Biochem Flashcards
Glycogen is a combination of 2 things:
Glycogenin (core protein)
Multiple glucose molecules (bonded together in chains)
In glycogen, glucose molecules are joined together by ———–
glycosidic bonds
Glycosidic bonds can be:
——- forming straight chains OR ——– which allows branching
α 1-4 forming straight chains OR α 1-6 which allows branching
What are the purpose of branches in glycogen?
To allow multiple points of breakdown as glycogen can only be broken down from the ends.
2 forms of glycogen
Liver glycogen (storage system to maintain blood glucose between meals) Muscles glycogen (source of energy to muscle tissue during exercise)
Glycogenesis has an activated intermediate called ———–
UDP-glucose
best thought of an activated form of glucose in the same way ATP is activated phosphate
Glycogenesis rate limiting enzyme
hexokinase
glucose»_space; glucose-6-phosphate
Glycogenesis enzymes
Hexokinase = rate-limiting enzyme (glucose»_space; glucose-6-phosphate)
Glycogen synthase = α 1-4 (UDP-glucose»_space; glycogen)
Transglycosylase = α 1-6 (UDP-glucose»_space; glycogen)
Gluconeogenesis
Production of glucose from a non glycogen source
e.g. amino acids, lactate and glycerol
Gluconeogenesis is powered by ———–
oxidation of lipids
The cori cycle
the process that recycles lactate formed by anaerobic respiration (lactate»_space; pyruvate»_space; glucose).
A TYPE OF GLUCONEOGENESIS
The cori cycle occurs in the ———-
liver
Lactate formation requires —– ATP
Cori cycle requires —– ATP
Lactate formation requires 2 ATP
Cori cycle requires 6 ATP - very energy insufficient
glycogenolysis - reaction steps
Glycogen + Pi»_space;> smaller glycogen + glucose-1-phosphate (this is immediately converted to glucose-6-phosphate)
In the liver, glucose-6-phosphate»_space; glucose
In muscle, glucose-6-phosphate provides energy via glycolysis.
Glycogenolysis rate limiting enzyme
glycogen phosphorylase
|»_space; glucose-1-phosphate
Lipids vs Triglycerides
Long chains mostly hydrocarbons vs 3 fatty acids + glycerol backbone
Triglyceride function
Compact energy source (major storage form in adipose tissue)
Lipids - 3 forms
Simple: fatty acids, waxes and triglycerols
Compound: phospholipid, glycolipids, lipoproteins
Steroids: cholesterol, hormones
How do fats enter the mitochondria?
Lipids are converted to a usable form - Acetyl CoA.
Needs a carrier molecule to be transported = Acyl carnitine/Acyl CoA.
Transported via CARNITINE SHUTTLE
Describe the carnitine shuttle
Carnitine + Acyl CoA»_space;> Acyl carnitine
(Acyl carnitine is exchanged into cell through a translocase molecule - acyl carnitine transporter)
Acyl carnitine»_space;> Carnitine + Acyl CoA
This replenishes Carnitine for the exchange with Acyl carnitine
Breakdown of triglycerides (2 steps)
1) Forming Acyl-CoA = cytoplasm, needs CoA, 2ATP (fatty acid + CoA»_space; Acyl CoA)
2) Β-oxidation = mitochondrial matrix, needs NAD, FAD2 + H2O - doesn’t need energy
How many cycles of B-oxidation for C19?
8 cycles
19/2 = 9.5, round to 9, 9 - 1=8
(divided by 2, minus 1)
Products of B-oxidation?
1 Acetyl CoA 1 FADH2 1 NADH + H+ 1 fatty AcylCoA - 2 carbons (at the end, 1 extra AcetylCoA or propionyl-CoA)
Energy level of β-oxidation
Each acetyl-CoA makes 1 FADH2 , 3 NADH and 1GTP
FADH2 = 1.5ATP
NADH = 2.5ATP
GTP = 1 ATP
Ketones are produced in ————
Used in ———-
Ketones are produced in the mitochondria of the liver
Diffuse out to the peripheries) and used in the heart and kidneys (converted back to Acetyl CoA
Ketones can cause problems in ———
Starvation or diabetes
Oxaloacetate is used up for gluconeogenesis so ketones can’t be broken down.
Ketone levels rise, leading to acidosis (ketones = weak acids)
Lipogenesis
de novo synthesis of fatty acids
Lipogenesis location
mostly in the liver, kidneys, mammary glands, adipose tissue and the brain
Lipogenesis occurs when ———
excess energy is consumed (mostly excess carbs)
Lipogenesis is controlled by ——
Insulin - promotes storage
Glucagon - signals breakdown
Citrate - allosteric (lots of citrate promotes movement out of the mitochondria)
Fatty acid synthesis =
In ———– cells starch is broken down»_space; ————-
This is transported by ———- into the cytoplasm.
Then ———– is formed (a precursor for synthesis)
In hepatocytes, starch is broken down»_space; acetyl CoA
This is transported by citrate into the cytoplasm.
Then Malonyl-CoA is formed (a precursor for synthesis)
4 reactions of fatty acid synthesis
Condensation
Reduction
Dehydration
Reduction and release
Malonyl-CoA is a ———-
It is formed from ———– by ————
Carbon doner formed from acetyl CoA by acetyl-CoA carboxylase
In lipogenesis, a special acyl-carrier protein is used called ———–
ACP
Fatty acids are synthesised by a cycle of reaction =
1) a starter chain is attached to ACP
2) acetyl-CoA + malonyl-CoA are used to add 2 C atoms per cycle; this consumes NADPH (e- donor)
* **extra enzymes exist to elongate the chain further or add unsaturated bonds
Synthesis of triglycerides
Glycerol-3-phosphate (G-3-P) + 3 fatty acids form a triglyceride through esterification.
G-3-P is formed from ————
1) glycerol in the liver
2) glucose in the adipose tissue
Glycerol-3-phosphate
ACTIVATED glycerol
What other products similar to triglycerides are also produced in the liver?
phospholipids, cholesterol and lipoproteins
Break down of amino acids produces —– and ——— which are both are toxic
NH3 and NH4+
MUST BE EXCRETED AS BUILDUP IS DANGEROUS
Amino acid absorption
1) Proteolytic enzymes in stomach/intestine produce single amino acids
2) Absorbed into intestinal cells
3) Released into blood
Amino acid transamination
Moving the amino group from an amino acid to an alpha keto acid (happens in all tissues)
Amino acid deamination
Conversion of amino groups to free ammonium ions
Synthesis of urea location
mitochondrial matrix of hepatocytes
Synthesis of urea purpose
a way of making the toxic NH4+ through less toxic products to urea that can be excreted
Deamination of amino acids results in leftover ——–
carbon skeletons
The carbon skeletons leftover from amino acid deamination have 2 fates:
1) conversion to glucose - glucogenic (degraded to pyruvate, which can go to glucose)
2) to be oxidised in the TCA cycle - ketogenic (degraded to acetyl-CoA and can form ketone bodies)
The dangerous components of amino acids are excreted as which molecules?
Urea (80%, in the liver), uric acid, creatinine, NH4+
The products of amino acid transamination are transported to the liver via two transport molecules =
alanine and glutamine
