L31 - Metabolism 1 Flashcards
What is energy produced from?
the breakdown of metabolic fuels: fats, carbohydrates and proteins
broken down to be stored in various parts of the body
further broken down to produce ATP
What is energy input mediated by?
hunger/appetite, satiety, social and psychological factors
What is energy output mediated by?
voluntary physical activity, non-exercise activity thermogenesis, adaptive thermogenesis, basal metabolic rate
How much of our energy output goes into voluntary physical activity?
~20%
What are the characteristics of non-exercise activity thermogenesis and how much of our energy output goes into this?
spontaneous muscle contraction, maintaining posture, walking (ambulation), talking, fidgeting
~15%
What are the characteristics of adaptive thermogenesis and how much of our energy output goes into this?
thermogenic effects of food (diet-induced thermogenesis), uncoupled respiration (cold)
~10%
What are the characteristics of basal metabolic rate and how much of our energy output goes into this?
sustain basic functions such as: macromolecule synthesis and ATP production to maintain essential functions such as respiration, cardiac contraction, kidney and liver functions, brain function
~55%
How does ATP provide energy?
energy is released from hydrolysis of phosphate bonds within ATP
What is ATP hydrolysis and therefore energy release catalysed by?
a class of enzymes called ATPases harness the energy from ATP to drive other chemical reactions that would not otherwise occur
What are some examples of ATPase?
metabolic enzymes involved in anabolic processes that need energy and enzymes promoting transport of solutes across membranes
What does low stores of ATP result in?
enough energy to survive for ~90 seconds
need to continuously restore ATP levels
What is the mechanism of action of cyanide?
inhibits cytochrome c oxidase and prevents ATP synthesis, resulting in impaired contractile force
The complete breakdown of one ATP would produce:
adenosine, three inorganic phosphates and energy
What is metabolism?
chemical reactions that take place in an organism: extract energy from nutrients, use energy for work, store energy for later use and produce heat
What is catabolism?
breakdown of substances to generate energy
What is anabolism?
uses energy to synthesise larger molecules from smaller substances
What are the challenges faced by cells in metabolism?
transport nutrients into cells, store nutrients for times of need, mobilise nutrients from stores when needed, convert nutrient to ATP
Which tissues use glucose preferentially?
lens and cornea; areas of kidney; RBC’s; exercising muscle
brain uses it almost exclusively
What is the distribution of glucose after a meal?
50% to storage and 50% for ATP synthesis
How is glucose transported into cells?
glucose enters and leaves capillaries by simple diffusion through spaces between the cells
glucose is transported into cells by facilitated diffusion; that is, carrier mediated transport
What is facilitated transport of glucose mediated by?
by glucose transporters: GLUT 2 (e.g. liver); gradient driven glucose uptake GLUT 4 (e.g. muscle and adipose tissue); responsive to insulin
How is glucose stored?
stored as glycogen
glucose molecules are added to chains of glycogen for storage
the enzyme glycogen synthase catalyses this reaction
How is glycogen broken down to glucose?
glucose is removed from glycogen to form G-1-P
the enzyme glycogen phosphorylase catalyses this reaction
this can be converted to G-6-P and further broken down through glycolysis for energy production
What is the process of glycogen breakdown known as?
glycogenolysis
How is ATP produced from glucose metabolism?
glycolysis -> pyruvate dehydrogenase reaction -> Krebs cycle -> electron transport chain
What are the characteristics of glycolysis?
occurs in cytoplasm of cells
10 reaction steps
two main functions: immediate energy (ATP) and to generate pyruvate
products: 2 x pyruvate + 2 x ATP + 2 x NADH
What are the characteristics of the PDH reaction?
PDH is a complex enzyme that exists in an inactive and active form
rate-limiting step for carbohydrate metabolism, transfers pyruvate into mitochondria
products: 1 x acetyl CoA + 1 x NADH
What are the characteristics of the Krebs cycle?
occurs within the mitochondrial matrix, 8 reactions
main function is to degrade acetyl CoA to ATP and H+ bound to coenzymes -> H+ and e- are passed into the ETC for oxidative phosphorylation
What is the role of coenzymes?
transfer 2 hydrogen atoms from one reaction to another
What are the products of the Krebs cycle?
2 x ATP, 6 x NADH (= 15 ATP) and 2 x FADH2 (= 3 ATP) formed
net: 20 ATP produced
What are the steps of the ETC?
e- from coenzymes donate e- to ETC -> energy released drives H+ across inner membrane, producing a H+ gradient and potential energy -> ATP synthase drives H+ into the matrix and uses the potential energy to promote ATP synthesis -> e- and H+ combine with 1⁄2 O2 to form water
When do tissues use fat?
most tissues preferentially use fat, especially when energy demand is low
How are fatty acids stored?
as triglycerides
How are fats broken down?
lipolysis is catalysed by enzymes called lipases -> glycerol becomes a glycolysis substrate
How are fatty acids transported into cells?
simple diffusion into the cytosol (medium chain FAs)
protein-mediated transport system (long chain FAs)
e.g. fatty acid translocase translocates from cytoplasm to plasma membranes
How are fatty acids metabolised?
transfer of fatty acid from the cytosol into the mitochondria -> β-oxidation -> Krebs cycle -> ETC
Which enzyme mediates the transfer of fatty acid from the cytosol into the mitochondria?
carnitine palmitoyl transferase (CPT1)
What are the characteristics of β-oxidation?
occurs in the mitochondrial matrix, converts one fatty acyl-CoA to acetyl CoA and reducing equivalents
4 reactions in cycle
net production from one fatty acid (C16:0) ~129 ATP
What are the products of β-oxidation?
each cycle produces 1 x acetyl CoA + 1 x FADH2 + 1 x NADH except last cycle where only 1 x acetyl CoA produced
