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Protein Flashcards

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1
Q

What is Protein?

A
  • 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
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2
Q

Essential (indispensible) aa

A

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

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3
Q

Amino Acids can be grouped on the basis of:

A
  • 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
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4
Q

conditionally essential (indispensible) aa

A

usually not essential, except in times of illness and stress
1. Arginine
2. Cysteine
3. Glutamine
4. Proline
5. Tyrosine

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5
Q

Non-essential (dispensible) aa

A
  1. Alanine
  2. Aspartic acid*
  3. Asparagine
  4. Glutamic
    Acid†
  5. Glycine
  6. Serine
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6
Q

Protein Digestion occurs where?

A

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

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7
Q

Protein Absorption
- where?
- uses?
- dependent on?
- absorbed through?
- also needs a ______ system

A
  • 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
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8
Q

Protein Absorption
- capacity
- peptides have their own _______
- which aa are absorbed more easily?
- supplements with high amounts of one aa may?

A
  • 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
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9
Q

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 ________-

A
  • 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
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10
Q

Hormones with a role in protein synthesis

A
  • 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
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11
Q

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

A

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

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12
Q

Structural role of protein

A
  • 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
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13
Q

buffering role of protein

A
  • 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
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14
Q

fluid balance role of protein

A
  • Attract and keep water in a particular location by contributing to osmotic pressure
  • Imbalance contributes to oedema or ascites
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15
Q

catalyst role of protein

A
  • Enzymes
  • Bind with substrate to generate a product
  • Often require a cofactor or coenzyme
  • Multiple physiological processes depend
    on enzymes
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16
Q

messenger role of protein

A
  • Hormones – chemical messengers in the body
  • Synthesized and secreted by endocrine organs
  • Transported in blood to other locations where
    they bind with protein receptors
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17
Q

immunoprotection role of protein

A
  • 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
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18
Q

transport role of protein

A
  • 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
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19
Q

acute phase responder role of protein

A
  • 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
20
Q

N-Containing Nonprotein Compounds

A
  • 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
21
Q

Protein turnover

A

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

22
Q

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

A
  • protein nutritional and anabolic
    vs catabolic
  • N and excretion
  • protein N and nucleic acids, creatine from meat, vitamins
  • relative
23
Q

Factors affecting N balance:
Positive balance

A

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

24
Q

Factors affecting N balance:
Negative balance

A

Physiological state
* injury, surgery
* burns
* bleeding
* proteinuria
* diarrhoea
Nutritional state:
* not enough E
* not enough P
* switch from high to low P diet

25
Q

To synthesize an AA requires ability to make its _________ _______ from endogenous sources
* E.g. Pyruvate, α-ketoglutarate & oxaloacetate (all derived from the citric acid cycle)

A

carbon skeleton

26
Q
  • Transamination is the transfer of amino group from one AA to an _____ ______ ____
  • Forms _________ AAs as required eg to match dietary AA with body needs for protein synthesis
  • Requires vitamin __ as coenzyme
  • AAs able to be formed in this way are _______, _______ acid and _______ acid
  • Most transamination reactions are catalysed by ___________
  • Reversible
A

alpha keto acid
different
B6
alanine, glutamic acid and aspartic acid
aminotransferases

27
Q

Protein Degradation

A

i. Deamination to ammonia:
* removal of amino gp (mainly from glutamate)
* to form alpha-keto acid ‘C skeleton’ with release of NH4+
ii. Oxidation to energy
* C skeleton can enter TCA cycle
So, the C skeleton of AAs can be:
→ glucose (overnight fast)
→ ketones (long term fasting, or diabetes)
→ fat biosynthesis? (xs P intake)

28
Q

Protein Detoxification

A

NH3 is the toxic end product of P metabolism
* transported to liver for urea synthesis via incorporation
into glutamine (most tissues) or alanine (muscle)
* safely excreted via kidneys (2/3rds) or GIT (1/3rd):
N excretion as urea varies according to P requirement:
* urea can be reabsorbed from kidney tubules, or
* degraded by bacteria in colon to reform -NH2 which
can be reabsorbed back to liver i.e. urea N is salvaged

29
Q

Factors that increase protein requirements

A

Increased breakdown of muscle (stress response)
* injury, surgery, burns
* cancer cachexia
Increased losses of protein
* bleeding, diarrhoea
Increased retention of protein
* growth, pregnancy
* muscle building plus exercise

30
Q

How do we maintain N balance
with low P intake?

A
  1. ↓ N retained in labile P pool
  2. ↓ P turnover in tissues i.e. synthesis + degradation.
  3. ↓ P oxidation:
    * C skeleton → ATP, glucose
    * NH2 group → urea synthesis
    urea excretion
  4. ↑ salvage of urea N
31
Q

How do we maintain N balance
with high P intake

A
  1. ↑ N retained in labile P pool
  2. ↑ P turnover in tissues i.e. synthesis + degradation
  3. ↑ P oxidation:
    * C skeleton → ATP, glucose
    * removal of NH2 gp
    → urea synthesis & excretion
  4. Conversion to fat?
  5. ↓ Salvage of urea N
32
Q

Is a high protein diet harmful?

A
  1. increase urea excretion:
    * obligatory H2O loss may → dehydration
    * risk groups
    * infants
    * elderly
    * athletes
  2. increase Ca excretion
    * ? may contribute to osteoporosis
  3. ‘Rabbit’ starvation’
    * inadequate fat & carbohydrate. in early pioneers
33
Q

Consequences of Inadequate Protein 1

A

Marasmus – a severe
deficiency of energy
* Frail, emaciated appearance,
impaired growth, weakness,
apathy, thin, dry hair, low body
temperature & BP, prone to
dehydration & infections

34
Q

Consequences of Inadequate Protein 2

A
  • Kwashiorkor
  • Historically considered a severe deficiency
    of protein. This has been challenged.
  • Oedema in the legs, feet, and stomach,
    diminished muscle tone and strength,
    rashes, lesions, brittle hair, prone to
    infection, sadness, apathy, excess fluid in
    the lungs, septicaemia, pneumonia, water &
    electrolyte imbalance, death
35
Q

Consequences of Inadequate Protein 3

A

Protein-energy malnutrition (PEM) – a lack of sufficient dietary protein &/or
energy
* In Australia most malnutrition is disease related
Multiple health problems including
GI tract breakdown
Impaired immune function
Muscle loss & reduced strength
Fluid imbalance
Reduced mental function and QOL

36
Q

Assessment of Protein Status -
Anthropometry

A
  • Mid-upper arm muscle area
  • Estimate of changes in skeletal muscle
  • In vivo neutron activation analysis (research)
  • Allows direct estimation of the amount of N in the body
  • Bioelectrical impedance analysis, Computerized tomography,
    magnetic resonance imaging or dual energy X-ray
    absorptiometry
  • Estimate skeletal muscle mass
37
Q

Assessment of Protein Status –
Biochemistry – Serum Proteins

A

Total serum protein
* Insensitive as a nutrition marker. Only depleted when clinical signs of malnutrition apparent. Influenced by
many factors besides nutrition
Serum albumin
* Half-life of 14-20d so not sensitive to short-term changes. Influenced by many other factors e.g.
inflammation, disease Not a useful indicator of protein status or malnutrition in most circumstances
Serum transferrin
* Transports iron. Half-life 8-19d so responds more rapidly to change. Influenced by many factors e.g.
Inflammation, disease, Fe status. Not a useful indicator of protein status or malnutrition in most
circumstances
Serum retinol-binding protein (RBP)
* Carrier for retinol. Half life 12 hours so changes rapidly in response to dietary intake. However influenced
by multiple other factors e.g. Liver disease, catabolic states, vitamin A status. Not a useful indicator of
protein status or malnutrition in most circumstances
Serum transthyretin (also called prealbumin or thyroxin binding prealbumin)
* Transports thyroxine, carrier for RBP. Half life 2d. More sensitive indicator of protein energy malnutrition
than albumin. Responds rapidly to short-term effects of nutrition therapy. Influenced by many diseases,
although not as quickly as other serum proteins. Not used in most malnutrition screening/assessment tools.
Useful as part of assessment in some circumstances alongside other data e.g. Clinical and dietary.

38
Q

Assessment of Protein Status –
Biochemistry (selected other)

A
  • Urinary creatinine excretion
  • Derived from breakdown of creatine phosphate in muscle.
    If creatine in muscle is constant urinary creatine indicates
    muscle mass
  • Requires at least 3d plus low creatine diet. Not practical
    in the clinical setting
  • Nitrogen Balance
39
Q

Assessment of Protein Status – Functional
Tests – Selected

A
  • Handgrip strength
  • Uses a handgrip dynanometer
  • Subjects perform a maximal contraction for a few seconds
  • Results compared to interpretative criteria
  • Have been found to be signficant predictors of
    malnutrition/malnutrition related complications
  • Immunological tests
  • Changes have been observed in protein-energy malnutrition
  • Influenced by many other factors besides nutrition
  • Markers include lymphocyte count, thymus-dependent
    lymphocytes, delayed cutaneous hyper-sensitivity, cytokines
40
Q

Assessment of protein status – malnutrition
assessment tools

A
  • Tools available for screening and assessment
  • Multiple tools available worldwide.
  • Malnutrition Screening Tool, Subjective Global Assessment (SGA)
    and Patient Generated SGA (PG-SGA) are commonly used tools
    in Australia
  • Assess multiple types of data including weight change, dietary
    intake, nutrition impact symptoms, functional status, disease and
    physical assessment of muscle and fat mass and wasting
41
Q

Assessment of Protein Status – Other
methods

A
  • Dietary intake – usual limitations apply
  • Clinical – used in the interpretation of other data
42
Q

high protein foods (10-30g)

A

gelatine (84g)
meat, fish, cheese, egg
wheat germ, yeast
soybean, nuts

43
Q

moderate protein foods (3-10g)

A

breakfast cereals, milk
bread, lentils & beans
rice, pasta

44
Q

low protein foods (less than 3g)

A

beverages, fats & oils
potatoes & other veg’s
fruit, juices

45
Q
A

Nutrition Science (14 decks)

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