Protein Metabolism Flashcards
(90 cards)
1
Q
What are the 7 types of protein based on function?
A
Structural, contractile, transport, storage, hormonal, enzyme, protection
2
Q
What is the function of structural proteins?
A
Found in tendons, cartilage, hair and nails
3
Q
Give examples of storage proteins
A
Milk proteins
4
Q
What do hormonal proteins do?
A
Act as signalling molecules like insulin and growth hormone
5
Q
What function do protection proteins serve?
A
Immune response
6
Q
What’s the most abundant gas in the atmosphere?
A
Nitrogen - 78%
7
Q
Describe the nitrogen cycle relevant to protein metabolism
A
- Nitrogen gas fixed by bacteria
- Plants incorporate it into proteins
- Animals eat plants to gain the protein from it
8
Q
What are proteins made of?
A
Polymers of amino acids bonded via peptide bonds
9
Q
How many standard amino acids are there?
A
20 standard or canonical amino acids encoded by universal genetic code
10
Q
What are the three key chemical groups in an amino acid?
A
Central ‘alpha’ carbon, amino group (basic), carboxyl group (acidic) and variable side chain
11
Q
What does the side chain in an amino acid determine?
A
The function and properties of the amino acid
- different for each amino acid
12
Q
Name some amino acids not found in large amounts in food but present in the body
A
Gamma Amino Butyric Acid (GABA) and Beta alanine
13
Q
What’s the role of GABA amino acid?
A
CNS inhibitory neurotransmitter
14
Q
What is the role of Beta alanine?
A
Used in carnosine synthesis for intracellular buffering of hydrogen ions
15
Q
How are amino acids classified based on essentiality?
A
Essential, non-essential, conditionally essential
16
Q
What are essential amino acids?
A
Cannot be synthesised by the body and must be obtained from the diet
17
Q
What are non-essential amino acids?
A
Synthesised by body cells in sufficient amounts
18
Q
What are conditionally essential amino acids + give an example?
A
Made by the body but only in certain conditions and must be supplied by diet if demand is high
- arginine during periods of rapid growth (childhood)
19
Q
How are proteins formed from amino acids?
A
By condensation reactions where carboxylic and amino groups join, liberating water and forming peptide bonds
20
Q
What is the primary structure of a protein?
A
The sequence of amino acids which determines its functional properties
21
Q
How does exercise affect proteins?
A
It can drive degradation and synthesis of specific proteins beneficial for that exercise
22
Q
What happens to haemoglobin concentration when iron stores are low + why?
A
Haemoglobin concentration drops
- haemoglobin is the last storage of iron to be depleted = good indicator if someone is iron deficient (anaemia)
23
Q
How can haemoglobin concentration be measured?
A
Via capillary blood sample
24
Q
What happens to dietary protein after ingestion?
A
- Digested by protease enzymes in the gut
- into amino acids and dipeptides
- These are absorbed through the small intestine wall into the bloodstream
- Then transported to body cells
- Used to make new body protein
25
Can peptides be absorbed through the intestine wall?
Some belief that di- and tri-peptides may cross enterocytes and reach the bloodstream with possible bioactive properties
- e.g. peptides from milk
26
What are common sources of protein + any emerging ones?
- Animal (meat, fish, cheese, eggs)
- Vegetable (cereals, nuts, potatoes, legumes)
- Mycoprotein (fungal e.g. Quorn)
- Insects
27
Why is protein considered costly?
Most expensive part of shopping for consumers and has high planetary impact
28
What determines protein quality?
- Essential amino acid content
- Bioavailability (digestibility and losses) of protein
- Presence of anti-nutritive factors
29
How does essential amino acid content determine protein quality?
Higher content of essential amino acids = increased quality of protein
30
What happens to excess AAs?
Used for energy production and not protein synthesis
31
What does bioavailability of protein refer to?
Amount lost in digestion, absorption + metabolism etc
32
How digestible are different protein sources?
- Animal protein >90%
- Legumes ~80%
- Plant protein 60-90%
33
What are anti-nutritive factors and their impact?
1. Protease inhibitors and lectins inhibit digestion and can cause GI inflammation
- Heat treatment can inactivate these substances so they are good for us
34
What is mutual supplementation?
Combining different protein sources to provide complete essential amino acid intake
35
What individuals is mutual supplementation important for?
Vegetarians and vegans
- often consume lower quality proteins
- less of a worry for those who eat animal proteins
36
What does a lack of essential AAs lead to?
Poorer recovery
37
What are dispensable amino acids?
Non-essential amino acids that can be manufactured in the body
38
What is transamination?
Transfer of an amine group from one amino acid to a keto acid to create non-essential amino acids from essential ones
39
What catalyses transamination?
Transaminases which require pyridoxal phosphate (PLP), a co-enzyme derived from vitamin B6
40
How does amino acid catabolism contribute to energy production?
1. Amino acids are oxidised for energy
2. Lose nitrogen via urine
41
How is nitrogen removed from amino acids for ATP production?
- Nitrogen is removd by transamination = urea
- While the carbon skeleton enters metabolism pathways like the Krebs cycle to produce ATP
42
What role does alanine play in amino acid metabolism?
Alanine transports nitrogen from muscle to liver for removal
- all amino acids provide energy expect this one
43
What happens in the liver after nitrogen removal from AA?
- Liver removes nitrogen = urea formation, preventing ammonia toxicity
- Urea enters blood and is filtered by kidneys
- Gluconeogenesis occurs
44
Why is gluconeogenesis important after amino acid catabolism?
It produces blood glucose used mainly by the brain
45
How much protein is in the body of a 70kg male?
Around 12kg of protein including 7kg in skeletal muscle and 200g of free amino acids
46
Why is muscle mass greater than its protein content?
Because muscle is made up of 75 to 80% water and only around 20% protein
47
What is protein turnover?
The continual synthesis and breakdown of muscle protein and amino acids
48
What happens to skeletal muscle mass in sedentary individuals?
It remains relatively stable with ongoing protein synthesis and degradation
49
Do all body proteins turnover at the same rate?
No bone tissue turns over slowly whereas tissues like the stomach turn over quickly
50
How does the turnover rate differ between protein types?
- Regulatory or signalling proteins turnover quickly
- Structural or contractile proteins turnover slowly
51
What's the suggested protein requirements for non-athletes, endurance and strength athletes and patients with cancer?
Non-athlete = 0.8 g/kg/day
Endurance = 1.6 g/kg/day
Strength = 1.6 g/kgday
Cancer patients = 1-1.5 g/kg/day
52
What is required to gain muscle mass?
A positive protein balance where muscle protein synthesis exceeds muscle protein breakdown
53
How can positive protein balance be achieved?
By increasing protein synthesis OR decreasing protein breakdown OR combination of the 2
54
Does consuming more protein alone lead to muscle gain?
No resistance exercise is necessary alongside high protein intake
55
How does resistance exercise affect protein turnover?
It stimulates both muscle protein synthesis and muscle protein breakdown
56
How long does muscle protein synthesis stay elevated after resistance exercise?
Peaks around 3 hours and remains elevated for up to 48 hours or around 24 hours in trained individuals
57
Why is muscle protein breakdown important after exercise?
- It increases the availability of amino acids = more opportunity for protein synthesis
- Helps tailor muscle adaptations to the specific exercise performed (respond in a phenotypic way)
58
What happens to net protein balance (NPB) after resistance exercise? Explain it
It becomes less negative but still remains negative
- so just doing resistance exercise will not provoke muscle gain, just decreases the loss
59
SO what can turn net protein balance positive following resistance exercise?
Nutrition - specifically the intake of protein post exercise
60
Using stable isotope amino acid infusion combined with blood and muscle sampling following controlled resistance exercise and protein feeding
- resistance exercise often unilateral + lower body
- Manipulating different types of protein, amounts etc
61
Why is protein balance still important for endurance athletes?
Because they still require synthesis of specific proteins such as mitochondrial proteins not just muscle growth
62
What happens to amino acid oxidation during endurance exercise?
It increases especially the oxidation of BCAAs like leucine
= increased need for uptake
63
How does carbohydrate availability affect amino acid oxidation?
Lower carbohydrate availability increases amino acid oxidation
64
What percentage of energy is typically contributed by amino acids during exercise?
<5% but can be higher in low carbohydrate or low glycogen conditions
65
Why do endurance athletes still have an increased protein requirement?
Due to the need for mitochondrial protein synthesis (mitochondrial biogenesis) for endurance adaptations
66
In endurance exercise, when does protein intake enhance muscle protein synthesis?
Mostly during the post exercise recovery period
67
How does endurance exercise affect net protein balance?
It increases protein breakdown and synthesis especially when protein is ingested
- breakdown seen for both CHO and CHO+P group
- greater synthesis during and after exercise in CHO+P group
68
Which muscle proteins are most relevant to endurance vs strength exercise?
Mitochondrial proteins for endurance and myofibrillar proteins for strength
69
What did the exercise protein study find about protein synthesis in different fractions (myofibrillar vs mitochondrial separated out?
Protein ingestion increased myofibrillar protein synthesis but not mitochondrial synthesis acutely
70
Why might mitochondrial proteins not increase acutely after protein intake and exercise?
Because they may respond more slowly to exercise and nutritional stimuli
71
How did the 2 fractions of protein (myofibrillar vs mitochondrial proteins) respond to endurance and resistance exercise BEFORE a 10 week training programme?
- Resistance exercise stimulate myofibrillar synthesis but endurance did not
- Both endurance and resistance exercise stimulated mitochondrial protein synthesis
72
SO what does this mean at this point?
Muscle is not able to tell what the signal is at this point
73
What happened to MPS after a 10 week programme in either resistance or endurance specific training?
Muscle now learnt which fraction of protein to make based on exercise
- endurance = mitochondrial
- resistance = myofibrillar
74
How does resistance training affect protein synthesis at rest after 10 weeks training?
It sig. amplified resting protein synthesis and turnover in resistance trained muscle
75
How does muscle adapt to stop producing unneeded proteins after training?
It learns to stop synthesising proteins not beneficial for that type of exercise like mitochondrial proteins in resistance training
76
What is meant by protein balance throughout the day?
Periods of protein synthesis (stimulated when we eat) offset by periods of breakdown resulting in overall balance
- cancel each other out
77
How does exercise affect daily protein balance?
It amplifies muscle protein synthesis for several meals and reduces protein breakdown slightly leading to muscle gain over time
78
Can eating more protein alone lead to muscle gain?
No it must be combined with exercise to stimulate net protein gain
79
What proportion of ingested protein is actually used for muscle protein synthesis + where does the rest go?
About 2.2 percent
- 50% extracted by gut
- 10% made into other things
80
How much whey protein was found to maximise MPS in a single leg extension study?
20 grams
81
What happens to excess protein beyond what is needed for MPS?
It is oxidised and leads to increased urea production
82
Why might the single leg study underestimate actual protein needs for athletes?
Because most sports use whole body movements and have higher active muscle mass
- may also be dependent on body size
83
What did Macnaughton et al 2016 find about 20g vs 40g of whey protein after whole body resistance exercise?
40g led to significantly greater protein synthesis than 20g regardless of body size
- so nature of exercise appears to change the response
84
What may explain why 40g of protein was more effective after whole body exercise?
Greater total muscle mass was activated so more protein was needed for synthesis
85
For how long is muscle more sensitive to amino acids after resistance exercise?
At least 24 hours
86
What is the role of leucine and what has been proposed?
A leucine threshold has been proposed
- leucine is known to stimulate certain pathways that produce protein synthesis
- acute supplementation of leucine can increase protein synthesis response
87
What is the leucine threshold theory?
There is a specific level of blood leucine that must be reached to trigger muscle protein synthesis
88
Why is the type of protein source important for MPS?
Because different sources produce different effects on blood leucine
- some are giving increased responses
89
What role does leucine play in protein synthesis?
It activates the mTOR pathway which stimulates muscle protein synthesis
90
What chronic effects has protein supplementation been shown to have?
Increases in...
- 1RM strength
- Fat free mass
- Muscle size
