3.1.4 Proteins for A-Level Biology (AQA)

What type of biological monomer joins together to form proteins?

Amino acids

Proteins are polymers formed from chains of amino acids linked together.

How well did you know this?

Not at all

Perfectly

What functional group is represented by NH₂ in the general structure of an amino acid?

Amine group

This basic group contains nitrogen and can accept a hydrogen ion.

How well did you know this?

Not at all

Perfectly

What functional group is represented by COOH in an amino acid?

Carboxyl group

This acidic group can donate a hydrogen ion in solution.

How well did you know this?

Not at all

Perfectly

Fill in the blank:

The part of an amino acid that differs between different amino acids is the ______ group.

R group

The R group (side chain) determines the chemical properties of the amino acid.

How well did you know this?

Not at all

Perfectly

What type of bond forms when two amino acids join together?

Peptide bond

This bond forms during a condensation reaction between the amine group of one amino acid and the carboxyl group of another.

How well did you know this?

Not at all

Perfectly

Fill in the blank:

A ______ reaction occurs when two amino acids join to form a peptide bond.

Condensation

A molecule of water is released when the bond forms.

How well did you know this?

Not at all

Perfectly

What molecule is formed when two amino acids join together?

Dipeptide

A dipeptide contains two amino acids linked by one peptide bond.

How well did you know this?

Not at all

Perfectly

What name is given to a long chain of many amino acids joined together?

Polypeptide

Polypeptides may fold to form functional proteins.

How well did you know this?

Not at all

Perfectly

A functional protein may consist of one or more what type of chain?

Polypeptides

Some proteins contain multiple polypeptide subunits.

How well did you know this?

Not at all

Perfectly

What level of protein structure refers to the sequence of amino acids in a polypeptide chain?

Primary structure

The order of amino acids is determined by the DNA sequence.

How well did you know this?

Not at all

Perfectly

What level of protein structure forms when a polypeptide chain coils into an α-helix or folds into a β-pleated sheet?

Secondary structure

Stabilised mainly by hydrogen bonds between peptide bonds in the backbone.

How well did you know this?

Not at all

Perfectly

What level of protein structure describes the overall three-dimensional folding of a polypeptide?

Tertiary structure

Stabilised by hydrogen bonds, ionic bonds and disulfide bridges between R groups.

How well did you know this?

Not at all

Perfectly

What level of protein structure occurs when multiple polypeptide chains combine to form a functional protein?

Quaternary structure

Examples include haemoglobin, which contains multiple polypeptide subunits.

How well did you know this?

Not at all

Perfectly

Which type of bond forms between sulfur atoms in some amino acid side chains?

Disulfide bridge

These strong covalent bonds help stabilise the tertiary structure of proteins.

How well did you know this?

Not at all

Perfectly

Which type of bond forms between oppositely charged side chains in proteins?

Ionic bonds

These interactions contribute to stabilising tertiary structure.

How well did you know this?

Not at all

Perfectly

Which relatively weak bonds help stabilise both secondary and tertiary protein structures?

Study These Flashcards

Hydrogen bonds

Many hydrogen bonds together help maintain protein shape.

Why is protein structure important for protein function?

Study These Flashcards

They have a specific shape.

The precise 3D structure determines how the protein interacts with other molecules.

What chemical test is used to detect proteins in a sample?

Study These Flashcards

Biuret test

The test detects peptide bonds present in proteins.

Fill in the blank:

A positive Biuret test changes the solution from blue to ______.

Study These Flashcards

Purple

The colour change indicates the presence of peptide bonds in proteins.

True or False:

All proteins consist of only one polypeptide chain.

Study These Flashcards

False

Many proteins contain multiple polypeptide chains forming quaternary structure.

What type of biological molecule acts as a catalyst in living organisms?

Study These Flashcards

Enzymes

Enzymes are proteins that speed up biochemical reactions without being used up.

What effect does an enzyme have on the activation energy of a reaction?

Study These Flashcards

Lowers activation energy

By lowering activation energy, enzymes increase the rate of reactions.

What model describes how enzyme active sites change shape to fit a substrate during binding?

Study These Flashcards

Induced-fit model

The active site becomes more complementary to the substrate as binding occurs.

What region of an enzyme binds to the substrate during a reaction?

Study These Flashcards

Active site

The active site has a specific tertiary structure that allows substrate binding.

# Fill in the blank: When a **substrate** binds to an **enzyme**, an _\_\_\_\_\_\_ complex is formed.

Enzyme-substrate complex ## Footnote This temporary complex allows the reaction to occur more easily.

Why are enzymes considered highly **specific**?

They have an active site with a complementary shape which is coded for by the specific sequence of amino acids. ## Footnote The shape of the active site only fits particular substrates.

# True or False: Each **enzyme** usually catalyses only **one specific reaction**.

True ## Footnote Enzyme specificity arises from the precise structure of the active site.

What happens to the **rate** of an **enzyme-controlled reaction** when enzyme concentration increases (if substrate is abundant)?

Increases ## Footnote More enzyme molecules mean more available active sites.

How does increasing **substrate concentration** affect the **rate** of an enzyme-controlled reaction?

Increases, then plateaus. ## Footnote The rate rises until all enzyme active sites become occupied.

What type of **inhibitor** competes with the **substrate** for the active site of an enzyme?

Competitive inhibitor ## Footnote These inhibitors have a similar shape to the substrate.

What type of **inhibitor** binds to an enzyme at a site other than the **active site**?

Non-competitive inhibitor ## Footnote This binding alters the enzyme's shape and reduces its activity.

How does a **competitive inhibitor** affect **enzyme activity**?

Competes with the substrate. ## Footnote It reduces reaction rate by blocking substrate binding to the active site.

How does a **non-competitive inhibitor** affect **enzyme activity**?

Alters the shape of the active site. ## Footnote This prevents the substrate from binding effectively.

Why does **temperature** affect **enzyme-controlled reactions**?

It changes kinetic energy and enzyme structure. ## Footnote High temperatures can denature enzymes by breaking bonds that maintain their tertiary structure.

What happens to an **enzyme** when it becomes **denatured**?

Active site changes shape. ## Footnote The substrate can no longer bind, so the enzyme stops functioning.

Why does **pH** affect **enzyme activity**?

It alters bonds that maintain enzyme structure. ## Footnote Changes in pH can disrupt bonds that maintain the enzyme’s tertiary structure.

What formula can be used to calculate **pH** from **hydrogen ion concentration**?

pH = −log10[H⁺] ## Footnote This logarithmic relationship shows that small changes in pH represent large changes in H⁺ concentration.

What practical **investigation** is commonly used to study **enzymes** in AQA Biology?

Enzyme rate investigation ## Footnote Students measure how changing a variable affects the rate of an enzyme-controlled reaction.

What **mathematical method** can be used to determine the **initial rate** of an enzyme reaction from a graph?

Tangent method ## Footnote A tangent drawn at the start of the curve allows calculation of the initial rate.

3.1.4 Proteins Flashcards

Relate amino acid structure and levels of protein organisation to biological function and enzyme activity. (39 cards)