UNIT 3 - AOS 1 - CH 1.7 -> 1.9 - Amino acids & Polypeptides, Proteome, Protein secretory

Question 1

Polymer

Answer 1

Protein (polypeptide)

Question 2

Monomer

Answer 2

Amino acids

Question 3

Structure of an amino acid

Answer 3

LEFT:
Amino Group (H2N)

TOP:
Variable Group (R)
(R = what changes between each amino acid)

BOTTOM:
Hydrogen (H)

RIGHT:
Carboxyl group (COOH)

Question 4

Property groups of amino acids

Answer 4

• Hydrophilic
• Hydrophobic
• Positively charged
• Negatively charged
• Hydrophobic & aromatic (neutral)

Question 5

Structure of polypeptide chain (how amino acids bond)

Answer 5

• Amino group of one amino acid bonds with carboxyl group of next amino acid = Peptide bond (CONH)
• Requires energy for the condensation reaction (removal of water molecule for each peptide bond)

Question 6

Hierarchical structure

Answer 6

Different proteins form different shapes = different functions
- Dependent on amino acid sequence

• Primary
• Secondary
• Tertiary
• Quaternary

Question 7

Primary Structure

Answer 7

Specific linear sequence of amino acids in the polypeptide chain which is determined by the DNA sequence

Question 8

Secondary Structure

Answer 8

The folding of some portions of the amino acid sequence using hydrogen bonds to help stabilise 3D shape.

1. Alpha helix
2. Beta-pleated sheet
3. Random coil

Question 9

Tertiary Structure

Answer 9

• Irregular 3D folding of the whole (now)polypeptide chain & dependent on primary and secondary structures.
• Shape is critical for function
• Some proteins are functional at this stage but most are non-functional polypeptide chains in this stage.

Question 10

Forces that maintain tertiary structure of protein

Answer 10

• Hydrogen bonds
• Ionic attractions between charged R groups (e.g., + & -)
• Interactions between hydrophobic R groups in protein interior
• Covalent disulfide cross links
  . Strongest bond
  . Occurs only between two cysteine amino acids between sulfur in their R groups

Question 11

Quaternary structure

Answer 11

2 or more non-functional polypeptide chains interact to form a functional protein.

Question 12

Function of most proteins

Answer 12

Controlling metabolic pathways (anabolic and catabolic reactions)

Question 13

Examples of proteins and their function

Answer 13

STRUCTURAL:
Fibrous support tissue in skin, bone, tendons, blood vessels etc.

ENZYME:
Catalyse reactions (e.g., ATP synthase)

CONTRACTILE:
Muscle movement (e.g., myosin and actin filaments)

IMUNOGLOBULIN:
Defence body activity (e.g., antibodies)

HORMONE:
Regulate body activity (e.g., insulin, growth hormones)

RECEPTOR:
Respond to stimuli (e.g., insulin receptors)

TRANSPORT:
Carry other molecules (e.g., haemoglobin)

Question 14

Enzymes as catalysts (catalyst def)

Answer 14

Catalysts: Speed up the rate of reaction without being used in the reaction.

• ^ heat = ^ energy

Question 15

Proteome definition & 1 key point

Answer 15

“All proteins involved in chemical reactions, that are produced by a single cell in a particular environment”

Study of proteomes = proteomics

Proteins don’t act in isolation -> but together in regulatory pathways

Question 16

Questions when exploring various aspects of proteome

Answer 16

• Differences and similarities ? (Look and function)
• What is proteome profile of diseased tissue / fluids surrounding tissue?
• In what ways do they differ from the healthy state

Question 17

the role of rough ER in export of proteins

Answer 17

• proteins intended for export from the cell are synthesised at ribosomes attached to the rough endoplasmic reticulum
• from there, proteins move though channel network (lumen) of the RER towards the Golgi Apparatus. (polypeptide chain inserted into linen of RER pores)

Question 18

2 types of ribosomes

Answer 18

1. FREE FLOATING RIBOSOMES:
   Proteins are used in the crisply of the cell

2.MEMBRANE BOUND RIBOSOMES:
Ribosomes bound to RER, produce proteins that need to be distributed to membrane bound organelles or exported from the cell.

Question 19

structure and function of Golgi Apparatus

Answer 19

• stack of 4-8 flattened membrane sacs (cisternae)

Function:
Modify and package proteins for export from the cell.

Question 20

steps of the role of the Golgi Apparatus in export of proteins

Answer 20

STEP ONE:
Proteins are delivered to the sis cos side of the golgi apparatus from the RER

STEP TWO:
As the proteins move through they are modified by resident enzymes
- either add/remove sugars or add phosphate/sulphur groups
- occurs in the cis, medial and trans compartments

STEP THREE:
Modifications are necessary to target the proteins into there needed destination (like shipping labels )

Question 21

Role of vesicles in the export of proteins

Answer 21

STEP ONE:
Vesicles bud off from the transface with ‘cargo proteins’ binding to specific membrane-bound receptor & creates “shipping label” for vesicles.

STEP TWO:
The vesicles that bud off from the golgi apparatus diffuse to their target location over very short distances. Over long distances -> carried by motor proteins along the microtubules of the cytoskeleton -> then exocytosis.