! BIOL 1020 Carbohydrates & Metabolic Pathways

LECTURES 13-17

What is the most common monosaccharide?

Glucose (C6H12O6)

In what 2 ways are monosaccharides classified by?

Location of the carbonyl group, number of carbons in the carbon skeleton

What type of reaction forms a disaccharide (union of 2 monosaccharides)?

Dehydration reaction

What is the bond created when a sugar is joined to another group?

Glycosidic linkage

What is the structure and function of a polysaccharide determined by what 2 things?

Its sugar monomers (monosaccharides) + positions of glycosidic linkages

Starch is a storage polysaccharide of plants, consisting entirely of _______ monomers

“glucose”

What is the storage polysaccharide in animals?

Glycogen

In what cells is glycogen typically found?

Liver and muscle cells

Cellulose is a polymer of glucose as well as starch, but their __________ linkages differ

“glycosidic”

The two ring forms of glucose in cellulose and starch are different. How do they differ?

Cellulose contains beta (β) glucose, starch contains alpha (α) glucose

Enzymes that hydrolyze/digest (α) linkages in starch cannot hydrolyze (β) linkages in ________

“cellulose”

What does cellulose in human food pass through the digestive tract as?

Insoluble fibre

What is chitin?

Structural polysaccharide found in arthropod exoskeletons

What can chitin additionally provide structural support for?

Fungal cell walls

Potential energy is contained in what type of bonds between atoms of complex organic molecules?

Covalent bonds

Is the breakdown of organic molecules exergonic or endergonic?

Exergonic (spontaneous, occurs without input of energy)

What 2 things does aerobic respiration consume?

Organic molecules + O₂

What’s the difference between aerobic and anaerobic respiration?

Anaerobic consumes compounds other than O₂

What is fermentation?

Partial degradation of sugars that occurs without O₂ (anaerobic process)

What are redox reactions (oxidation-reduction reactions)?

Chemical reactions that transfer electrons between reactants

What happens to a substance in oxidation?

Loses electrons or is oxidized

What happens to a substance in reduction?

Gains electrons or is reduced

Which is the reducing agent, the electron donor or acceptor?

Electron donor

Which is the oxidizing agent, the electron donor or acceptor?

Electron acceptor

Some redox reactions do not completely transfer electrons, but rather?

Change the degree of electron sharing in covalent bonds

Where are electrons from organic compounds usually first transferred to?

NAD⁺

As an electron acceptor, NAD⁺ functions as a/n _________ agent during cellular respiration

“oxidizing”

What is the reduced form of NAD⁺?

NADH

NADH contains stored energy that is later used to __________ ATP

“synthesize”

Where does NADH pass the high-energy electrons to?

The electron transport chain

What strong oxidizing agent pulls electrons down the electron transport chain (gas)?

O₂

In an uncontrolled reaction, how is all energy released?

All energy is released at once, as heat and light (explosion)

Does the electron transport chain release energy in a controlled or uncontrolled way?

Controlled

In what 3 stages does harvesting of energy from glucose occur?

Glycolysis, the citric acid/Krebs cycle (pyruvate oxidation), ETC (oxidative phosphorylation)

Glycolysis breaks down glucose into two molecules of ________

“pyruvate”

What does pyruvate oxidation and the citric acid cycle complete?

Breakdown of glucose

What does oxidative phosphorylation account for most of?

ATP synthesis

Why does oxidative phosphorylation generate most of the ATP?

Because it is powered by redox reactions

For each molecule of glucose broken down to CO₂ and water by respiration, the cell makes up to __ ATP

“32”

A small amount of ATP is formed during glycolysis and the citric acid cycle by what process?

Substrate-level phosphorylation (transfer of phosphate group from a bigger molecule to ADP, forming ATP; anaerobic)

The break down of glucose happens in a 10 step pathway, split into what 2 major phases in the cytosol?

Energy investment phase (1-5 steps), energy payoff (6-10 steps)

In the presence of O_2, pyruvate enters what organelle where oxidation continues?

Mitochondrion (in eukaryotic cells)

What does pyruvate oxidation link?

Glycolysis + the citric acid/Krebs cycle

Pyruvate oxidation involves what 3 reactions?

1. Carboxyl group released from pyruvate as CO₂

2. Remaining 2 carbon molecule is oxidized (to acetate), released electrons to NAD⁺ reduce it to NADH

3. Resulting acetyl group transferred to coenzyme A, forming Acetyl-CoA

Acetyl-CoA can now enter the citric acid/Krebs cycle!

Each acetyl group leads to one turn of the cycle, which generates how many of what 3 molecules?

1 ATP, 3 NADH, and 1 FADH₂

How many steps make up the Citric Acid Cycle/Krebs cycle?

8 steps (each catalyzed by a different enzyme)

2-C acetyl group from Acetyl-CoA enters the cycle by being combined with 4-C oxaloacetate to form ______?

“citrate” (6-C)

If the first step of the citric acid cycle forms citrate, what do the next 7 steps do?

The next seven steps decompose citrate back to oxaloacetate, making the process a cycle

What do NADH and FADH₂ produced during the cycle carry?

High-energy electrons → ETC

Where is most energy during glycolysis, pyruvate oxidation and the citric acid cycle extracted from organic molecules transferred to?

NADH and FADH₂

NADH and FADH₂ both donate electrons to where to power ATP synthesis?

ETC

By what process can NADH and FADH₂ donate electrons to the ETC?

Oxidative phosphorylation

Where is the ETC located?

In cristae (folds in inner membrane of mitochondrion)

Electron carriers alternate between reduced and oxidized states as they ______ and _______ electrons

“accept,” “donate”

In the ETC, where are electrons ultimately donated to?

O₂ (to form H₂O)

Electrons from NADH and FADH₂ are passed through a series of electron carriers, including ____________, ultimately to O₂

“cytochromes” (primary electron carrier in ETC)

T/F: The electron transport chain (ETC) generates ATP directly

False, it does not, only breaks up free-energy

Energy released during electron transfer through ETC is used to pump what ion from the mitochondrial matrix to the intermembrane space?

H⁺

When H⁺ is pumped from the ETC, it generates a ________

“gradient”

When H⁺ is pumped from the ETC, where does it flow?

Down concentration gradient → across the inner membrane → through ATP synthase

What does ATP synthase use the exergonic flow of H⁺ for?

To drive phosphorylation of ADP to form ATP

What is chemiosmosis?

The use of energy in a H⁺ gradient to drive cellular work

Energy stored in the H⁺ gradient across the inner mitochondrial membrane couples what? _{(“Couples” meaning energy from exergonic powering endergonic)}

Redox reactions of ETC → ATP synthesis

What is the proton-motive force?

Energy in H⁺ gradient, used to power ATP synthesis and other cellular processes

During cellular respiration, in what sequence does most energy flow in (start from glucose → end with ATP)?

Glucose → NADH → ETC → proton-motive force → ATP

Where is about 34% of energy in a glucose molecule transferred to (via cellular respiration)?

ATP, making about 30-32 ATP

Without O₂, what happens to the electron transport chain?

It will stop working/cease to operate

In the absence of O₂, what does glycolysis couple with to produce ATP?

Fermentation (anaerobic process)

What is anaerobic respiration?

A process that uses an ETC with a final electron acceptor other than O₂, (e.g. sulphate)

What does fermentation enable?

Enables glycolysis to continue making ATP by substrate-level phosphorylation

What does fermentation regenerate so that glycolysis can continue?

NAD⁺

What are 2 common types of fermentation?

Alcohol fermentation + lactic acid fermentation

What is alcohol fermentation?

Pyruvate is converted to ethanol in 2 steps;

1. Releasing CO₂

2. Regenerating NAD⁺ (to be used in glycolysis).

In lactic acid fermentation, pyruvate is reduced by NADH to yield NADH⁺, forming what as an end product?

Lactate (without release of CO₂, like alcohol fermentation)

When do human muscle cells use lactic acid fermentation?

To generate ATP when O₂ is scarce

NAD⁺ is always the oxidizing agent that _______ electrons

“accepts”

Fermentation, anaerobic and aerobic respiration all use what process to oxidize glucose and harvest chemical energy from food?

Glycolysis

Cellular respiration produces 32 ATP per glucose, whereas fermentation produces how many ATP per glucose?

2 ATP per glucose

What are obligate anaerobes?

Microorganisms that carry out fermentation or anaerobic respiration

What happens to obligate anaerobes in presence of O₂?

They cannot survive

What are facultative anaerobes?

Microorganisms that can survive with or without oxygen (aerobic or anaerobic), but prefer oxygen (aerobic)

In facultative anaerobes, what does pyruvate represent?

A fork leading to 2 alternative catabolic routes

The light reactions of photosynthesis convert solar energy to ATP and?

NADPH

The Calvin cycle takes chemical energy to do what?

To reduce CO₂ to sugar

Photosynthesis converts solar energy into what kind of energy?

Chemical energy

What type of fuels can supplement and potentially replace fossil fuels?

Biofuels

What are the 2 types of biofuels covered in BIOL 1020?

Bioethanol + biodiesel

Bioethanol consists of ethanol from glucose from?

Plant starch

Biodiesel uses what from unicellular algae?

Plant oils

In what membranes are photosynthetic enzymes arranged together in?

Thylakoid membranes

What part of a plant is the major location of photosynthesis?

Leaves

Chloroplasts are found mainly in what cells in leaves?

Mesophyll cells

Mesophyll cells contain roughly how many chloroplasts each?

30-40 chloroplasts

CO₂ enters/O₂ exits leaves through what structure?

Stomata

Chloroplasts are surrounded by two envelope membranes, enclosing a dense interior fluid called the?

Stroma

The interior thylakoid membranes form what?

Interconnected sacs

What pigment is in thylakoid membranes, that give leaves their green colour?

Chlorophyll

Thylakoids may be stacked in structures called?

Grana

What plant organelles split H₂O into its elements?

Chloroplasts

Photosynthesis is a redox process, in which ___ is oxidized, and ___ is reduced.

“H₂O" to O₂, “CO₂” to sugar (glucose)