| …………..….H
How are dipeptides made
The condensation of two amino acids
Name the bond that forms between two amino acids
peptide
How many polypeptides does a functional protein contain
one or more
Name all 4 bonds present in a protein
peptide (between amino acids)
hydrogen (hold together proteins secondary and tertiary shape)
disulfide bridges (hold together proteins tertiary structure)
ionic bonds (hold together proteins tertiary structure)
Describe the primary structure of a protein
A polypeptide chain of amino acids joined by peptide bonds formed in a condensation reaction.
Why is a proteins primary structure important
- the primary structure that determines a proteins shape and therefore function
- single change in the polypeptide chain causes bonds formed in different places
- changing the proteins tertiary shape which may
- cause it to function less well or differently
- as a proteins shape is very specific to its function.
Describe the secondary structure of a protein
When amino acids are joined by peptide bonds they become polar. This allows hydrogen bonds to form (between the H d+ of -NH and O d- of C=O) between amino acids in the polypeptide chain causing it to form alpha helixes or beta plated sheets.
Describe the tertiary structure of a protein
Beta plated sheets and alpha helixes form a more specific shape which is known as the proteins tertiary structure. This is stabilized by disulfide bridges, ionic bonds and hydrogen bonds.
Describe the quaternary of a protein
complex molecules containing a number of polypeptide chains and even groups not associated with proteins such as the iron group in haemoglobin (prosthetic group). This is held together by hydrogen ionic bond + disulfide bridges
Describe a test for protein
Add biuret reagent to sample
Describe a positive and negative result for the protein test
Positive: solution turns purple
Negative: solution remains blue
Name two types of basic protein shapes and their functions
1) Fibrous proteins (eg. collagen)- structural functions
2) Globular proteins (eg. enzymes and haemoglobin)- carry out metabolic reactions
Definition: enzyme
globular proteins that act as a biological catalyst
Definition: catalyst
catalysts are substances that alter the rate of reaction without altering themselves by lowing the activation energy of the reaction
Describe the induced-fit model of enzyme action.
the induced fit model proposes the proximity of the substrate leads to a change in the enzyme that forms the functional active site so that it becomes complementary to the substrate and can bind
Name the earlier outdated enzyme action model
The lock and key model
Why was the lock and key model replaced with the induced fit model
The lock and key model suggests enzymes are rigid structures.
However, scientists have observed that other molecules could bind to enzymes at sites other than the active site,
which changed the enzymes activity.
This suggests the enzyme shape is being altered and that enzymes are a flexible structure (not as the lock and key suggests)
which caused the lock and key model to be replaced by the induced fit model
Describe and explain the effect of temperature on enzyme action
At first a rise in temperature increases rate of reaction,
as molecules have more kinetic energy.
This means more enzyme substrate complexes per unit time are formed,
as enzymes successfully collide more frequently with substrate molecules.
However, the rate begins to decrease,
as the temperature causes bonds (eg. hydrogen bonds) to break
resulting in the enzymes active site to change.
Eventually the enzyme denatures (permanently) and the reaction ceases.
Describe and explain the effect of pH on enzyme action
A change in pH (from the enzymes optimum pH) alters the charges on the amino acids
this breaks the bonds stabilizing the enzymes tertiary structure causing the active site to change shape.
This means less enzyme substrate complexes are formed per unit time resulting in a decreased rate of reaction.
Describe and explain the effect of enzyme concentration on the rate of reaction.
When there is excess substrate, an increase of enzyme concentration is proportionate to the rate of reaction.
This is because more substrate molecules are now being acted on at once.
However if there is limiting substrate increasing enzyme concentration wont effect the rate of reaction.
This is because there are enough active sites to accommodate all remaining substrate.
Describe and explain the effect of substrate concentration on the rate of reaction.
When enzyme concentration is fixed, an increase in substrate is proportionate to the rate of reaction.
This is because at low concentrations there are excess enzymes not acting on a substrate and an increase in substrate would mean more substrate is being acted on at once.
However at a certain point substrate concentration wont have an effect on reaction rate as there is a limited amount of enzyme and all the active sites are being occupied at one time.
Definition: competitive inhibitor
a molecule that binds to the active site of an enzyme
