Protein Metabolism and Nitrogen Balance

Question 1

How are proteins absorbed

Answer 1

• absorbed in ileum as amino acids via secondary active transport
• digestion is slow ( hours )

Question 2

Describe protein concentration in tissues and what happens to excess

Answer 2

• high turnover between tissues = rapid distribution

- will be expelled in urine if there is too much and proximal tube can’t reabsorb

Question 3

Describe the metabolism of proteins

Answer 3

• broken into amino acids which are used for energy
• Amino acids undergo deamination which breaks it into glucose, fatty acids and ketone and Ammonia
• ammonia is expelled in urea

Question 4

How are amino acids stored? what happens when protein is needed?

Answer 4

• free amino acids can’t be stored so they combine to form peptides and intracellular proteins
• when protein is needed intracellular proteins are degraded into amino acids and the transported in blood

Question 5

Where are proteins stored

Answer 5

• liver stores most proteins along with kidneys and intestinal mucosa
• can’t be stored by cells unless AA convert to fat/glycogen

Question 6

What influences the storage of amino acids

Answer 6

• hormone and insulin increases protein synthesis

- glucocorticoid mobilize amino acids for energy

Question 7

What are the 4 plasma proteins and their function

Answer 7

• Albumin : generates osmotic pressure
• Globulins : innate and acquired immunity
• Transferrin : carry ferrous ions
• Fibrinogen: mediates clot formation and repairs leaks in Circulation

Question 8

What produces plasma protein and what can affect the rate of production

Answer 8

• plasma is formed by the liver
• in stress conditions production increases
• in liver disease it decreases and thus causes oedema

Question 9

List the 4 stages of protein metabolism in liver

Answer 9

1- Transamination
2- Deamination
3- Oxidation
4- Excretion

Question 10

Describe Transamination & the main substrate used

Answer 10

• amino group transferred from amino acid to alpha keto acid by aminotransferase
• glutamine amino is usually used

Question 11

What is the effect of aminotransferase on protein synthesis

Answer 11

aminotransferase used vitamin B6 which decreases protein synthesis

Question 12

Describe Deamination

Answer 12

• amino group is removed from amino acids

- amino acid is converted to ammonia which is excreted in urea

Question 13

Describe role of alpha ketoglutarate

Answer 13

• amino acid and alpha ketoglutarate through aminotransferase will make glutamate and alpha keto acid.
• glutamate will make ammonia
• alpha ketoglutarate can also enter TCA cycle (gluconeogenesis )

Question 14

Explain Gluconeogenesis and amino acids

Answer 14

• alpha ketoglutarate will enter TCA cycle which contains amino acids
• amino acids can also generate pyruvate

Question 15

Explain Ketogenesis and amino acids

Answer 15

• amino acids can create Acetyl CoA

- synthesise ketones and lipids

Question 16

What are the 5 classes of amino acids

Answer 16

1- Essential 
2- Non-essential 
3- Glucogenic 
4- Ketogenic 
5- Glucogenic and Ketogenic

Question 17

How is Urea formed

Answer 17

• Ammonia released from deamination is ionized with carbon dioxide to create ammonium ( NH4)
• one amino from ammonium makes citrulline that combines with amino from aspartate to make arginine that with water becomes urea

Question 18

What does Urea contain

Answer 18

Ornithine 
Carbamoyl phosphate ( reactor )
Citrulline 
Aspartate ( reactor ) 
Arginiosuccinate 
fumarate 
arginine 
= urea

Question 19

What is the purpose of Urea

Answer 19

prevents toxic build up of ammonium

Question 20

how is Protein used as a source of energy and when

Answer 20

• used for gluconeogenesis

- only used if all carb and fat stores are used

Question 21

What happens with liver phosphorylase deficiency

Answer 21

• will not be able to mobilize glycogen from liver and thus gluconeogenesis and ketogenesis will be used for fuel

Question 22

Growth hormone effect protein metabolism

Answer 22

• promotes synthesis of cellular protein
• increase amino acid membrane transport
• increase RNA transcription

Question 23

Insulin effect on protein metabolism

Answer 23

• promotes cellular uptake of AA
• inhibits protein catabolism
• increase RNA transcription
• decrease gluconeogenesis

Question 24

What hormones are needed for protein synthesis

Answer 24

• growth hormone and insulin

- needed TOGETHER

Question 25

Testosterone and Oestrogen effect on protein metabolism

Answer 25

• T: transient muscle growth

- O: minor muscle growth relative to testosterone

Question 26

Thyroxine effect on protein metabolism

Answer 26

• increases cell metabolism which activates catabolic protein pathways
• will increase protein synthesis if high carbs and fats and degradation if low

Question 27

Glucocorticoids effect on protein metabolism

Answer 27

• increase protein break down and circulating AA and plasma proteins

Question 28

Explain Citrullinemia

Answer 28

deficiency in arginosuccinate synthase results in accumulation of ammonia in blood

Question 29

Explain Tyrosinemia

Answer 29

defective liver tyrosine aminotransferase will result in liver disease, osteoarthritis and mental retardation

Question 30

Explain Phenylketonouria

Answer 30

mutation in PAH gene result in lack of phenylalanine hydroxyls which damages CNS

Question 31

What is nitrogen balance and its purpose

Answer 31

• nitrogen is fundamental part of AA
• balance is determined by amount consumed and excreted
• nitrogen will indicate protein metabolism , if intake is greater than loss then no demand of stored protein breakdown

Question 32

Effects of negative nitrogen balance

Answer 32

• Cachexia : loss of body mass

- hyper metabolic state : constant protein break down which can lead to sepsis