Cell and Molec Bio (Exam 2)

Carbon Cycle (2)

• describes the flow of carbon atoms on earth

• used to examine how energy is captured and released by living things

What processes make up the carbon cycle? (2)

• photosynthesis

• cellular respiration

Photosynthesis (2)

• processes through which energy from sunlight is captured and used in a two-step process to synthesize energy rich carbon-containing compounds

• reduces CO₂ and uses light energy to push electrons to a high energy state

Cellular Respiration (3)

• collection of metabolic reactions within cells that use O₂ to oxidize and break down food molecules to produce energy in the form of ATP

• results in the release of the light energy from the electrons

• involves orchestration of cellular processes

Oxidation

reactions in which an atom fully or partially loses one or more electrons

Reduction

reactions in which an atom fully or partially gains one or more electrons

Why are oxidation and reduction reactions coupled?

when one molecule is gaining electrons another is losing them

What happens as electrons move to lower states?

they release free energy that will be harnessed for ATP synthesis

What is specifically being transferred in cellular respiration and photosynthesis?

hydrogens, which includes one 1 proton and 1 electron

What is happening to electrons during the multistep oxidation of glucose? (2)

• electrons are moved to lower energy states as they are passed from donor to acceptor through multiple redox reactions

• energy is given off in small packets that can be harnessed by biological systems

What does a multi-step series of redox reactions require?

small inputs of activation energy

What does a one step oxidation of glucose require? (2)

• a lot of activation energy

• energy is given off in a a large burst

How can we ensure that the breakdown of glucose is energetically favorable?

an electron shuttle

Electron Shuttle (2)

• a molecule that can take electrons from one reaction to another

• used to store and transfer energy of electrons

What are examples of an electron carriers? (2)

• NAD

• FAD

What is NAD derived from?

niacin

What are NAD and FAD reduced to? (2)

• NADH

• FADH

Where can an electron be added to NAD? (2)

• carbon

• nitrogen

What is the final electron acceptor?

oxygen

Why is oxygen a good final electron acceptor?

it is very electronegative

What are the stages of cellular respiration? (3)

• glycolysis

• pyruvate oxidation and the citric acid cycle

• oxidative phosphorylation

Where does glycolysis occur?

in the cytosol

What does glycolysis yield? (3)

• 2 pyruvates

• 2 ATP

• 2 NADH

Where does pyruvate oxidation and the citric acid cycle occur?

mitochondrial matrix

What does pyruvate oxidation yield? (4)

• 2 acetyl CoA

• 1 NADH

• 2H⁺

• 2 CO₂

What does the citric acid cycle yield? (5)

• oxaloaceate

• 2 CO₂

• 1 ATP

• 2 NADH

• 1 FADH

Where does oxidative phosphorylation occur?

mitochondrial matrix across the inner membrane

Oxidative Phosphorylation

transfer system that delivers electrons from NADH and FADH2 to oxygen and energy from electrons used to make ATP

What does oxidative phosphorylation yield?

34 ATP

Glycolysis

glucose and other molecules are partially oxidized and broken into smaller molecules

How many reactions occur in glycolysis?

10

What are the stages of glycolysis? (2)

• energy requiring

• energy releasing

What happens in the energy requiring steps of glycolysis? (2)

• 1 glucose → 2 glyceraldehyde-3-phosphate (G3P) molecules

• 2 ATP are hydrolyzed

What happens in the energy releasing steps of glycolysis? (3)

• 2 G3P → 2 pyruvate molecules

• 4 ATP are generated by substrate level phosphorylation

• 2 NAD+ are reduced to 2 NADH

What happens in Step 3 of glycolysis? (3)

• fructose-6-phosphate phosphorylated by phosphofructokinase to fructose-1,6-bisphosphate

• hydrolyzes ATP to provide Pi for kinase reaction

• directly burning energy to drive this reaction

Which steps in glycolysis lead to the release of energy? (3)

• Step 6

• Step 7

• Step 10

What happens in Step 10 of glycolysis? (3)

• phosphoenolpyruvate dephosphorylated by pyruvate kinase to pyruvate

• substrate level phosphorylation

• phosphorous on substrate is transferred to ADP to form ATP

What steps does substrate level phosphorylation occur? (2)

• Step 7

• Step 10

What are the major enzymes in glycolysis? (3)

• dehydrogenases

• isomerases

• kinase

Dehydrogenase (2)

• enzymes in cellular respiration that transfer electrons in redox reactions

• done by transferring hydrogen

Isomerases (2)

• enzymes that convert molecules to different isomers

• converts mainly structural isomers

Kinases

enzymes that phosphorylate substrates

How is glycolysis regulated?

ATP and AMP regulate phosphofructokinase allosterically

How is ATP involved in the regulation of glycolysis?

ATP negatively regulates phosphofructokinase if it is in abundance

How is AMP involved in the regulation of glycolysis? (2)

• AMP positively regulates phosphofructokinase if it is in abundance

• this increases the production of ATP

What does it mean if AMP is in high abundance?

ATP is low

What is a good example of substrate level phosphorylation? (2)

• the pyruvate kinase reaction

• the production of ATP in the citric acid cycle

What are the structural features of the mitochondria? (3)

• outer membrane

• inner membrane

• mitochondrial matrix

Double Membrane of Mitochondria (2)

• outer membrane

• inner membrane

Mitochondria (2)

• contain their own DNA and protein making machinery that make proteins important for cellular respiration

• use nuclear-gene derived products for mitochondria function

Why do mitochondria have their own DNA?

they come from prokaryotes

Where is most of the machinery in mitochondria made?

in the nucleus so those proteins have to be transported to the mitochondria

What happens to the mitochondrial proteins as a result of 2 genomes being involved?

they become complex quaternary structures

Which cellular respiration steps occur in the mitochondria? (2)

• pyruvate oxidation/citric acid cycle

• oxidative phosphorylation

What generally happens in pyruvate oxidation and the citric acid cycle? (5)

• 1 pyruvate is oxidized for every glucose to an acetyl group

• acetyl group is attached to CoA

• CoA bound to acetyl group goes through citric acid cycle by being bound to oxaloacetate

• carbons equivalent to the 2 made in a pyruvate molecule are lost as CO₂

• molecule of oxaloacetate remains at the end of the cycle to go through it again

What are the specific steps of pyruvate oxidation? (4)

• pyruvate is transported across the mitochondrial membrane by pyruvate transporter

• pyruvate will be oxidized to form an acetyl group (2C), which is transferred to CoA

• Carbon is lost as CO₂

• NAD is reduced to NADH

What is the mechanism used for the pyruvate transporter? (2)

• symporter that uses a hydrogen gradient

• secondary active transport

What is CoA made from? (2)

• vitamin B5

• cysteine

What is pyruvate oxidation performed by?

multienzyme complex

What is the chemical equation for pyruvate oxidation?

2 pyruvate + 2CoA + 2NAD+ = 2 acetyl CoA + NADH + 2H⁺ + 2CO₂

What happens in the first step of the citric acid cycle? (2)

• oxaloacetate is joined with acetyl-CoA to form citric acid by citrate synthase

• results in the release of CoA from the complex

What molecules regulate the first step of the citric acid cycle? (3)

• citrate (negatively)

• ATP (negatively)

• NADH (negatively)

How could citrate be negatively regulating the first step of the citric acid cycle?

allosterically

What are some of the key features of the cyclic nature of the cyclic acid cycle? (4)

• acetyl CoA is the input substrate

• 8 reactions in a cycle, so it is not linear

• in one cycle, the 2C acetyl unit that is input ends up in oxaloacetate

• 2 CO₂ in oxaloacetate are released

When in the citric acid cycle is there a removal of CO₂? (2)

• Step 3

• Step 4

Oxidative Phosphorylation (2)

• the electron transport chain (ETC) plus chemiosmosis by ATP synthase

• biggest payoff for ATP produced

Chemiosmosis

production of H⁺ gradient that provides energy for ATP production

ATP Synthase

composed of multiple proteins encoded by mitochondrial and nuclear genomes

What delivers electrons to oxygen in oxidative phosphorylation?

a series of electron carriers with increasing affinity for electrons

What happens to electrons as they pass through the system in oxidative phosphorylation?

H⁺ ions are pumped out of the matrix into the intermembrane space

What happens as a result of generating an H⁺ gradient in oxidative phosphorylation?

H⁺ gradient provides energy to ATP synthase to phosphorylate ADP to ATP

What happens in the electron transport chain? (3)

• electron shuttle molecules pass high energy electrons to protein complexes in the ETC

• as electrons pass down the series of redox reactions, energy is siphoned off in small packets to drive H⁺ transport against the gradient

• electrons finally end up with oxygen

What are the electron carriers in oxidative phosphorylation? (2)

• NADH

• FADH

What are the proton pumps in oxidative phosphorylation? (3)

• Complex I

• Complex III

• Complex IV

How is NADH delivered in oxidative phosphorylation?

through Complex I

How is FADH delivered in oxidative phosphorylation?

through Complex II

What happens when the electrons combine with oxygen and H⁺?

they make water

What is the equation for cellular respiration?

C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O + ~32 ATP

How efficient is cellular respiration?

30%

What does the efficiency of cellular respiration demonstrate?

the inefficiency of living systems

How can glycerol enter cellular respiration?

it can enter glycolysis as G3P

How can fatty acids enter cellular respiration?

it can enter the citric acid cycle as citrate

What happens when different macromolecules are entered into cellular respiration?

differing amounts of NADH, FADH, and ATP will be produced depending on where they are input into the cycle

What can cellular respiration be referred to?

central carbon metabolism (CCM)

What is required to perform oxidative phosphorylation?

oxygen

Fermentation (2)

• substrate level ATP synthesis occurs in glycolysis

• NADH is recycled to go back into the system the, transfers electrons to electron acceptor molecule

What happens in lactate fermentation? (2)

• glycolysis produces 2 ATP and 2 pyruvate

• pyruvate is converted to lactic acid

Why is lactate fermentation wasteful?

it barely produces ATP

Light-Dependent Reactions (2)

• energy of the sun is converted to chemical energy in the form of NADPH and ATP

• uses chemical energy

Light-Independent Reactions

energy from light-dependent reactions is used to convert inorganic CO₂ into organic C-containing molecules (carbon fixation)

Where are H⁺ and e^- derived? (2)

• water

• oxygen is released as a byproduct

How can C-containing molecules fixed by photosynthesis be used?

by animals and plants cellular respiration

What do plants do with glucose?

they use cellular respiration to break it down

Why do plants use amylose as a storage molecule?

ATP is not the best storage molecule

Chloroplast (4)

• metabolic organelle where photosynthesis occurs

• originally a prokaryote that coevolved to become a symbiote

• contain own DNA and protein making machinery

• use nuclear-gene derived product for function

What are the components of chloroplasts? (3)

• double membrane

• stroma

• thylakoids

Double Membrane of Chloroplast (2)

• outer and inner membrane

• between is the intermembrane space

Stroma (2)

• internal space

• where light independent reaction takes place

Thylakoids (3)

• membrane bound structures inside the stroma

• elaborated in structure to increase in surface area

• where light dependent reaction takes place

What is light energy absorbed by in photosynthesis? (2)

• chlorophylls

• carotenoids