L18: Post-Absorptive Metabolism Flashcards
*List the major metabolic fuels
- Glucose
- FFA
- Glycogen
- Ketone bodies
- Triacylglycerols
*
Can nutrients be converted from one form to another?
Yes. eg fat can be obtained from food, or synthesised from protein or CHO
What molecule is the main energy currency?
ATP
(adenosine triphosphate)
*Understand what is meant by ATP being the energy currency
What is the structure of ATP?
contains 3 phosphate bonds, two of which are high energy
*Understand the various fates of glucose
What is glucose converted to when it enters a cell?
What is the four possible fates of this molecule?
- Converted to glucose-6-phosphate by glucokinase or hexokinase
- 4 possible fates:
- *-Aerobic metabolism** to generate energy
- *-Anaerobic metabolism** to generate energy
- *-Glycogen synthesis** for short-term energy store
- *-Fat synthesis,** for long-term energy store
*Understand what is meant by ATP being the energy currency
What are the four stages of aerobic glucose metabolism, and how many ATP in total does it produce?
- stage 1: glycolysis (glucose => pyruvate)
- stage 2: pyruvate converted to acetyl CoA
- Stage 3: citric acid cycle
- stage 4: oxidative phosphorylation
- TOTAL ATP PRODUCED = 38
_*Understand what is meant by ATP being the energy currency_
How many ATP is produced in stage 1 of aerobic metabolism?
2 ATP and 4 H
_*Understand what is meant by ATP being the energy currency_
How many ATP is produced in stage 2 of aerobic metabolism?
No ATP and 4 H
*Understand what is meant by ATP being the energy currency
How many ATP is produced in stage 3 of aerobic metabolism?
16H and 2 ATP
_*Understand what is meant by ATP being the energy currency_
How many ATP is produced in stage 4 of aerobic metabolism?
produces water and 34 ATP
What are the four control points in aerobic metabolism of glucose?
- amount of glucose taken up by cell is limigted by insulin
- ATP exerts -ve feedback inhibition of enzymes
- Citrate iions also exert -ve feedback
- ADP and AMP which activate process become limiting as they are converted to ATP
*Understand the fates of glucose
Where is glycogen stored and what is its main advantage?
- All cells store some, but mainly in liver and muscle
- Adv. is to provide a store of energy that can be accessed quickly
*Understand the fates of glucose
Where glucose is stored as fat, where is the energy supplied from for this process?
Describe this e source
- pentose phosphate pathway
- occurs in liver and fat cells
- on each cycle 6 glucose molecules enter and 5 come out (5-sugar) w/ one CO2 and H
- H atoms can be oxidised to give ATP, but normally used in fat synth.
*Understand the various fates of lipids
What are the 3 possible fates of FFA’s taken up by liver?
- partial breakdown for transport out of liver as smler FFA (catabolism)
- Complete breakdown to provide energy (catabolism)
- conversion to triglycerides for storage (anabolism)
_*Understand the various fates of lipids_
describe fate 1 partial break down for TRANSPORT to other tissues
- Liver breaks down LCFA into SCFA using lipase
- FA carried by protein albumin
- Reffered to as non-esterified FA or NEFA’s
- Ketosis occurs when plasma [] of FFA too high
- liver ketone formation occurs in mitochondria
- ketone bodies can’t be used by liver, can be toxic!
_*Understand the various fates of lipids_
describe fate 2 complete break down to provide ENERGY
- Transport of FFA into mito by carnitine
- beta oxidation occurs -cleavage of two C at a time from FA to give acetyl CoA and 4 H atoms
- A-CoA enters TCA cycle where H atom undergoes oxidative phosph.
- Total ATP yield depends on FFA length
When does the synthesis of triglycerides from CHO occur?
Where does it occur?
List the steps
- When? CHO are present in excess of animal’s energy needs and glycogen storage capacity
- Where? Mainly in liver, also in adipose
- Steps?
- conversion of CHO to a-CoA
- a-CoA converted to FA (mostly 14 - 18C) and subsequently into TG’s
When does synthesis of fat from protein occur?
is this an efficient process?
- when dietary protein is in excess of energy reqs
- highly inefficient
Describe lipoproteins
- main form of lipids in blood
- synthesised in liver
- Classified by density, which refers to relative amont of protein they contain
- high or low density
- HDL’s, LDL’s
*Understand the various fates of proteins
How are protens absorbed?
What are the 3 possible fates of proteins?
- absorbed from gut as aa and sml peptides transported to liver where they have 3 possible fates:
- used to synthesise new protein in liver
- deamination and further mtabolism to provide energy
- pass through liver and enter hepatic vein -excretion
_*Understand the various fates of proteins_
Describe deamination
- Amino group is removed to form a keto acid + ammonia
- ammonia combined w/ CO2 to form urea and water
- Urea enters blood from liver and is excreted by kidneys
- in ruminants may enter urea cycle
- remaining keto acid is converted to energy or stored
*Describe why ruminants are ‘special’ with respect to glucose homeostasis
- very little absorption of glucose from rumen
- ALL glucose for ruminants originates from gluconeogenesis
- PROPRIONATE -only VFA to support glucose production
- most proprio extracted from portal blood by liver
- FA only synthesised in adipose of ruminants
