The digestive and energy systems - Anaerobic & Aerobic metabolism Flashcards
(27 cards)
Nutrition and Nutrients
- Nutrition: study of nutrients and how the body uses them
- Nutrients: chemicals supplied by the environment that an organism requires to survive
- Macronutrients: required in large amounts; lipids, carbohydrates, and proteins
- Micronutrients: required in small amounts; vitamins and minerals
- Energy value of macronutrients is expressed in heat units called calories (kilocalories)
- Essential nutrients are those that cannot be synthesized by human
cells; some fatty acids, some amino acids, and some vitamins are essential
Metabolism
- Catabolism: energy-releasing process where large molecules broken down to smaller
- Anabolism: energy-requiring process where small molecules joined to form larger molecules
- Energy in carbohydrates, lipids, proteins is used to resynthesise ATP through oxidation-reduction reactions
Energy Needs in the Human Body
- Mechanical work: Movement requires muscle contraction
- Chemical work: Anabolism and
catabolism require energy (make up the cells and tissues of the body) - Transport work: The active transport of substances around the body requires energy
Body Stores of Fuels and Energy
Carbohydrates (1g = 4 kcal)
Fat (1g = 9 kcal)
Protein (1g = 4 kcal)
Alcohol (1 g = 7 kcal)
Organs of the Digestive System
Accessory organs:
- Salivary glands
- Liver
- Gallblader
- Pancreas
Alimentary canal:
- Mouth
- Pharynx
- Esophagus
- Stomach
- Small intestine
- Large intestine
- Rectum
- Anus
Stages of the Digestive System
Gastrointestinal (GI) Tract
- Ingestion - Occurs when
material enters via the mouth - Mastication – Improves transit through the GI tract
- Propulsion & Mixing –
Deglutition (swallowing)
& peristalsis, segmental
contractions - Digestion - Chemical breakdown of food into small organic compounds for absorption
- Secretion - Release of water acids, buffers, enzymes & salts by epithelium of GI tract and glandular organs
- Absorption - Movement of organic substrates, electrolytes, vitamins & water across digestive epithelium
- Excretion - Removal of waste products from body fluids
Movement of Digestive Materials: Peristalsis
Movement by muscular layers of digestive tract called peristalsis:
- Consist of visceral smooth muscle
Mixing of Digestive Materials: Segmental
contractions
1) A secretion introduced to digestive tract or food
2) Segments of digestive tract alternate between contracting and relaxing
3) Material in the intestine is spread out and both directions from the site of introduction
4) Secretion or food becomes more spread out in digestive tract and becomes more diffuse with time
Glucose Absorption
- Occurs in small intestine via sodium-dependent glucose cotransporters
- Absorption of glucose in blood circulation enables uptake into required organs via specific transporters
Lipids
- Include triglycerides, phospholipids, steroids, fat-soluble vitamins
- Bile salts surround fatty acid and glycerol to form micelles
- Chylomicrons enter blood stream and travel to adipose tissue
Amino Acid (Protein) Absorption
- Absorbed by symport intestinal epithelial cells
- Symport is driven by a sodium gradient by Na+-K+ pump
- Amino acids move out of intestinal epithelial cells
- Amino acids enter the capillaries of the villi and carried to the liver
ATP – Energy currency in the body
- Adenosine Triphosphate (Adenosine and three phosphates)
How do we use ATP?
- Stored energy is within the bonds
- Enzyme ATPase breaks this bond
- Energy is released and can be used to do “work”
1)ATP hydrolysis (within water) occurs
2) Enzyme ATPase breaks the bond between a Pi molecule
3) ADP is now present
4) Energy released
Anaerobic Metabolism
- Metabolism that resynthesizes ATP without aerobic respiration
- Occurs mainly when there is a requirement for high ATP resynthesis rates
- Energy needs met by 3 anaerobic sources:
1) ATP hydrolysis
2) ATP-PCr system
3) Anaerobic breakdown of glucose or glycogen
ATP-PCr System
- Enzyme Creatine Kinase (CK) facilitates the release of energy from Creatine Phosphate/Phosphocreatine (PCr) i.e. separation
of Pi from Creatine (catabolism) - Energy released then used for the synthesis of ATP from ADP and Pi (ANABOLISM)
Stages:
1) Rest
2) Energy release
3) Phosphocreatine breakdown
4) Resynthesis
- Provides energy for muscular contraction at the onset of exercise and during short term, high intensity activity
- Steady decline in PCr during the first few seconds of maximal activity coupled with the maintenance of ATP
- PCr resynthesises (and for some time maintains) ATP - This however is limited (ATP-PCr stores last 3-15s)
- They deplete when exhausted
- ATP-PCr converts to gylcolysis
Mitochondria
- Mitochondria “Engine room” of a cell. Site for
ATP (re)synthesis:
1) Outer membrane
2) Intermembrane space
3) Inner membrane
4) Cristae
5) Matrix
Anaerobic Glycolysis
- Energy Supply
limited - Following
the 10 reactions
3mols of ATP are
formed (2mol in
Glucose) - Glycolysis stops
in the absence of
O2 due to build up
of Lactic Acid - Lactic Acid
releases H+ Ions
leading to fatigue
Aerobic Metabolism
- Occurs in the presence of O2
- Also known as oxidative phosphorylation
- Can utilise Carbohydrate, Fat, or Protein to resynthesise ATP directly, and generate cofactors e.g., NADH and FADH for later use by enzymes to
generate ATP - It begins with:
1) Glycolysis (Carbohydrate) – can also be anaerobic
2) To generate Aceytl-CoA from pyruvate
3) Progresses into Krebs/Citric acid cycle
4) Finishes with Electron Transport Chain (ETC)
Glycolysis yield
- Glycolysis is first part of
carbohydrate metabolism - Glucose broken down
into two pyruvate - Major steps:
1) Input of ATP: 2 ATP used to make glucose more
reactive
2) Sugar cleavage: fructose-
1,6-bisphosphate is cleaved into 2 3-carbon molecules
3) NADH production
4) ATP and pyruvate
production - Final products from one
glucose = 4 ATP, 2 NADH, 2 pyruvate
Acetyl Co-A Synthesis
- At the end of Glycolysis we get Pyruvate and a small amount of energy (2 ATP) and electron carriers (2 NADH)
- There is still plenty of potential energy in the chemical bonds of
pyruvate - Pyruvate has one of two fates now – either it continues without
oxygen, in the cytosol and is fermented anaerobically
OR
- It can be converted to Acetyl Co-Enzyme A and continue to the TCA cycle. To do that Pyruvate must enter the Mitochondria
Stage 1.1: Forming of acetyl-CoA
Purpose:
- To allow pyruvic acid to enter the citric acid cycle
- Does not produces ATP but does release 2 NADH
- Produces 2 CO2
Location:
- Mitochondrial matrix
Crucial step:
- Irreversible
Lipid Metabolism
- Adipose triglycerides are
broken down and released
as free fatty acids - Free fatty acids are taken
up by cells and broken
down by beta-oxidation
into acetyl-CoA which:
1) Can enter krebs (citric acid) cycle
2) Can be converted to ketone bodies (ketogenesis) in liver. Ketones travel to skeletal muscle and are used in citric acid cycle to produce ATP
Stage I: Glycolysis
Purpose:
- 1 molecule of glucose is degraded to 2 molecules of
pyruvate
Crucial steps:
- 10 chemical reactions that requires 2 molecules
of ATP
1) Input of ATP
2) Sugar cleavage
3) NADH (Nicotinamide adenine dinucleotide) production
4) ATP and pyruvic acid production
- Oxygen does not participate directly at this stage but the presence of O2 determines fate of pyruvic acid at the end of glycolysis
Location:
- Sarcoplasm (cytosol)
Start point:
- Glucose
End point:
- Pyruvate (aerobic H), Lactate (anaerobic X), NADH and ATP
Small number of ATP:
- 4 ATP created but also uses 2 ATP, so net profit of 2 ATP
Stage 2: Krebs cycle
Purpose:
- Acetyl-CoA is degraded to hydrogen atoms (H+) and
CO2
Crucial points:
- Does not produce much ATP, but ‘strips’ the H+ to combine with NAD or FAD2 (flavin adenine dinucleotide) for use in electron transport chain
- O2 does not participate directly
Location:
- mitochondria
Start-point:
- Acetyl-CoA
Eight reactions…
End-point:
- Oxaloacetate (then back to Acetyl-CoA)
Products:
- 3 molecules of NADH + 1 molecule of FADH2;
= Four pairs H+ for use by NAD+ and FAD2 in electron
transport (i.e. 8 H+ per turn)
Relatively small number of ATP:
- 1 ATP per turn
