40 Questions
What happens to the blood sugar level when it is decreased to approximately half?
It leads to coma due to lack of glucose in brain cells.
Where is most of the hypoglycin found in ackee fruit?
In the seed
What role do amino acids play in higher animals?
They serve as building blocks for proteins and precursors for various biomolecules.
What major fates do amino acids' carbon skeletons have when they are used as fuel?
Oxidation to CO2 via TCA
How do vertebrates digest proteins for absorption?
Proteins are digested into amino acids or di- or tripeptides before absorption.
What is the term used to refer to each unit of an amino acid sequence?
Residue
How do amino acids serve as a source of energy when ingested in excess?
They undergo gluconeogenesis to form glucose.
What happens when brain cells lack glucose?
Coma may occur
What happens to a protein if the disulfide bridge linking the A-chain and B-chain of insulin is broken?
It becomes inactive
Which amino acid is responsible for the formation of disulfide bonds in proteins?
Cysteine
What is the structural difference between cysteine and cystine?
Presence of an extra CH2 group
Which amino acid is known for its polarity due to the amide group?
Asparagine
Which amino acid functions as a hydrogen bond donor?
Glutamine
Which amino acid is negatively charged and referred to as aspartate when charged?
Aspartic Acid
How many hydrophilic residues typically occur on the exterior surface of proteins?
Four
What is the function of the CO group in proteins?
H-bond acceptor
What physiological symptoms do phenylketonurics experience?
Severe mental symptoms
How does phenylketonuria affect tyrosine metabolism?
Inhibits tyrosine hydroxylation
What skin-related condition is commonly observed in phenylketonurics?
Albinism
Why do phenylketonurics have lighter skin and hair colour compared to their siblings?
Impaired melanin synthesis
What is the first step in the formation of melanin?
Tyrosine hydroxylation by tyrosinase
What are the common CNS symptoms associated with phenylketonuria?
Hyperactivity and seizures
What is the recommended therapy for phenylketonuria patients?
Low phenylalanine diet
Why is early diagnosis crucial for phenylketonuria?
Prevent irreversible brain damage
What is the major biochemical abnormality associated with Parkinson's Disease?
Degeneration of cells in the substania nigra and locus coelureus
Which neurotransmitter is primarily affected in Parkinson's Disease?
Dopamine
What happens to the release of dopamine as the number of surviving cells decreases in Parkinson's Disease?
It decreases
Why is the administration of DOPA used in Parkinson's Disease treatment?
To relieve tremor symptoms temporarily
What fate do ketogenic amino acids meet during degradation?
Converted into ketone bodies
What distinguishes glucogenic amino acids from ketogenic amino acids in terms of degradation?
They can be converted to glucose
What is the common fate of the carbon atoms from the degradation of amino acids?
Funneled into seven major metabolic intermediates
What happens to dopamine levels when its concentration exceeds a certain threshold in Parkinson's Disease?
Dopamine becomes toxic
What is the purpose of transamination?
To form glutamate by collecting amino groups
Which enzyme is responsible for the formation of ammonia from glutamate?
Glutamate dehydrogenase
What is the prosthetic group of all transaminases?
Pyridoxal phosphate
Where does oxidative deamination take place in the cell?
Mitochondria
What are the products of the reaction Glutamate + Oxaloacetate?
NH3 + alpha-ketoglutarate
Why is it essential to convert NH4+ to urea in the liver?
To prevent NH4+ buildup in tissues
Which amino acid reacts with alpha-ketoglutarate to form p-phenylpyruvate and glutamate?
Tyrosine
What is the nitrogen acceptor in the transamination reaction?
Alpha-ketoglutarate
Study Notes
Amino Acid Metabolism
- Amino acids serve as building blocks of proteins and as precursors of many other important biomolecules such as hormones, purines, pyrimidines, porphyrins, and vitamins.
- They also serve as a source of energy, particularly when they are ingested in excess.
Digestion
- Proteins cannot enter epithelial cells, and must be digested into amino acids or di-or tripeptides before absorption can occur.
- Digestion involves several stages, including extraction of proteins from food, denaturation of proteins, and more.
Transamination
- Glutamate plays a crucial role in collecting amino groups from all over to form glutamate.
- Transamination reactions involve the transfer of an amino group from an amino acid to a keto acid, resulting in a new amino acid and a keto acid.
- Examples of transamination reactions include:
- Glutamate + Oxaloacetate → α-KG + Aspartate
- Ala + KG → Pyruvate + Glutamate
- Asp + KG → OAA + Glutamate
- Leu + KG → Ketoisocaproate + Glutamate
- Tyrosine + KG → p-phenylpyruvate + Glutamate
Oxidative Deamination
- Glutamate is converted to α-KG and ammonia through oxidative deamination, catalyzed by glutamate dehydrogenase.
- The enzyme responsible is GLUTAMATE DEHYDROGENASE, a mitochondrial enzyme.
- The reaction involves the transfer of a hydride ion, with NAD+/NADP+ serving as a co-factor.
Phenylketonuria (PKU)
- PKU is a genetic disorder characterized by the inability to metabolize phenylalanine.
- Symptoms include mental retardation, seizures, hyperactivity, and tremors.
- The condition is diagnosed by testing urine with FeCl3, which gives a green olive color in the presence of phenylpyruvate.
- Treatment involves a low-phenylalanine diet, which must be started at birth to avoid irreversible brain damage.
Parkinson's Disease
- Parkinson's disease is a neurodegenerative disorder characterized by the degeneration of cells in certain areas of the brain, leading to a deficiency of dopamine.
- Symptoms include tremors, which can be relieved by administering DOPA.
- The administration of DOPA is not a permanent cure, and the disease remains uncontrolled.
Fates of Carbon Atoms of Degraded Amino Acids
- The carbon skeletons of 20 amino acids are funneled into seven major metabolic intermediates, including pyruvate, acetyl-CoA, acetoacetyl-CoA, α-KG, succinyl-CoA, fumarate, and OAA.
- Amino acids can be classified into ketogenic or glucogenic based on their fate.
- Ketogenic amino acids are degraded into acetyl-CoA or acetoacetyl-CoA, while glucogenic amino acids are degraded into pyruvate, α-KG, succinyl-CoA, fumarate, or OAA.
Test your knowledge on transamination reactions with this quiz. Learn about the conversion of amino acids to different compounds like ketoglutarate and glutamate. Explore how transamination helps in the synthesis of various important molecules.
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