Proteins

Question 1

What are amino acids?

Answer 1

Subunits (monomers) of proteins

There are approximately 20 different amino acids found in proteins.

Question 2

What is the basic structure of all amino acids?

Answer 2

Amine group, Carboxyl group, Variable group

The ‘R’ groups of amino acids can have diverse properties.

Question 3

What type of properties does the R group of aspartic acid give?

Answer 3

Acidic properties

The structure includes a carboxyl group (COOH).

Question 4

What type of properties does the R group of lysine give?

Answer 4

Alkaline properties

The structure includes a long carbon chain and an amine group.

Question 5

What is a polypeptide chain?

Answer 5

A chain formed when amino acids are linked together via peptide bonds

Peptide bonds are formed between the amine and carboxylic acid groups of adjacent amino acids.

Question 6

What is a peptide bond?

Answer 6

A bond formed between the amine and carboxylic acid groups of adjacent amino acids

This bond is formed during condensation polymerization.

Question 7

What is formed when amino acids undergo condensation polymerization?

Answer 7

Dipeptide and water

The amine group loses a hydrogen atom, and the carboxylic acid group loses a hydroxyl group.

Question 8

What is the relationship between nucleic acids and proteins?

Answer 8

Amino acids as monomers of polypeptide chains

This relationship leads to the hierarchical levels of structure that give rise to functional proteins.

Question 9

What are the functions of proteins in organisms?

Answer 9

Diverse group of molecules, including enzymes as catalysts

Proteins collectively make an organism’s proteome.

Question 10

What organelles are involved in the export of proteins from a cell?

Answer 10

Rough endoplasmic reticulum, Golgi apparatus, associated vesicles

These organelles are part of the protein secretory pathway.

Question 11

Explain how proteins are synthesised.

Answer 11

Involves linking amino acids via peptide bonds

This process includes transcription and translation of genetic information.

Question 12

Draw and describe the four hierarchical levels of protein structure.

Answer 12

Primary, Secondary, Tertiary, Quaternary

Each level represents a different aspect of protein folding and function.

Question 13

What does protein denaturation refer to?

Answer 13

Loss of a protein’s three-dimensional structure

It usually results in a loss of function and is often irreversible.

Question 14

What are the agents that cause protein denaturation?

Answer 14

• Strong acids and alkalis
• Heavy metals
• Heat and radiation
• Detergents and solvents

An everyday example of protein denaturation is cooking eggs.

Question 15

What is the functional role of proteins in an organism?

Answer 15

• Structural
• Cellular signalling
• Motility
• Defence
• Transport
• Enzymes
• Cell-surface receptors

Each category has specific examples, such as collagen for structural and insulin for cellular signalling.

Question 16

What is the proteome?

Answer 16

The complete set of proteins produced by a single cell or organism

The study of interrelationships between proteins is called proteomics.

Question 17

What determines the final conformation of a protein?

Answer 17

The interactions of the ‘R’ groups of each amino acid

These interactions are crucial for the protein’s function.

Question 18

What are the four levels of protein structure?

Answer 18

• Primary structure (1°)
• Secondary structure (2°)
• Tertiary structure (3°)
• Quaternary structure (4°)

Each level describes different aspects of protein organization.

Question 19

Define primary structure in proteins.

Answer 19

The sequence of amino acids in a polypeptide chain

This sequence is critical for determining the protein’s final shape.

Question 20

What is the secondary structure of proteins?

Answer 20

The shape of the polypeptide chain (alpha-helix or beta-pleated sheet)

This structure is stabilized by hydrogen bonds.

Question 21

What does tertiary structure refer to in proteins?

Answer 21

The overall three-dimensional conformation of the polypeptide caused by folding

This structure is crucial for the protein’s function.

Question 22

What is meant by quaternary structure in proteins?

Answer 22

The association of multiple subunits of polypeptide chains

This structure is important for the function of multi-subunit proteins.

Question 23

What are the characteristics of fibrous proteins?

Answer 23

• Composed of long and narrow strands
• Have a structural role
• Water insoluble
• Very tough physically

They may be supple or stretchy and are organized in parallel chains.

Question 24

What are the properties of globular proteins?

Answer 24

• Compact and rounded shape
• Functional roles
• Easily soluble in water
• Tertiary structure is critical to function

Polypeptide chains are folded into a spherical shape.

Question 25

What is the first step in the **protein secretory pathway**?

Answer 25

Polypeptide produced on ribosome ## Footnote This marks the initiation of protein synthesis.

Question 26

After the polypeptide is produced, where does it enter next?

Answer 26

ER tubule ## Footnote The endoplasmic reticulum (ER) is crucial for further processing.

Question 27

What happens to the polypeptide in the **ER tubule environment**?

Answer 27

Polypeptide modified ## Footnote Modifications are essential for proper protein function.

Question 28

What encloses the polypeptide for transport?

Answer 28

Transport vesicle ## Footnote Vesicles are membrane-bound structures that facilitate transport.

Question 29

Where does further modification of the polypeptide occur?

Answer 29

Golgi apparatus ## Footnote The Golgi apparatus is key for final processing before export.

Question 30

What is the final step before a protein is ready for export?

Answer 30

Protein placed in transport vesicle ## Footnote This step prepares the protein for secretion.

Question 31

What happens to the protein transport vesicle at the plasma membrane?

Answer 31

Fuses with the plasma membrane ## Footnote This fusion is crucial for the release of the protein.

Question 32

What is **exocytosis**?

Answer 32

Process by which large substances exit the cell via a vesicle ## Footnote Exocytosis is vital for secreting proteins and other materials.

Question 33

What are **ribosomes** made up of?

Answer 33

* Protein * Ribosomal RNA (rRNA) ## Footnote Ribosomes can be free in the cytosol or attached to the ER.

Question 34

What is the role of the **endoplasmic reticulum**?

Answer 34

* Production * Processing * Modification * Transport * Storage ## Footnote The ER links with the cell membrane and other organelles.

Question 35

What type of proteins do **free ribosomes** produce?

Answer 35

Proteins for local use in the cell ## Footnote These proteins are not exported but used within the cell.

Question 36

What type of proteins do ribosomes on the **rough endoplasmic reticulum** produce?

Answer 36

Proteins transported to other parts of the cell or away from the cell ## Footnote These proteins are typically destined for export.

Question 37

What is the **Golgi apparatus** responsible for?

Answer 37

Final synthesis, modification, and packaging of proteins ## Footnote It prepares proteins for secretion in membrane-bound vesicles.

Question 38

Explain the relationship between DNA, RNA, Amino acids and proteins ?

Answer 38

Dna contains the instuctions (genes) for making proteins. A gene's base sequence is transcribed into mRNA. The mRNA is translated at the ribosome into a sequence of amino acids. Each group of three bases on mRNA encodes a specific amino acid. Amino acids are joined in the order specified by the mRNA to form a polypeptide chain. The polypeptide folds to form a functional protein.

Question 39

Identify the bonds that form between adjacent amino acids during protein synthesis, where does this occour?

Answer 39

Adjacent amino acids are joined by peptide bonds, these bonds form during translation at the ribosome.

Question 40

Explain why proteins are not ALL the same ?

Answer 40

- They differ in amino acid sequence - The variable R-group gives each amino acid different properties - Different sequences cause proteins to fold into different three-dimensional shapes - Protein shape determines functions - They all perform different functions

Question 41

What does it mean if an enzyme denatures?

Answer 41

- Denaturation is the loss of the enzymes normal three dimentional shape, - Hydrogen bonds, ionic bonds and hydrophobic interactions are broken. -Disulfide bonds may be disrupted under extreame conditions. -The primary Structure (peptide bonds between amino acids is not broken - as a result the active side changes shape

Question 42

2 conditions under which denaturation occours?

Answer 42

- Higher temperatures - Extreme pH ( very acidic or very alkaline)

Question 43

What is the function of ribosomes that are found free in the cytosol?

Answer 43

Free ribosomes produce proteins that are used locally within the cell

Question 44

What is the function of ribosomes that are attached to the endoplasmic reticulum ?

Answer 44

Ribosomes attached to ER produce proteins that need to be transported to distant parts of the cell, or exported out of the cell.

Question 45

What is the difference between a regulatory gene and a structural gene?

Answer 45

Repressor gens provide proteins that control the activation of structural genes, while structural genes control the activity of various metabolic activities withen a cell structure such as an enzyme.