Lecture 8- Protein Flashcards
What are the essential amino acids?
- One that the body is unable to make or can only make in inadequate quantities
- Need to be consumed from the diet
- 8-10 essential amino acids
What are non-essential amino acids?
- One that the body can make in large enough quantities
- Made from essential amino acids
- Not necessary to consume these in the diet
- 10-12 non essential amino acids
What is a conditionally essential amino acid?
• One that can become essential in certain physiologic conditions
What is an example of an conditional essential amino acid?
• Example: tyrosine becomes essential in people with phenylketonuria (PKU)
What is PKU?
- Most common inborn error in AA metabolism
- 1/12-15,000 people (mainly white and Asian populations)
- Body cannot utilize phenylalanine(EAA)
- Phe then builds up in the body as it is not metabolised
- High phe can cause neurologic damage
- Irreversible CNS damage, mental & growth retardation, seizures, small head size etc.
Unusual compounds: phenylpyruvate; phenyllactate; phenylacetate
Brain toxicity: reduced uptake of other aromatic amino acids
Tyrosine deficiency may lead to hypopigmentation
Cofactor processing can also be defective
What is this
• Normal situation
What happens in PKU?
- In PKU:
- Phenylalanine builds up
Can cause mental retardation
What is PKU prevention and treatment?
- Tyrosine must be supplied by diet • Becomes EAA for those with PKU
- Phenylalanine intake must be carefully restricted – but the amino acid is however essential for growth and development
- All infants are tested for PKU at birth
- Low protein diets (that is how you treat it)
What are the properties of amino acids?
- About 25 commonly found in dietary proteins
- Chemically diverse but have common general formula
- Mostly water soluble
- Optically active (except glycine)
- Amphoteric
- Forms cations at acid pH, anions at basic pH
- Naturally occur as L-isomers
(don’t have to memorise this so much)
What is the struture of amino acids?
• Different side chains make different amino acids
What are the essential amino acids in humans?
Essential (10)
• Phenylalanine
- Valine
- Threonine
- Tryptophan • Isoleucine
- Methionine • Histidine
- Arginine
- Leucine
- Lysine
(remember couple of each)
What are the nonessential amino acids in humans? (remember one example and what it means to be nonessential)
• Alanine
- Asparagine
- Aspartic acid
- Cysteine
- Glutaminc acid • Glutamine
- Glycine
- Proline
- Serine
- Tyrosine
What are conditionally essential amino acids in humans?
- Cysteine
- Glutamine
- Tyrosine
What is the primary structure of a protein?
• It is the sequence of amino acids that makes each protein different from the next
Dipeptide = 2 amino acids
Tripeptide = 3 amino acids
Polypeptide = many amino acids
Most proteins have many 100 amino acids
What is the secondary structure of a protein?
- Alignment of polypeptides as a right-hand alpha helix
- Stabilized by hydrogen bonds between carboxyl (C=O) and imido (NH) groups
What is the tertiary structure of the protein?
- Three dimensional folding and coiling of polypeptide into globular 3-D structure
- Caused by additional chemical interactions among side chains • Disulfide bonds
What is the quaternary structure of a protein?
• Interactive folding of several polypeptide chains together to form a “single” functional protein
- Functional proteins also might incorporate minerals or other nonprotein components
- Final shape and components determine function of protein
What is the nutritional importance of proteins?
- Nutritional value of dietary proteins is determined mainly by its primary structure (i.e., amino acid composition)
- Tertiary structure can influence protein digestibility
- Globular proteins are generally more easily digested than filamentous proteins such as collagen, elastin and keratin
What is umami?
- “fifth taste”
- Salt, sour, sweet, bitter
- Relatively new discovery (confirmation, ~ year 2000)
- Cured meats, cheese, soy, miso, Worcestershire sauce, vegemite, kimchee
- Attractive taste to humans
- Monosodium glutamate MSG
- Free glutamate
- Marker of nutrient (protein) rich food?
What do you need to synthesise protein?
• Protein synthesis cannot proceed without an adequate supply of all amino acids, which contribute to the primary structure of that protein
What is the biological value of a protein?
• The ability of a specific dietary protein to supply amino acids in the relative amounts required for protein synthesis by body tissues is defined as biological value
- Influenced mainly by essential amino acid composition
- Is not fixed, but varies with the needs of different species, physiological and nutritional states
What are the biological functions of proteins?
Principal organic chemical constituents of body organs and soft tissues
Enormous functional diversity
- Cell membrane structure and function
- Enzymes
- Hormones and other chemical messengers
Immune factors (antibodies)
Fluid balance
Acid-base balance
Transport
Source of energy and glucose
How is protein important mechanically and structurally?
- Collagen
- Bone and skin
- Keratin
- Hair and nails
- Motor proteins
- Make muscles work!
How are proteins important as enzymes?
- Proteins that catalyze (speed up) chemical reactions without being used up or destroyed in the process.
- Anabolic (putting things together) and catabolic (breaking things down) functions.
- Examples
- Digestion
- Salivary amylase
- Trypsin
How do proteins act as hormones?
- Chemical messengers that are made in one part of the body but act on cells in other parts of the body.
- Peptide hormones are synthesized in the same steps as normal protein manufacture.
- Examples
- Insulin
- CCK
- Some reproductive hormones
How are proteins important in immune function?
• Antibodies are proteins that attack and inactivate bacteria and viruses that cause infection
How are proteins important for fluid balance?
- Proteins in the blood help maintain appropriate fluid levels in the vascular system.
- Fluid is forced into tissue spaces by blood pressure generated by pumping action of the heart.
- Fluid returns to blood because of “osmotic pressure.”
How are proteins important as transport proteins?
- Transport substances in the blood
- Lipoproteins (transport lipids)
- Hemoglobin (transports oxygen and carbon dioxide)
• Transport materials across cell membranes.
How are proteins important as source of energy?
- Proteins are the last to be used for energy!
- Occurs in starvation and low carbohydrate diets
- When excess protein occurs…
- Some amino acids converted to glucose which is converted to fat.
