Biochemistry Flashcards
What is glycogenesis?
Synthesis of glycogen from glucose
What is glycogenolysis?
Breakdown of glycogen to form glucose
Glycogenolysis occurs by hydrolysis.
True/ False?
False
Occurs by phosphorolysis
Where is glycogen stored in the body?
Liver
Muscle cells
What is the role of muscle glycogen?
Not used to maintain blood glucose; provides energy via glycolysis and TCA cycle during physical activity
Which bonds link glucose molecules to form glycogen?
Alpha-1,4-glycosidic bonds
Which bonds create branches in the glycogen chain?
Alpha-1,6-glycosidic bonds
Glycogen formation can be started by two glucose monomers joining together.
True/ False?
False
Glucose residues can only be added to an existing glycogen chain
What is required to begin glycogen formation?
Glycogenin
What is glycogenin?
A glycogen primer containing 4 glucose monomers
Which enzyme effectively adds glucose monomers to glycogenin to produce glycogen?
Glycogen synthase
When enough glucose is present, glycogen synthesis begins: glucose-6-phosphate is converted to what?
Glucose-1-phosphate
What is formed from glucose-1-phosphate in glycogen synthesis?
UDP-glucose
What is UDP-glucose?
Essentially an active form of glucose
Glycogen synthase adds only one glucose at a time to UDP-glucose to ultimately form glycogen.
True/ False?
True
How often are branches introduced into the glycogen chain?
Every 10 glucose molecules
When does glycogenolysis occur?
Between meals to maintain blood glucose levels
Which enzyme catalyses glycogenolysis?
Glycogen phosphorylase
Glycogen phosphorylase cleaves off only one glucose at a time from glycogen.
True/ False?
True
What are the 2 regulatory actions of insulin upon glycogen synthesis?
Stimulates glycogen synthesis
Inhibits glycogen phosphorylase
What are the 2 regulatory actions of glucagon upon glycogenolysis?
Stimulates glycogen breakdown
Inhibits glycogen synthase
What is gluconeogenesis? When does it occur?
Synthesis of glucose from non-carbohydrate precursors
Occurs when glycogen stores are completely depleted
Where does gluconeogenesis mainly occur?
Liver
Name the 3 main precursors for gluconeogenesis!
Lactate (lactic acid)
Amino acids
Glycerol
Which TCA cycle intermediate is needed for gluconeogenesis? Why is it needed?
Oxaloacetate (4C)
Accepts acetyl groups from fat breakdown
Describe the Cori Cycle!
Blood transports lactate to liver
Liver converts lactate to glucose
Glucose is released into blood
Which type of amino acids can be used to synthesise new glucose?
Glucogenic amino acids
Which type of amino acids cannot be used to synthesise new glucose?
Ketogenic amino acids
What effect do insulin and glucagon have on gluconeogenesis?
Insulin inhibits gluconeogenesis
Glucagon stimulates gluconeogenesis
Does ATP stimulate gluconeogenesis?
Yes
What happens when increased fat intake is not coupled with appropriate energy expenditure?
Obesity
Increase in number and size of adipocytes
Fat provides us with 2x more energy than carbohydrates.
True/ False?
True
What are essential fatty acids?
Fatty acids required that cannot be synthesised by the body
Name some fat-soluble vitamins!
Vitamin A, D, E, K
What do triglycerides consist of?
Glycerol attached via ester bond to 3 fatty acids
Double bonds in fatty acids are usually in the trans configuration.
True/ False?
False
Usually in cis configuration
What effect do double bonds have on the melting point of fatty acids?
The greater the no. of double bonds, the lower the melting point
What are the main products of lipid digestion?
Glycerol
Fatty acids
Monoglycerides
What must happen to long-chain fatty acids to make them transportable?
Resynthesised to triglyceride and coated into a chylomicron, which enters the lymph
What happens to chylomicrons at muscle and adipose tissue?
Cleaved by lipoprotein lipase into free fatty acids
What happens to free fatty acids at muscle and adipose tissue?
Resynthesised into triglyceride or oxidised to provide energy
Where does further oxidation of fatty acid occur?
Why is this a problem for acyl-CoA?
Oxidation occurs in the mitochondrial matrix
Acyl-CoA is formed in the cytoplasm!
What transports acyl-CoA into the mitochondrial matrix?
Carnitine shuttle
How is acyl-carnitine formed in the cytoplasm?
Fatty acids are transferred from acyl-CoA to carnitine to form acyl-carnitine
How does acyl-carnitine get across the inner membrane into the matrix
What happens to the carnitine?
Via a transporter
Carnitine is cleaved off, leaving acyl group
In the matrix, what happens to the free acyl- group?
Combines with CoA again to form acyl-CoA
Net effect: acyl-CoA ends up in the matrix!
What happens to acyl-CoA in the matrix?
Shortened by 2C to form acetyl-CoA and a new acyl-CoA
What are the products of one round of B-oxidation of fatty acid?
1 acetyl-CoA
1 acyl-CoA, shortened by 2C
1 FADH2
1 NADH + H
How and where are ketone bodies formed?
Formed from acetyl-CoA during B-oxidation in liver mitochondria
What is lipogenesis?
Synthesis of fatty acids
Lipogenesis is a reductive process (electrons are required).
True/ False?
True
What transports acetyl-CoA from mitochondrial matrix into cytoplasm?
Citrate
What is the vital first step in lipogenesis from acetyl-CoA?
Activation of acetyl-CoA by acetyl-CoA carboxylase into malonyl-CoA
Which enzyme catalyses synthesis of long chain fatty acid from malonyl-CoA, acetyl-CoA and NADH?
Fatty acid synthase
Which component of fatty acid synthase carries the growing fatty acid chain during synthesis?
Acyl-carrier protein (ACP)
Lipogenesis:
When a fatty acid chain length of __C is reached, the fatty acid is released.
16C
Synthesis of fatty acids is maximal when carbohydrate is scarce.
True/ False?
False
Synthesis occurs when carbohydrate is in plentiful supply + fatty acids are scarce (otherwise lipolysis would occur)
Amino acids which are not used for proteins are stored in the liver.
True/ False?
False
Amino acids cannot be stored and are degraded if not used as building blocks
Where is the major site of amino acid degradation?
Liver
What does amino acid degradation primarily produce?
Ammonia and ammonium ions that form urea
What are the 3 steps by which urea is formed?
Transaminiation
De-amination
Urea cycle
Which organ is albumin secreted from?
Liver
Name the main liver-derived plasma proteins (4), in order of increasing molecular weight!
Albumin - transport
Alpha-globulins - transport
Beta-globulins - transport
Gamma-globulins - antibodies
What characteristic of plasma proteins enables them to maintain osmotic pressure which increases fluid movement out of the tissues into the blood?
They are insoluble - they do not diffuse into the interstitial fluid and only circulate in the blood
List some hydrophobic substances that are carried in the blood by plasma proteins (4)!
Steroid hormones
Free fatty acids
Bilirubin
Cholesterol
Give 2 examples of alpha-globulin plasma proteins!
Ceruloplasmin - stores and carries copper
Retinol-binding protein
Give 2 examples of beta-globulin plasma proteins!
Transferrin - transports iron
Fibrinogen
Transferrin transports Fe2+ (ferrous iron).
True/ False?
False
Transports Fe3+ (ferric iron)
What is the most abundant plasma protein in the blood?
Albumin
Insulin inhibits production of albumin.
True/ False?
False
Insulin stimulates production of albumin
Are albumin levels low or high in liver disease?
Low
Iron is transported in the ferrous/ferric state bound to ____, and is stored in the ferrous/ferric state bound to ____
Iron is transported in the ferric state bound to transferrin, and is stored in the ferrous state bound to ferritin
Which plasma protein does copper bind to for transport?
Ceruloplasmin
Which disease results due to accumulation of copper due to deficiency of ceruloplasmin?
Wilson’s disease
