3. Energy and carbohydrates 1 Flashcards
Define metabolism
Metabolism is the set of processes which derive
energy and raw materials from food stuffs and use
them to support repair, growth and activity of the
tissues of the body to sustain life
Describe an overview of metabolism
- Food comes in through the GI tract
- Broken down to smaller molecules
- Absorbed into the blood where they are transported to tissues that require them
- In the tissues either used directly to release energy within them or interconverted into synthetic pathways to make larger molecules perhaps for storage, eg to make other proteins from the proteins that were digested.
What are the two metabolic pathways?
- Catabolic pathways
2. Anabolic pathways
Describe catabolic pathways
1.Break down larger molecules into smaller ones
(intermediary metabolites)
2.Release large amounts of free energy
3. Oxidative – release H atoms –‘ reducing power’
Describe anabolic pathways
- Synthesis larger important cellular components fro intermediary metabolites
- Use energy released from catabolism (ATP)
- Reductive(ie use H released in catabolism)
Do all metabolic pathways occur in all cells?
No
- Some metabolic pathways occur in all cells
- Others are restricted to some cell types
- Some may be further restricted t compartments within cells
In catabolic metabolism, what are the fuel molecules metabolised to supply?
- Building block material
- Organic precursors
- Biosynthetic reducing power
- Energy for cell function
Give 3 examples of building block material
- Sugars
- Amino acids
- Fatty acids
What are the building block materials produced in catabolic metabolism used for?
- Dynamic state of cell components (turnover)
- Cell growth and division
- Repair
Give an example of an organic precursor?
Acetyl CoA
Give two examples of biosynthetic reducing power
- NADH
2. NADPH
Define energy
Capacity to do work
What sort of work is energy needed for?
- Biosynthetic work (anabolism) - synthesis of cellular components
- Transport work - membranes
- Specialised functions
Give two examples of transport work
- maintenance of ion gradients (Na+,K)
2. Nutrient uptake
Give 3 samples of specialised functions
- mechanical work- muscle contraction
- Electrical work - nervous impulse contraction
- Osmotic work - kidney
What is the standard international unit for energy content for food?
Joule
What does a calorie generally mean?
1 kcal
What is basal metabolic rate?
Energy required by an awake individual during physical, digestive and emotional rest at 18oC
Sum of energy used by all of the tissues in the body
When energy intake (FOOD) > energy required, then what is the excess energy used for?
- Growth - synthesis of new tissue
2. Stored - production of adipose tissue
Which form f energy is predominantly used to drive energy requiring activities?
Chemical bond
Define exergonic
A chemical reaction which releases energy
Define Endergonic
Chemical reactions which require energy
Which reactions occur spontaneously?
Exergonic reactions
In which reactions are deltaG negative?
Exergonic
In which reactions are deltaG positive ?
Endergonic
Define oxidation
Removal of electrons or removal of H atoms
Define reduction
Gain of electrons or H atoms
When fuel molecules are oxidised, the electrons and protons are transferred to what?
Carrier molecules eg NAD, NADP
Carrier molecules act as carriers of reducing power for which processes?
- ATP production(NADH)
2. Biosynthesis(NADPH)
How many H atoms are added to the carrier molecules?
2 and 1 dissociates into solution
How can energy released as reducing equivalents be used to drive energy requiring activities?
1.Directly, e.g. use of NADPH in biosynthesis 2.Indirectly, e.g. mitochondrial system to couple NADH to the production of ATP
What is the energy released during exergonic reactions used to drive?
ATP production -Part of the free energy conserved as the chemical bond energy of the terminal phosphate group (PO
44-) of ATP
Can ATP be used as a store of energy
NO - only a carrier, not a store
What feature of ATP makes it very good as a carrier molecule
It is stable -does not break down
When ATP is high, which pathways are activated
Anabolic
When ATP levels are low and ADP and AMP levels are high which pathways are activated?
Catabolic
Which enzyme is used to produce ATP and AMO using 2ADP when ATP levels are really low?
Adenylate kinase
Which forms is energy stored as ?
Glycogen, triglyceride
Which is a high energy store that can be used immediately?
Creating phosphate
Describe the process by which energy is stored as phosphocreatine including the enzyme used.
When energy supply exceeds demand, ATP combines with creatine in the presence of the enzyme creatine kinase to form ADP and phosphocreatine. Thus, the phosphate bond energy can be stored in phosphocreatine. When ATP levels are low, he phosphocreatine can combine with ADP to form ATP and creatine
What is creatine kinase a marker of and why?
Myocardial infarction - CK is released from cardiac myocytes (cells) into blood when damaged, in myocardial infarction (heart attack).
What does creatine and phosphocreatine spontaneously break down into?
Creatinine
How can you obtain a measure of muscle mass and why?
Measuring levels of creatinine in urine as creatinine is only stored in skeletal muscle. Creatinine excretion per 24h is proportional to muscle mass of the individual
– Provides a measure of muscle mass
Creatinine is produce by a —1— reaction at a —2— rate.
Cill in the gaps
- Spontaneous
2. Constant
Creatinine concentration in urine is a marker of what?
Urine dilation - if creatine concentration is high suggests dehydrated. And vice versa. Can be used to estimate true urinary loss of many substances
What is metabolism?
Inter conversion of biological molecules in small chemical steps
What process is used to convert reducing power to ATP
Oxidative phosphorylation
Catabolism involves the breakdown of chemicals to release?
- Reducing power(NADH,NADPH,FAD2H)
2. Energy(ATP)
What is stage 1 on catabolism and what is its purpose?
Breakdown of fuel molecules to building block molecules
Purpose - to convert
nutrients to a form that can
be taken up into cells.
Where does stage 1 of catabolism occur and where do the products end up?
Extracellular (GI tract) - Building block molecules
absorbed from GI tract into
circulation
Is any energy released in stage 1?
No
What bonds are broken in stage 1 of catabolism?
Breakage of C - N and C - O bonds (no C - C)
What is stage 2 of catabolism?
Degradation of building block materials to metabolic intermediates and a small number
of organic precursors
(Glycolysis)
Where does stage 2 occur?
Intracellular
cytosolic & mitochondrial
Is energy released in stage 2?
Small fraction of energy released
What bonds are broken in stage 2?
C - C bonds broken
What kind of a process is stage 2?
Oxidative -release of ‘reducing
power’ (NADH) and some
‘energy’ (ATP)
What can be said about the pathways of stage 2?
Many pathways
What is stage 3 of catabolism?
Krebs cycle
- Acetyl coA oxidised to CO2
(produces precursors
for biosynthesis)
Where does stage 3 occur?
Mitochondria
Is energy released in stage 3?
Small fraction of energy released
What can be said abut the stage 3 pathway?
A single pathway –
Tricarboxylic acid (TCA)
cycle
What type of process is stage 3?
Oxidative
What is stage 4 of catabolism?
Electron transport and oxidative phosphorylation
Where does stage 4 occur?
Mitochondria
Does stage 4 release energy
- Energy released
* ATP synthesised
What molecule does stage 4 require
Oxygen
Which 4 cells have an absolute requirement for glucose?
- Red blood cells
- Neutrophils
- Innermost cells of kidney medulla
- Lens of the eye
What are the enzymes involved in stage 1? Include where they are found and what they break down.
>Amylase - saliva (starch,glycogen) >disaccharidases - attached to brush border membrane of epithelial cells in small intestines • lactase (lactose) • sucrase (sucrose) • Pancreatic amylase (a1-4 bonds) • isomaltase (a1-6 bonds)
Why isn’t cellulose (b 1-4 bonds) digested in the human body?
Alpha and beta glycosidic bonds are different. Amylase can recognise the structure of alpha glycolic bonds but cannot recognise the beta bonds in cellulose so cannot break cellulose down
What is lactose intolerance?
Lactose intolerance is when the body does not produce the enzyme lactase to break down and digest lactose. Therefore, lactose remains in the small intestines causing concentration in the small intestines to increase so water moves in casing diarrhoea
What is primary lactase deficiency and who does it currently in?
- Absence of lactase persistence allele.
* Only occurs in adults
What is secondary lactase deficiency caused by and who does t occur in?
- Caused by injury to small intestine:
- Gastroenteritis
- Coeliac disease
- Crohn’s disease
- Ulcerative colitis
• Occurs in both infants & adults
• Generally reversible
foods
What causes congenital lactase deficiency?
• Extremely rare, autosomal recessive defect in
lactase gene.
Cannot digest breast milk.
What are the symptoms of lactose intolerance?
Symptoms: • Bloating/cramps • Flatulence • Diarrhoea • Vomiting • Rumbling stomach
How are monosaccharides absorbed into the blood?
• Active transport (low to high concentration) into intestinal epithelial cells by
sodium‐dependent glucose transporter 1 (SGLT1) then,
• Passive transport (high to low concentration) via GLUT2 into blood supply
How is glucose in blood transferred to cells?
Glucose uptake into cells from blood is via facilitated
diffusion using Glucose transporter proteins (GLUT1 - GLUT5).
Where is glut 1 found?
In mostly all cells but mainly in Fetal tissues, adult erythrocytes, blood–brain barrier.
Where is GLUT 2 found?
Kidney, liver, pancreatic beta cells, small intestine
Where is GLUT 4 found?
Adipose tissue, striated muscle *insulin-regulated
What are the functions of glycolysis
• Oxidation of glucose • NADH production (2 per glucose) • Synthesis of ATP from ADP (net= 2 ATP per glucose) • Produces C6 and C3 intermediates
What are the 6 features of glycolysis?
• Central pathway of CHO catabolism • Occurs in all tissues (cytosolic) • Exergonic, oxidative • C6 -> 2C3 (No loss of CO2) • With one additional enzyme (LDH), is the only pathway that can operate anaerobically • Irreversible pathway
Why are there so many steps in glycolysis?g
- Chemistry easier in small stages
- Efficient energy conservation
- Gives versatility
• allows interconnections with other
pathways
• allows production of useful
intermediates
• allows part to be used in reverse - Allows for fine control
What happens in stage 1 of glycolysis and why is it done?
Phosphorylation of glucose to glucose-6-
phosphate (G-6-P). ATP —> ADP
• Makes glucose negatively charged (anionic) 1 ADP • Prevents passage back across the plasma membrane Glucose-6-P • Increases the reactivity of glucose to permit subsequent steps
What happens in rage 2 of glycolysis?
Glucose-6-P converted to fructose-6-P
What happens in stage 3 of glycolysis?
Fructose-6-P phosphorylated to fructose 1,6-bis-P.
ATP —-> ADP
What kind of step is step 3 of glycolysis?
Committing step: first step that commits glucose to metabolism via glycolysis
What happens in step 4 of glycolysis?
Cleavage of C6 into two C3 units (DHAP and glyceraldehyde 3-P)
What happens in step 6 of glycolysis?
Small amount of reducing power captured (NADH).
Glyceraldehyde -P ——> 1,3-bis phosphoglycerate
What happens in step 7 and 10 of glycolysis?
ATP synthesis
• 1,3-BPG and PEP(phosphoenolpyruvate —> pyruvate)
• Transfer Pi to ADP to give ATP
• ‘Substrate level phosphorylation’
Which steps of glycolysis are reversible?
Steps 1,3 and 10 because have large negative deltaG values
How can glycolyissi be used in diagnosing cancer?
Rate of glycolysis up to 200 times greater in cancer. Measure uptake of 2-18F-2-deoxyglucose (FDG) (Radioactive glucose mimicking substrate )
