EXAM 3 NOTES: Cell Biology
4/19/24
Cells need consistent input of energy
from sun
from chemical energy (Cellular respiration)
Mayor sources from chemical energy are sugars and fats
Glucose (glycogen or starch)
Energy release by metabolism captured and stores in activated carrier molecules
ATP, NADH/NADPH/FADH2
Energy that can be utilized to do work is free energy
Energy used by cell to drive a chemical reaction
is called G (Gibbs free energy)
If a substrate (reactant) has more energy than product
energy is released (exothermic)
spontaneous
If product has greater energy than reactant
energy input (endothermic)
not spontaneous
Change in free energy (AG) is the difference in energy between the products and the reactants
energy of the product—energy of the reactant
if AG is negative reaction spontaneous
if AG is positive reaction is not spontaneous
if AG is 0, reaction is in equilibrium
Sucrose-glucose+fructose
ADP+P=ATP
Focus on glucose metabolism to generate ATP to satisfy cell energy demands
in the body stepwise oxidation of sugar in cells capture the energy
Formation of ATP from ADP+P is a type of a phosphorylation reaction
1ff: ATP-ADP-AMP
Three mechanisms by which cells may synthesize ATP (some cells have 3 mechanisms)
1ff: Absorption of sunlight, coupled to ATP synthesis (Phosphorylation)
2ff: Energy from activated carriers (NADH, FADH2) coupled to ATP synthesis (Oxidative Phosphorylation)
3ff: Enzyme catalyzed reactions coupled directly to ATP synthesis- (substrate level phosphorylation) (the most abundant anywhere in the cell)
Sugars and fats
main sources of chemical energy
glycolysis and krebs cycle- major pathways of energy metabolism
when o2 available, 40-50% of energy may be captured and stored in ATP
Citric acid cycle=Krebs cycle
Glycolysis (metabolic pathways to break down glucose)
from 1 glucose to 2 pyruvates
10 reactions (10 enzymes)
in cytosol
it can happen in present or without o2
4ATP produced
2atp used
2nadh produced
FYI- details of the 10 reactions of glycolysis
quick overview of reaction 1,6,7 and 10
1ff: ATP is being used, attaching the phosphate to the sugar (phosphorlyation) which keeps the glucose in the celiff
6ff: NAD+ picks up two high energy electron and bounces with proton creating a NADH —> NAD++2E-+H+-NADH
7ff and 10ff: two reactions where ATP is synthesis
Summary of Glycolysis
glucose- 2 pyruvates
net yield of 2 ATP
2 NADH
Pyruvate is involved in so many cellular reactions, the most important ones in metabolic pathways will be Krebs Cycle (aerobic), lactic acid (anaerobic) and ethanol (anaerobic)
2 pyruvates- 2 lactic acids (2 NADH consumed and NAD+ regenerates)
process called fermentation
happens a lot in muscle when energy needed and not enough oxygen
2 pyruvates- 2 Ethanol +2CO2 (2NADH consumed and NAD+ regenerates)
also fermentation
use in bread and alcohol formation
-*also in cytosol*
Summary of Anaerobic metabolism of pyruvate
occurs in cytosol
occurs in absence of O2.
1 molecule of glucose converted to:
2 lactic acids/2 ethanols + CO2
*net yield: 2 ATP produced/ glucose
4/22/24 BIOENERGETICS -2
Major focus is on glucose as energy sources
glycolysis
anaerobic production of lactate and ethanol/CO2
Oxidation of pyruvate
in mitochondrion
not part of krebs cycle (citric acid cycle)
puruvate—> acetyl CoA
pyruvate dehydrogenase complex is comprised of 3 different enzymes (catalyst)
pyruvate +CoA+NAD—> acetyl- CoA+CO2 +NADH
Activated carriers: NADH, acetyl Coa
Acetyl CoA enters Krebs Cycle (citric acid cycle)
net result: one turn of the cycle produces three NADH, one GTP (ATp), and one NADH2, and release two molecules of CO2.
GTP and FADH2 are active carriers
GTP is generally equivalent to ATP
FADH2 carries high energy e-
All reactions here occur in the mitochondrion (citric acid cycle), because one glucose produces two pyruvates, all reactions here a 2x.
Summary of Krebs Cycle + the Oxidation of pyruvates
2 pyruvates yields 6 co2, 2 gtp/ atp, 8 nadh, 2 fadhs,
co2 releases as waste products
uses atp
fadh2 and nadh transfer high energy electrons to the electronic transport chain
NADH- produced during glycolysis, oxidation of pyruvate, krebs cycle
fadh2- produced in krebs cycle
fadh2 and nadh is transfers high energy electrons to electron transport chain
electron transport chain and oxidative phosphorylation occurs in the mitochondria
FATS AND ENERGY SOURCES
TWO EXAMPLES OF LIPID MOLECULES: Phospholipids and triglycerides
phospholipids: amphipathic
triglycerides: hydrophobic
main components of animal fats and plant cells
3 fatty acid tails
stored fats mobilized for energy prodcution in animals… and subsequently metabolized to generate ATP
BETA- OXIDATION OF FATTY ACIDS- IN MITOCHONDRIA AND PEROXISOME
fats/lipids broken down to fatty acids
fatty acids oxidize to acetyl CoA
nadh/fadh2 also produced
there are 3 different activated carriers
B-oxidation of fatty acids (in mitochondria and peroxisome)
2 carbon fragments removed each cycle
products of beta oxidation
fadh2/nadh/acetyl CoA
BETA- oxidation of fatty acids- *mitochondria*
acetyl coA- enters the citric acid cycle
Nadh: donates electrons to the etc
fadh2: donates electrons to etc
linked to ATP production
BETA- oxidation of fatty acids- *Peroxisomes*
What happens to the products of peroxisome Beta oxidation
Acetyl- CoA: CoA exported to the cytosol
NADH: exported to the cytosol
FADH2: used to form H202
NOT linked to ATP production, therefore no atp synthesis
Organisms store excess food(energy) within cell:
sugars stored as glycogen (animal cells) or as starch (plant cell)
lipids/fats stored as fat droplets
Glycogen, starch, and fats used to store excess food molecules
oxidation of sugars and fats share some common pathways
oxidation of 1 gram of triglycerides produces about twice the atp compared to oxidation of 1 gram of starch/glycogen
Molecules are often involved in several different pathways
glycolysis + citric acid cycle make up small fraction of total cellular metabolism