Energy & Cellular Metabolism Flashcards
chemical composition of animals
carbon = predominant molecule
organic molecules
-carbon bonds saturated with oxygen or hydrogen
-nitrogen participates in structure and function of molecules
major molecules of animals
- carbohydrates: 1% of body weight: C,H,O
- lipids: 15% of body weight: C,H,O
- proteins: 17% of body weight: C,H,O,N
- nucleic acids: 2% of body weight: C,H,O,N
what makes up the other 55-65% of body mass?
water
metabolism
sum total of an organism’s biochemical reactions
- catabolism
- anabolism
catabolism
breakdown of organic molecules into simpler compounds to release the energy stored in chemical bonds
-complex -> simple
anabolism
synthesis of organic molecules required for
- cell structure
- function and
- storage of energy
- simple -> complex
- building, resynthesizing, making larger and more complex molecules
released energy is utilized to perform cellular work and physiological processes
- biochemical work: anabolic and catabolic reactions
- transport work: transport of material across plasma membrane or epithelial lining
- mechanical work: generate force and movement - beating of cilia, contraction of muscles and movement of chromosomes , any movement in the body ex.cell division will consume energy
- repair and maintenance: renewal of cells
flow of chemical energy
- ADP +Pi + energy from food -> ATP glycolysis and Krebs cycle
- ATP -> ADP + Pi + energy available for cellular functioning
how do plants store glucose?
starch
how do humans store glucose?
glycogen
energy hierarchy
- glucose
- breakdown of glycogen
- lipids
- protein resources
- nucleic acids
- note: under normal conditions, never going to kill cells to get nucleic acids energy
metabolizing
- when metabolizing these molecules, end up with CO2 and H2O
- when metabolizing proteins, generate ammonia/nitrogen products
- ammonia is toxic (nitrogenous waste)
energy requiring cell functions
- force and movement
- active transport across membranes
- molecular synthesis
where is energy stored and released?
energy is stored in chemical bonds and energy is released when bonds are broken
energy storage molecules
stable molecules such as sugars, starch, glycogen, fats and proteins
energy carriers
NADH (reduced form captures energy) NAD+ (oxidized form releases energy) FADH2/FAD -most versatile is ATP -capture energy for short time -hydrolyze so that energy can come out
Why is ATP a suitable molecule for this purpose (good energy carrier molecule not storage)?
- because of its structure
- covalent bonds provide stability
- negative charges (oxygen) provide instability: neg charges close -> pull away from each other, easy to fall apart
- stability/instability of ATP structure makes it an ideal molecule for quick release of energy
- ATP/ADP + Pi -> recyclable in any physiological scenario
- bonds break: energy released
- ATP moves backwards for ATP synthesis
order of preference as fuel
- glucose: 1st choice for substrate
- glycogen
- fats-fatty acids and triglycerides: don’t convert to pyruvate
- proteins: some amino acids convert to pyruvate- gluconeogenic pathway
- nucleic acids
glycerol
glycerol is an alcohol which can convert to pyruvate which can covert to glucose
-gluconeogenic pathway
energy metabolism
- oxidative metabolism: glycolysis and oxidative phosphorylation
- when proteins are phosphorylated, they are typically activated
- intermediary metabolism: big web of metabolism - glucose, protein metabolism
- mix of catabolic and anabolic activity
- not exclusive of each other
review: energy metabolism
- glycolysis
- krebs cycle
- electron transport system
- oxidative phosphorylation
glycolysis
- first step in energy metabolism
- no oxygen needed
- occurs in cell cytoplasm
- substrate: 1 glucose
- end product: 2 ATP + 2 pyruvate
glycolysis: pros and cons
- low energy yield: yields only 2 ATP compared to TCA cycle where 2 pyruvates (of glycolysis) yield total 36 ATP
- ATP production rate is fast: glycolysis (oxidative metabolism) preferred when immediate energy is needed
- does not need oxygen: body depends on ATP in early phases of INC demand for energy, oxygen comes towards end of process, even before we INC rate of respiration - glycolysis can of on and help us with 2 ATP
more 02 needed for cellular respiration
at times, we reach level of activity where we can’t breathe as hard as we need too -> greater demand for O2 in tissues, rate of respiration does not match demand - low O2 environment -> depend on glycolysis
low oxygen conditions (over-exercise)
muscle cells depend on glycolysis
- lactic acid build up may cause muscle fatigue/pain
- ultimately lactic acid is converted back to pyruvate in the liver - gluconeogenesis
- in presence of 02 (aerobic condition), pyruvate moves to the Krebs cycle
- yeast and bacterial fermentation results in ethanol production
oxidative metabolism is always there, always breathing
-shifts: depending more on glycolysis and less on oxidative respiration when?
when rate of respiration does not match cellular demand for 02 -> more pyruvate is building up -> muscles ache the next day -> pyruvate converts to lactic acid -> accumulates in muscle cells -> destruction, slowing of activity -> pain in muscles bc day before cells not getting enough o2 -> muscle cells depend more on glycolysis than Oxidative metabolism -> end product is lactic acid buildup in muscle
Should you exercise the day after a workout when you are sore?
yes, the lactic acid in muscle buildup needs to go to liver and convert to pyruvate -> want to get rid of lactic acid from muscle -> more blood flow -> use muscles (similar activity at lower level intensity) -> inc blood flow -> lactic acid gets out of muscle to liver -> converts to pyruvate (gluconeogenesis)
formation of acetyl coA
see diagram
Krebs cycle
- occurs in mitochondrial matrix
- amphibolic pathway: any chunk of processes can occur at any time, accumulation of catabolic and anabolic
- energy carrier molecules (NADH and FADH2) are produced that pass electrons to the electron transport system are produced
do we use glycolysis to meet our physiological needs?
yes
does pyruvate always enter TCA/Krebs cycle?
no, because can convert to lactic acid
election transport system/chain (ETS/ETC)
- occurs on inner mitochondrial membrane
- four protein complexes (1,2,3,4) and two electron carriers (ubiquinone and cytochrome c) make ETS
- electron are transferred from electron donors to electron acceptors through REDOX REACTIONS (both oxidation and reduction occurring simultaneously)
- electron transfer is coupled with the transfer of protons (H+ ions) across mitochondrial membrane, creating an electrochemical proton gradient
- at the “bottom”, oxygen captures the electrons and H+ to form water
- the gradient drives the synthesis of ATP
as electrons move from protein to another, protons are produced
-protons accumulate in inter membrane space
in the last protein of ETC chain
- protons produced and o2 present in cells (coming from the air we breathe)
- o2 gets absorbed in blood and goes to tissues
- o2 enters tissue
- this o2 is required in last reaction (when o2 and protons interact) -> water and co2 produced
chemiosmosis
the coupling of the electron transport chain to ATP synthesis
ATP Synthase
- the protein complex ATP synthase in the crustal is the only place where H+ diffuses back to the mitochondrial matrix
- as hydrogen ions flow down their gradient, they cause the cylinder portion and attached rod of ATP synthase to rotate
- the spinning rod causes a conformational change in the knob region, activating catalytic sites where ADP and inorganic phosphate combine to make ATP
ATP Synthase CONT
- facilitate synthesis of ATP
- provides channel, opening for protons to pass through
- channels work according to concentration gradient
- protons move into mitochondrial matrix -> conformational change in intracellular domain (cytosol) -> ATP synthase activation
inner membrane of mitochondria
- ETC located
- ATP synthase protein embedded
if o2 need not met, depend on glycolysis
oxygen at the end of the process is an important regulator of metabolism picture
- makes us breathe at faster rate
- more exercise = more water produced
- metabolic water produced -> cellular water
role of enzymes and hormones in metabolism
hormones and enzymes regulate metabolism by determining:
- when the rate of reaction will change
- where it will take place, tissue specific
- which substrates are we going to use, how long the switch will take place
- hormones act at the broader level of regulation (global)
- hormones regulate enzyme activity
- enzymes regulate specific biochemical steps in the pathway of energy generation
enzyme action
- enzymes are catalysts only: do not initiate rxn or pathway, they simply make the environment more conducive for activity to take place
- enzymes are substrate specific
- enzymes lower the activation energy requirement by:
- > substrate orientation/presentation (bring molecules closer)
- > weakening the bonds in substrate molecule
- > providing a conducive micro environment
activation energy
the Ea needs to metabolize these substrates is higher than the energy that is available in our environment
-once Ea req is lowered then activity takes place
glucose- 2 scenarios
glucose enters the cell -> plasma membrane
- if no excess energy: converts gluco 6 phosphate to glucose
- if energy demand is high -> converts to pyruvate
hexokinase
gets activated and promotes conversion of glucose to glucose 6 phosphate
phosphofructokinase
moves the reaction forward and no stopping until last reaction
pyruvate kinase
- last regulator
- activity depends on how much pyruvate accumulated
- too much pyruvate: backwards reaction will slow down
3 enzymes play key role in regulating rate of glycolysis and fate of gluco-6-phosphate
- move forward in glycolysis or stored as glycogen in cells
- because of influence of hexokinase bc that molecule cannot leave the cell once it is converted to glucose 6 phosphate
glucose 6 phosphate
no transporters for this
phosphorylation
may lead to activation or inactivation of enzymes
-regulated by enzymes
glycogen phosphorylation
-when phosphorylated, it is activated
glycogen breakdown enhanced and promoted
glycogen synthase
- when phosphorylated, it is not active
- inactive form leads to deactivation
- inhibits glycogen synthesis
glycogen synthase (active)
glucose converts to glycogen
glycogen phosphorylase (active)
glycogen converts to glucose
glucagon
- promotes glycogenolysis
- inhibits glycogenesis
enzyme location is tissue specific
ex. only liver contains glucose 6-phosphatase
skeletal muscle ex.
trapped in skeletal muscle cells
- glucose enter cell and hexokinase activated and converts to glucose 6 phosphate
- only that cell is capable of utilizing its own glucose or glycogen bc no transport for glucose 6 phosphate
- 2 options: store as glycogen and use later on or if we need energy, glucose 6 phosphate will enter glycolysis -> production of energy
liver cells are unique
liver cells are the only cells that provide energy to other cells
flow of chemical energy
- heat energy 60% leaves
- 40% of energy goes towards synthesis
UCP1
uncouples oxidative phosphorylation from electron transport chain
- norepinephrine and thyroid hormones are invoved
- H+ diffusing into mitochondria through UCP1 are used for fatty acid metabolism leading to thermogenesis
- uncoupling activity tied together: activity of ETC chain (proton generator), tied to ATP activity synthesis
UCP1 provides channel for proton transfer
- protons moving back into mitochondrial matrix
- less protons moving towards ATP synthesis -> ATP synthesis rate dec-> goes towards fat metabolism -> heat production -> maintains body temp as heat leaves the body
if an animal is feeling cold
cold is a stressor
- stress stimulates production of norepinephrine/epi
- cold temp activates T3/T4 production by acting through TRH/TSH mech
- epi/norepi and T3/T4 stimulate insertion of protein called UCP1 in inner mitochondrial membrane
role of hormones in intermediary metabolism
glycogen synthesis and glycogen breakdown
Glycogen Synthesis and Breakdown
- actively inhibits glycogen breakdown: glycogenolysis
- insulin promotes uptake of glucose and glycogenesis (synthesis of glycogen)
- glucagon and epi: promotes glycogenolysis
glucagon and epinephrine
- promotes glycogenolysis
- inhibits glycogenesis
- these 2 types of hormones act antagonistically: one promoting glycogen synthesis
- together promoting glycogen breakdown
gluconeogenic pathway
pyruvate -> glucose
glucose -> pyruvate
stimulated by hormones like glucagon, cortisol
cortisol and GH
synergistically promote gluconeogenesis: breakdown of protein to promote energy so that glucose can be spared for utilization in brain -> big picture regulated by hormones
reaction regulators determine
- stimulation/facilitation or inhibiting
- rate
- termination (by switching substrates)
reaction regulators
- hormones (global picture)
- enzymes (specific target points)
- reaction substrate (strong reaction regulators)
- reaction product (end products react as regulators)
substrate/pathway preference during varying energy demands
currency: ATP
substrates: creatine phosphate (phosphocreatine), glucose/glycogen/fat/proteins
pathways: creatine phosphate cycle, oxidative pathway, anaerobic pathway
which of the following hormones simultaneous stimulate glycogenolysis (breakdown) and inhibit glycogenesis (synthesis) by phosphorylating enzymes in the same cell?
glucagon
ATP is generated by
- phosphorylation of ADP in cytosol. Pi comes from creatine phosphate
- oxidative phosphorylation (includes glycolysis)
- anaerobic respiration -glycolysis. pyruvate converts to lactic acid
oxygen debt
ATP production to restore homeostatic levels of resources such as creatine phosphate and glycogen
