Lecture 7: Proteins Flashcards
What type of proteins are involved in structural roles?
Collagen/Keratin
What is the structural roles of collagen and keratin?
Bone, skin, hair, nails, tendons, ligaments
What type of proteins are involved in contraction?
Actin and myosin
What is the structural roles on actin and myosin?
Contractile proteins
What type of proteins are involved in transport?
Hemoglobin, cytochromes and lipoproteins
What are the transport roles of hemoglobin, cytochromes and lipoproteins?
O2 and CO2 transport, ETC and lipids
What type of proteins are involved in metabolic regulation?
Enzymes and hormones
What are the metabolic regulation roles of enzymes and hormones?
Nutrient anabolism and catabolism
What type of proteins are involved in immune function?
Antibodies
What are the immune function roles of antibodies?
Eliminates foreign pathogens
What is low muscle mass associated with?
Has been associated with increased morbidity, poorer quality of life and higher mortality
What is low muscle strength shown to be a significant and independent predictor of?
Mortality risk
What is the composition of amino acids?
Amino acids contain carbon, hydrogen and oxygen and contain nitrogen
What is the composition of CHO and Fat?
Carbon, hydrogen and oxygen - not nitrogen
What is the structure of Amino Acids?
A carboxyl group, amine group and variable side chain
How do amino acids differ from each other?
Each AA has a different side chain
How many amino acids are there?
20
What are the 2 categories of amino acids?
Essential and non-essential
What are essential amino acids?
cannot be synthesised by the body and therefore must be consumed in the diets
What are non-essential amino acids?
can be synthesised from other amino acids via transamination
What is transamination?
a biochemical process in which an amino group from one amino acid is transferred to a keto acid (α-keto acid), forming a new amino acid and a new keto acid
What essential amino acids are involved in muscle synthesis?
Isoleucine and Leucine (BCAA)
What essential amino acid is involved in the blood brain barrier?
Valine (BCAA)
What is a BCAA?
Branched chain amino acid
What is a dipeptide?
Composed of a 2 AA that are joined by a chemical bond, known as a peptide bond
What is a polypeptide?
Longer chains of AA are known as polypeptides (>20 AA)
What do proteins consist of?
Many polypeptide chains
What is a primary structure?
the linear sequence of amino acids in a polypeptide chain
What are primary structures determined by?
the AA sequence
What is a secondary structure?
refers to the local folding of the polypeptide chain into specific shapes stabilised by hydrogen bonds.
What are secondary structures determined by?
the interactions between groups (short)
What is a tertiary structure?
overall three-dimensional shape formed by the folding and interactions of its secondary structural elements
What is a tertiary structure determined by?
interactions between side chains (3D)
Where does protein digestion begin?
In the stomach
After the stomach where is the next stage of digestion?
The pancreas
After the pancreas where is the next stage of digestion?
The small intestine
How are proteins are digested in the stomach?
Hydrochloric acid denatures the proteins and pepsin degrades proteins to large polypeptides and AA
How are proteins digested in the pancreas (arriving as polypeptides and AA)?
Pancreatic enzymes include trypsin and chylotrypsin degrade polypeptides to oligopeptides and AA
How are proteins digested in the small intestine (arriving as oligopeptides and AA)?
Aminopeptidase degrades oligopeptides to peptides and AA
How do peptides and AA’s enter the circulation from the small intestine?
AA and small peptides are transported across the intestinal membrane. Peptides are hydrolysed in the cytosol and thus AA enter the circulation
Can we store excess AA in the body?
No we cannot
What represents the AA pool?
The AA in the blood and ECF
How much does protein turnover contribute to BMR?
Contributes approx. 20% to BMR
Which organ plays a critical role in regulating the composition of the AA pool?
The liver
Where are amino acids found in the body?
ECF, blood, liver and muscle
Where can AA be released from?
liver and muscle
What happens in both the liver and muscle?
Proteins are degraded and synthesised
What does muscle maintenance mean?
Muscle protein synthesis = muscle protein breakdown
What does muscle gain look like?
Muscle protein synthesis > muscle protein breakdown
What is MPS?
Muscle protein synthesis
How does MPS vary?
Varies between different dietary protein sources
What does MPS depend on?
depends on post-prandial rise in plasma essential amino acid concentrations (especially leucine)
What is leucine?
an essential amino acid
What provides the necessary precursors for protein synthesis rates to increase?
Plasma amino acid concentrations
What are examples of high protein meats?
Lean mince, sirloin steak, chicken and salmon
What are high protein foods that are not meat?
Peanut butter, almonds, tofu, eggs
What does protein quality refer to?
How many of the essential AA’s they contain and what concentration of essential AA they contain
What are complete proteins?
All EAA present (generally animal proteins)
What are incomplete proteins?
plant proteins are deficient in one EAA (lysine, tryptophan, methionine) - generally plant proteins
What are limiting AA’s?
the amino acid that is missing from an incomplete protein
What is the problem with protein quality in vegetarians?
Poor digestibility - cell walls of plant proteins inhibit digestion, anti-nutritional factors inhibit digestion
How is problems with protein quality in vegetarians/vegans overcome?
By consuming a combination of plant proteins
What is PDCAAS?
Protein digestibility-corrected amino acid score
What is DIAAS?
Digestible indispensable amino acid score (DIAAS)
What is protein quality often based on?
PDCAAS or DIAAS
What is food protein quality traditionally dependent on?
its amino acid content and the availability of these amino acids in circulation, factors that would influence their metabolism within different body protein pools
Which absorbs faster, plant-based or animal-based proteins?
Plant-based whole foods have a lower absorbability
What percent of the protein in eggs and chicken is absorbed?
85-95%
What percent of the protein in chickpeas, mung beans and peas are absorbed?
50-75%
Why do plant-based proteins have a lower absorbability?
There are anti-nutritional factors in plant-based protein sources e.g. fibre and polyphenolic tannins attenuate absorption
Which has been shown to be more effective, whey or soy?
Whey protein
Which has been found to increase muscle protein synthesis more, wheat or whey?
Wheat
How much whey protein strongly increases muscle protein synthesis rates?
20-25g (providing 2.2-2.7g leucine)
What quantities of food provide 2.7g leucine?
33g potato, 37g brown rice, 38g pea, 40g soy, 45g wheat protein
Which has more leucine content, animal or plant proteins?
As a general rule, the leucine content of animal proteins (8-13%) exceeds plant proteins (6-8%)
Animal protein vs Plant protein
Animal protein has a higher protein quality, is usually considered to be superior to plant protein for building muscle mass
What is the protein intake recommendations for recreational athletes?
0.8-1.0g/kg/d
What is the protein intake recommendations for elite male endurance athletes?
1.6g/kg/d
What does current evidence suggest for protein intake to maximise protein synthesis?
0.3-0.4g per kg of body mass when consumed with food
How is protein synthesis optimised across the day?
Protein synthesis is highest when consuming 20-30g of protein over 3-4 feedings per day
How is protein involved in recovery?
Eating a source of high quality protein soon after exercise will promote muscle protein synthesis
How much protein is recommended to repair during recovery?
0.25-0.30g/kg BM
What is the rate of absorption of PRO, CHO, and Fat?
PRO = approx. 2-10g/h
CHO = 60-100g/h
Fat = 14g/h
What is the absorption rate of soy protein isolate?
3.9g/h
What is the absorption rate of casein isolate?
6.1g/h
What is the absorption rate of whey isolate?
8-10g/h
What is the LAA in soy?
Methionine
What is the LAA in corn?
Tryptophan, Methionine and Cysteine
What is the LAA in rice and wheat?
Lysine
What is leucine sensed by?
senstrin2
What does senstrin2 promote?
translocation of mammalian target of rapamycin complex 1 (mTORC1) to the lysosome membrane where it becomes activated
What happens when mTORC1 is activated?
Results in the activation of the downstream anabolic signalling pathways that control muscle tissue protein synthesis
What are AA’s in the liver deaminated into?
Urea and carbon skeletons
What are the essential amino acids?
Isoleucine (BCAA)
Leucine (BCAA)
Valine (BCAA)
Lysine
Methionine
Phenylalanine
Threonine
Trytophan
