Ch 5 Flashcards
Anabolism
requires the input of energy to synthesize large molecules
“building something up”
Catabolism
releases energy by breaking down large molecules into small molecules
“breaking something down”
Catabolism drives anabolism
The catabolic reactions that break down glucose, fatty acids, and amino acids serve as ENERGY SOURCES for the anabolism of ATP.
aerobic cellular respiration
Complete catabolism of glucose requires oxygen as the final electron acceptor.
But…breaking down glucose requires many enzymatically catalyzed steps, the first of which are anaerobic
Glycolysis (general)
conversion of glucose into two molecules of pyruvic acid
–> no oxygen needed
Glycogenesis
production of glycogen (mostly in skeletal muscles and liver)
Glycogenolysis
hydrolysis (breakdown) of glycogen
–> yields glucose 6-phosphate for glycolysis or free glucose that can be secreted in the blood
Gluconeogenesis
production of glucose from noncarbohydrate molecules, including lactic acid and amino acids, primarily in the liver
Lipogenesis
the form of triglycerides (fat), primarily in adipose tissue
Lipolysis
hydrolysis (breakdown) of triglycerides, primarily in adipose tissue
Ketogenesis
formation of ketone bodies, which are 4-carbon long organic acids, from fatty acids, occur in the liver
Three steps in aerobic respiration of glucose
- Glycolysis: occurs in cytoplasm, anaerobic
- Citric Acid (Krebs) Cycle: occurs in matrix of mitochondria, aerobic
- Electron Transport: occurs in cristae of mitochondria inner membrane, aerobic
- -> where we get the MOST ATP
Glycolysis (detailed)
• First step in catabolism of glucose
• Occurs in the cytoplasm of the cell
• Glucose is split into two pyruvic acid molecules
• 6-carbon sugar–> 2 molecules of 3-carbon pyruvic acid
• C6H12O6 –> 2 molecules C3H4O3
——> (don’t need to know structure, just that it moves from one 6-carbon to two 3-carbon)
• Note loss of 4 hydrogen ions. These were used to reduce
2 molecules of NAD (2NAD + 4H+ –> 2NADH+ H+(2NADH))
——> no need for oxygen
Glycolysis equation
Glucose + 2 NAD + 2 ADP + 2 Pi –> 2 pyruvic acid + 2 NADH + 2 ATP
(4 hydrogens reduced to 2 in product)
pyruvic acid –> used in citric acid cycle
NADH –> oxidized to make ATP
Lactic Acid Pathway
When there is NO oxygen to complete the breakdown of glucose, NADH has to give its electrons to pyruvic acid.
- ->This results in the reformation of NAD and the conversion of pyruvic acid to lactic acid.
- anaerobic metabolism/lactic acid fermentation
- net yield of 2 ATP
muscle cells
can survive for awhile without oxygen by using lactic acid fermentation
RBCs
only use lactic acid fermentation because they lack mitochondria
Citric Acid Cycle
Acetyl CoA (from pyruvic acid) + oxaloacetic acid = citric acid
- citric acid moves through reactions to produce more oxaloacetic acid
- -> One GTP is produced, which donates a phosphate group to ADP to form ATP
- 3 molecules NAD –> reduced to NADH
- 1 molecule FAD –> reduced to FADH2
- **events occur for each acetic acid, so it happens twice for each glucose molecule
Citric Acid Cycle: for each glucose we produce…
- 6 NADH
- 2 FADH2
- 2 ATP
- 4 CO2
Electron Transport & Oxidative Phosphorylation
- molecules in the cristae (folds) of the mitochondria act as electron transporters
- -> they accept electrons from NADH and FADH2 (produced in Krebs Cycle). H+ NOT transported.
- -> Oxidized FAD and NAD are reused
Electron Transport Chain
Electron transport molecules pass the electrons down a chain, with each being reduced and then oxidized
- exergonic reaction: energy produced - ADP –> ATP
- -> ADP experienced (direct) oxidative phosphorylation - less than 50% efficient (some released as heat)
Oxidative Phosphorylation Steps
- Electron transport fuels proton pumps
- H+ pumped from the mitochondrial matrix –> space between the inner/outer membranes - Creation of a huge concentration gradient between membranes
- H+ can ONLY move through the inner membrane through structures called respiratory assemblies
- Movement of H+ across the membrane provides energy to the enzyme ATP synthase, which converts ADP to ATP.
Why is the mitochondrial outer membrane important?
**no outer membrane would mean the H would diffuse into cytosol = no concentration gradient, outer membrane is important to get max ATP!!
Oxygen
- Final electron acceptor
- citric acid cycle/electron transport require oxygen
Water is formed in the following reaction: O2 + 4e- + 4H+ –> 2H2O
Where do we get our total ATP?
Direct (substrate-level) phosphorylation in glycolysis + citric acid cycle = 4 ATP
Oxidative Phosporylation = varying amounts of ATP (32-34)
–> Theoretical ATP yield is 36-38 per glucose, but actual yield is 30-32 ATP per glucose b/c energy is needed to move ATP from mitochondria to cytoplasm
Glycogenesis
- Cells can’t store much glucose because it will pull water into the cell via osmosis.
- Glucose is stored as a larger molecule called glycogen in the liver, skeletal muscles, and cardiac muscles.
- Glycogen is formed from glucose via glycogenesis.
Glycogenolysis
• When the cell needs glucose, it breaks glycogen down again.
• Produces glucose 1-phosphate (cannot leave muscle or heart cells)
–> The liver has an enzyme called glucose 6- phosphatase that removes the phosphate so glucose can reenter the bloodstream
• Glycogen phosphorylase is the catalyst (breaks it down)
Glycogenolysis: liver
brain is glucose dependent, but doesn’t store it well
liver stores the glucose as glycogen —> breaks it down and sends it into the blood where it can get to the heart
The Cori Cycle
exchange of lactic acid between skeletal muscles and liver
SKELETAL MUSCLE: glycogen –> glucose –> pyruvic acid –> lactic acid
*lactic acid enters bloodstream
LIVER: lactic acid –> pyruvic acid –> glucose
*glucose enters bloodstream
Why do you need to warm down after a workout?
so you can keep the blood flowing and wash the lactic acid out of the skeletal muscles
Lipid and Protein Metabolism
- can be used for energy by same pathways as metabolism of pyruvic acid
- excess food energy (glucose) is then stored as glycogen/fat (none is stored as ATP)
Lipid Metabolism
- ATP levels rise –> ATP production inhibited
- Glucose doesn t complete glycolysis to form pyruvic acid
- -> Acetyl CoA already formed is joined together to produce a variety of lipids, including cholesterol, ketone bodies, and fatty acids.
- lipogenesis
Lipogenesis
Fatty acids combine with glycerol to form triglycerides in the adipose tissue and liver
–> making fat, in fat cells, in times of excess (intake exceeds immediate energy requirements)
Fatty Acids as an Energy Source
β-oxidation: Enzymes remove acetic acid molecules from fatty acids to form acetyl CoA
- For every 2 carbons on the fatty acid chain, 1 acetyl CoA can be formed.
- Each acetyl CoA –> 10 ATP + 1 NADH + 1 FADH2 (decent yield of ATP)
Acetyl CoA can turn into….
- cholesterol (steroids, bile acids)
- ketone bodies
- citric acid cycle (CO2)
- fatty acids (triglycerides, phospholipids)
Amino Acid Metabolism
-provides nitrogen for body
-Amino acids from dietary proteins are needed to replace
proteins in the body (we can only make 12/20)
–>essential AA: from diet
-If more amino acids are consumed than are needed, the excess amino acids can be used for energy or converted into carbohydrates or fat
Amino Acids as Energy
different amino acids enter in at different places/times to drive the reactions
(none funnel in during glycolysis)
—> can use AA to funnel in for energy
Energy Sources
- LIVER: Glucose and ketone bodies
- ADIPOSE TISSUE: Fatty acids
- MUSCLE: Lactic acid and amino acids
Energy Sources: Brain
brain requires lots of glucose, little ketone bodies (can’t use fatty acids/lactic acid)
–> why it’s important to keep blood glucose levels regular
