Protein - Protein Functions:

Question 1

Protein Functions:

Answer 1

Each protein has a specific function that is determined during protein synthesis.

Functions include:
* Structure of body tissues, e.g. Collagen.
* Movement e.g. Actin and myosin fibres (in muscles).
* Carrier molecules, e.g. Haemoglobin.
* Storage molecule, e.g. Ferritin (iron).
* Fluid balance in the blood, e.g. Albumin.
* Enzymes (for reactions in the body).
* Hormones (e.g. Insulin) and cell membranes.
* Immune function, e.g. Antibodies.
* Clotting mechanisms, e.g. clotting factors.
* Alternative energy source.

Question 2

Growth and Maintenance

Answer 2

• Proteins are the building blocks of muscles, blood, skin, and most body structures.
• Bones are formed of a collagen matrix, which provides a framework for minerals to deposit on.
• Actin and myosin filaments involved in muscle contraction are also proteins.
• Collagen provides building material for ligaments, tendons, blood vessel walls, dermis, etc.
• Proteins are also needed for the replacement of cells, e.g. of skin, GIT cells etc.

Question 3

Hormones and Receptors

Answer 3

Some hormones are derived from cholesterol, whilst others are made from amino acids. These include:
* Tyrosine + Iodine = thyroid hormones. For example: Iodine (e.g. seaweed) and tyrosine (e.g. fish) supports thyroid hormone production.
* Tyrosine = dopamine, norepinephrine, epinephrine (and neurotransmitters).
* Tryptophan = serotonin, melatonin (and neurotransmitters).
* Two polypeptide chains = insulin.
* -One polypeptide chain = glucagon, PTH, calcitonin.
* *Cell membrane proteins are receptors for hormones

Question 4

Enzymes

Answer 4

Enzymes are proteins that speed up biological reactions. For example, the digestive enzyme ‘amylase’ digests starch.

Question 5

Immunoglobulins (or Antibodies)

Answer 5

Immunoglobulins are proteins found in blood and bodily fluids.
* They are used by the immune system to identify and neutralise foreign materials such as bacteria and viruses.
o IgG is the most abundant antibody in the blood (detects viruses, bacteria, fungus and destroys or neutralises them)
o IgA is found in bodily secretions (e.g. tears, saliva, mucus, sweat). (Gatekeeper – detects pathogens before entering the body)
o IgM is the first antibody to appear in response to antigen exposure
o IgE release is associated with allergic reactions and parasites.

Question 6

Transport

Answer 6

• Some proteins combine with other substances in the blood or within cells to provide a mode of transport. Insufficient transport of vital nutrients and products will negatively impact health.
• For example;
  o Albumin can bind to calcium, zinc and B6, as well as steroids and fatty acids.
  o Transferrin’s bind to iron.
  o Ceruloplasmin binds to copper.
  o Haemoglobin transports oxygen in the blood.
• Note: Protein malnutrition, hypochlorhydria (low stomach acid) or liver dysfunction can be the cause of low serum albumin.

Question 7

Buffers

Answer 7

• Some amino acids have side chains (R-groups) that can easily pick up or let go of hydrogen ions (H+), helping to regulate the acid-base balance in body fluids.
• Proteins that contain a lot of these amino acids therefore make good buffers, helping to keep the acid-base balance of body fluids such as the blood.
  o The amino acid histidine is the best buffer at our healthy physiological pH range (7.35 –7.45).
  o Another amino acid, cysteine can also act as a buffer within the normal human pH.

Question 8

Fluid Balance

Answer 8

• Proteins attract water. This osmotic pressure from proteins (i.e. albumin) in fluid is called ‘oncotic pressure’.
• If protein levels fall too low, water leaks out of the blood vessels and accumulates in interstitial spaces = oedema.
• Protein-related causes of oedema include:
  o Excessive protein losses due to kidney disease.
  o Inadequate protein synthesis due to liver disease.
  o Inadequate dietary intake of protein (malnutrition). This explains the appearance of ascites (a distended, fluid-filled abdomen) in the world’s poorest countries.
  Oncotic = water (osmotic) pressure exerted by proteins

Question 9

Glycoproteins:

Answer 9

• Mucins – found in mucus and saliva; provide a protective, lubricating barrier.
• ABO blood (type) antigens.
• Hormones – incl:
  o Luteinising Hormone (LH)
  o Follicle Stimulating Hormone (FSH)
  o Thyroid Stimulating Hormone (TSH)
• Major Histocompatibility Complex – cell surface receptors involved in adaptive immunity (e.g. antigen presentation).
• Proteoglycans (a subclass of glycoprotein) are bound to glycosaminoglycans (GAGs) and found in the extracellular matrix e.g. chondroitin sulphate, found in cartilage – shock absorbs.