Protein Flashcards
(45 cards)
What is Protein?
- Linear chains of amino acids – polypeptides
- Protein = proteos meaning “primary” or “taking first place”
- Not a single entity but a complex mix of many different proteins –
each with its own amino acid composition & sequence - A single protein can have from 50 to 1000 amino acids
- The particular sequence of amino acids confers varying roles &
functions for different amino acids
Essential (indispensible) aa
not synthesized by mammals and are therefore dietarily essential or indispensable nutrients
1. Isoleucine
2. Leucine
3. Valine
4. Lysine
5. Methionine
6. Phenylalanine
7. Threonine
8. Tryptophan
9. Histidine
Amino Acids can be grouped on the basis of:
- Side chain structure
E.g. Aromatic, acid, basic, sulfur containing etc. - Net electrical charge
Neutral, positively charged, negatively charged - Polarity
Polar (interact with water) and non-polar - Essentiality
conditionally essential (indispensible) aa
usually not essential, except in times of illness and stress
1. Arginine
2. Cysteine
3. Glutamine
4. Proline
5. Tyrosine
Non-essential (dispensible) aa
- Alanine
- Aspartic acid*
- Asparagine
- Glutamic
Acid† - Glycine
- Serine
Protein Digestion occurs where?
stomach
* HCL denatures proteins
* HCL converts pepsinogen to pepsin
* Pepsin acts on protein→ large polypeptides
small intestine
Pancreas
- Secretes zymogens (proenzymes) which are activated in the SI to
* Trypsin
* Chymotrypsin
* Carboxypeptidases A & B
Enterocytes
- Secrete
* Aminopeptidases
* Dipeptidyl amino peptidases
* Tripeptidases
Attack specific bonds → smaller polypeptides →
amino acids, dipeptides, tripeptides
no digestion in oral cavity
Protein Absorption
- where?
- uses?
- dependent on?
- absorbed through?
- also needs a ______ system
- Occurs in the Small Intestine, especially duodenum
and upper jejunum - Uses energy
- Specific transport systems, mainly Na dependent
- Absorbed through brush border into enterocyte
- Then absorbed through basolateral membrane of
enterocyte by transport systems and taken into
circulation for distribution around the body - Absorption in the body systems also needs a carrier
system
Protein Absorption
- capacity
- peptides have their own _______
- which aa are absorbed more easily?
- supplements with high amounts of one aa may?
- Capacity for absorption is much greater than dietary intake as the body
secretes protein into the bowel ~ 70 – 300g/day - Peptides have their own transporters and are absorbed more quickly than
amino acids - Essential amino acids are absorbed more quickly than non-essential amino
acids - Supplements with high amounts of one amino acid may impair absorption
of others with the same carrier
Protein Synthesis
- increases in tissues following _______?
- fast proteins
- slow proteins
- All AAs needed to synthesise a particular ___?
- Synthesis of a particular protein in the body involves transcription of a ____ into _____ followed by its ________-
- Increases in tissues following food intake
- Amino acid use in the body influenced by the type of dietary proteins
- Fast proteins – whey, soy, amino acid mixtures, protein hydrolysates
- Slow proteins - casein
- Slow – lower and prolonged blood amino acid [ ] and better retention than fast, used more for skeletal muscle
- All AAs needed to synthesise a particular P must be available at point of synthesis
- Synthesis of a particular protein in the body involves transcription of a gene into mRNA followed by its translation
Hormones with a role in protein synthesis
- Protein degradation predominates over synthesis
- Epinephrine
- Cortisol
- Higher glucagon:insulin
e.g. Overnight, fasting, infection, injury, trauma - Protein synthesis predominates over degradation
- Higher insulin:glucagon
- Growth hormone
e.g. after eating, greatest if CHO & protein eaten together
Protein (P) Content in the Body
- Protein content per 60-70 kg adult
- aa pool
- only a small ______ protein store or buffer (_% total body protein) with no energy storage form of protein
Protein content per 60-70 kg adult:
* 10-11kg P i.e. ~16% body weight
* muscle ~43%
* Organs ~25%
* skin ~15%
* blood ~16%
* amino acid (AA) pool
* small pool of free AAs in all tissues
* supplies AAs for P formation
* receives AAs from P degradation
* only a small ‘labile’ protein store or buffer (1% total body
protein) with no energy storage form of protein
Structural role of protein
- Contractile proteins – actin + myosin
- Cardiac, skeletal and smooth muscle
- Fibrous proteins
- Collagen, elastin and keratin
- Bone, teeth, skin, hair, tendons, cartilage, blood vessels, hair and
nails
buffering role of protein
- Proteins contribute to acid base balance by accepting/releasing H+ ions
- Works with the phosphate system (in cells) and bicarbonate system (in
blood) to maintain pH
fluid balance role of protein
- Attract and keep water in a particular location by contributing to osmotic pressure
- Imbalance contributes to oedema or ascites
catalyst role of protein
- Enzymes
- Bind with substrate to generate a product
- Often require a cofactor or coenzyme
- Multiple physiological processes depend
on enzymes
messenger role of protein
- Hormones – chemical messengers in the body
- Synthesized and secreted by endocrine organs
- Transported in blood to other locations where
they bind with protein receptors
immunoprotection role of protein
- Immunoproteins – immunoglobulin (Ig) or antibodies (Ab)
- Produced by plasma cells from B-lymphocytes
- Bind and inactivate antigens
- Immunoprotein-antigen complex destroyed by
complement proteins or cytokines
transport role of protein
- Transport various substances in
the blood, into, out of or within
cells - Cell Membranes
- Uniporters, symporters and
antiporters - Blood
- 100s
- Lipoproteins
- Albumin
- Transthyretin/ Prealbumin
- Retinol binding protein
- Globulins
acute phase responder role of protein
- Synthesised in the liver in
response to a sudden critical
illness – infection, injury or
inflammation - E.g. C-reactive protein
This Photo by Unknown Author is licensed under CC BY-SA
N-Containing Nonprotein Compounds
- Glutathione
- Antioxidant
- Transports amino acids in some tissues
- Participates in synthesis of leukotrienes
- Carnitine
- Transports fatty acids across the inner
mitochondrial membrane for oxidation - Role in ketone catabolism for energy
- Creatine
- Component of creatine phosphate
(phosphocreatine) - Source of energy for the muscle
- Purine and Pyrimidine Bases
- Components of DNA and RNA
Protein turnover
All body proteins are in ‘dynamic state’ i.e. constant synthesis & degradation
* absolute rates vary in different tissues (minutes, months)
enzymes, skin or mucosa, structural proteins (bone, muscle)
* relative rates are determined by N balance experiments
in adults: synthesis = degradation → N balance
* synthesis: ~4 g P/ kg body weight/ day
in children: synth > degradation → +ve N balance
* ~12 g P/ kg bw /d in newborn
* ~6 g P/kg bw /d by 1 year
Nitrogen balance is a measure of the _____ ________ status of a person - _____ vs _______
- it refers to overall relationship between _ intake (diet) & _____
- N is mainly derived from _____ __ (NH2 group) but also other compounds e.g. _____ ____, _______ from meat, ________
- N balance reflects _______ not absolute rates of protein synthesis
versus degradation
- protein nutritional and anabolic
vs catabolic - N and excretion
- protein N and nucleic acids, creatine from meat, vitamins
- relative
Factors affecting N balance:
Positive balance
Physiological state
* Growth
* Pregnancy
* Muscle building
* Intense physical activity
* Convalescence
Nutritional state
* incr. in E intake with weight gain
* switch from low to high P intake
Factors affecting N balance:
Negative balance
Physiological state
* injury, surgery
* burns
* bleeding
* proteinuria
* diarrhoea
Nutritional state:
* not enough E
* not enough P
* switch from high to low P diet
