Protein Flashcards
What determines AA chemical and physical structure
AA side chain (r group)
What determines the structure and function of a protein
AA composition
What determines the 3D nature of a protein?
AA sequence
Where does protein digestion begin
Stomach
Stomach digestion (5)
HCL rich fluid is secreted from parietal cells
Protein is denatured by low pH
Inactive form of pepsin (pepsinogen) is secreted
HCL activates pepsin
Pepsin cleaves proteins into smaller peptides
What is protein denaturation (2)
When protein straighten and uncoils
Thus allowing greater access to proteolytic enzymes
Small intestine digestion (5)
Partially broken down protein enter small intestine
Protein exposed to proteolytic enzymes
Pancreas produces proteolytic enzymes in zymogen form
Produces AAs and oligopeptides
Membrane bound enzymes further break down peptides
Absorption (2)
Digested products (dipeptides, tripeptides and AAs) are absorbed into epithelial cells They then pass in capillaries and circulate blood
Which AAs are oxidised to provide energy for intestinal walls (3)
Glutamine
Aspartate
Glutamate
What do AAs consist of?(4)
Central carbon bound to hydrogen
Amino group (NH3)
Carboxylic group (COOH)
R group - amino acid side chain
What type of reaction forms a peptide bond?
Dehydration synthesis (release H20 + requires energy)
One hydrogen and oxygen from carboxyl group
One hydrogen from amino group
Describe the primary protein structure (3)
AA sequence
R groups of adjacent AA located on opposite side of the AA chain
No interactions between r groups
Describe secondary structure (2)
Determined by the number and sequence of AA
Chemical interactions among the AAs begin forming the primary structure
Tertiary structure (2)
3D shape occurs
Interactions among side chains a considerable distance from each other a long chain
Quaternary structure (2)
2 or more polypeptide chains interact
To form functional entities
What supplies the AA pool?(3)
Diet
De Nono synthesis
Protein degradation
What causes AA pool demand?(3)
Oxidation
Other pathways (e.g. gluconeogenesis)
Protein synthesis
What processes make proteins in the body?
Transcription and translation
_____ AAs must be available for optimal protein synthesis to occur?
All
How much does AA oxidation contribute to oxidative metabolism of the body?
10-20%
What is ammonia?(2)
Potent neurotoxin
Disposal is crucial for survival
Ammonia excretion (3)
Transported to the liver
Enters urea cycle
Urea is excreted by kidneys
What is an oxoacid?
Carbon skeleton of the AA
What is transamination?(2)
Amino group is transferred via an enzyme to an oxoacid to form a new AA
Used to synthesis non-essential AAs
What is the transaminate enzyme?(2)
Pyridoxal phosphate (PLP) Which is a derivative from vitamin B6
Protein is the ____ most abundant chemical in the body
Second
Approx how many proteins are encoded by the genome?
35000
Which 4 protein makes up half of the total protein in human body?
Collagen (25%)
Haemoglobin
Myosin
Actin
What is protein?
Polymers of AAs joined together by peptide bonds
Essentials AAs (3)
Can not be produced endogenously
Must be provided in diet
9 of them
Non essential AAs (3)
Can be produced endogenously
By transamination of carbon skeleton
Relies on the availability of precursors
Conditionally essential AAs (2)
Rate of endogenous production is not sufficient under certain circumstances
Therefore it becomes essential
What is pepsin?(3)
Proteolytic enzyme
Cleaves proteins into smaller peptides
Inactive form is pepsinogen
Pancreatic enzymes in zymogen form secreted by pancreas (3)
Tripsinogen
Chymotryosinogen
Procarboxypeptidase A+B
Activated pancreatic proteolytic enzymes (3)
Trypsin
Chymotrypsin
Carboxypeptidase A+B
What is zymogen form (2)
Inactive enzyme precursors
Requires a biochemical change to activates e.g hydrolysis
Define proteolysis
Breakdown of proteins by the proteolytic enzymes (hydrolysis)
How are AAs oxidised?
By deamination
Explain the deamination process (2)
Amino group is removed from the amino acid
The products are an oxo-acid and ammonia
What determines the use carbon skeletons
The AA it was derived from
How are oxoacid used in energy production?(3)
Converted into either:
Pyruvate
Alpha-ketoglutarate (TCA intermediate)
Oxoloacetate (TCA intermediate)
What are the two key types of oxoacid?
Glucogenic
Ketogenic
What are ketoacids?(4)
AA derivatives that yield acetyl CoA or acetoacetate
Used as precursors for FA synthesis
Or oxidised as metabolic fuel
Cannot be used in gluconeogenesis
What are glucogenic oxoacids?
Used as intermediates for gluconeogenesis
How are AAs supplied by de novo synthesis?
Transamination
Nitrogen constitutes _____ of most proteins
16%
What are the major determinants of nutritional quality of food proteins?(2)
Content of essential AAs
Digestibility of the food source
What are complete proteins foods?
Protein sources that contain all essential AAs in quantities sufficient for human requirements
Examples of complete protein foods (4)
Poultry
Fish
Eggs
Dairy
What are incomplete protein foods?
Protein sources that lack one or more essential AA
Examples of incomplete protein foods?(3)
Plant sources
Corn
Legumes
Why is plant protein less digestible than animal protein sources?(2)
Restriction of digestion by plant cell walls
Presence of anti-nutritional factors
Examples of anti-nutritional factors (3)
Amylase
Trypsin inhibitors
Tannins
Digestibility of animal proteins
90-95%
Digestibility of plant proteins
60-80%
Digestibility of soy
90%
Protein loss in malnutrition (3)
Some tissue can only metabolise glucose
Protein must be degraded to provide AAs for gluconeogenesis
Lead to muscle wasting
Nitrogen balance (3)
Method used to calculate dietary protein requirement
Measures dietary intake of nitrogenous compounds
And excretion of nitrogen
Essential AAs examples
…
What is the optimal pH for pepsin activity?
2
pH that reduces pepsin activity
5
What is required for protein synthesis to occur
All AAs
