how cells obtain energy - cell bio

metabolism

sum of all the chemical reactions in a cell

what does metabolism consist of

hundreds of chemical reactions

catabolism

breakdown of nutrients to release energy

anabolism

synthesis of molecules within cells

what do catabolic pathways produce

CO2, H2O, energy

what do pathways transform

substrates into products, via specific intermediates/metabolites

what do enzymes increase

ROR

how do enzymes work

have an active site in which substrate molecules fit

what do the amino acids in the active site of the enzyme protein do

attract the substrate, assist in chemical reactions that convert the substrate to the product, alters the substrate to make the reaction more favourable

What is the most common energy currency molecule in the cell?

ATP

What are the 3 structural components of ATP?

adenine, ribose, 3 phosphate groups

What type of bond joins the phosphate groups in ATP, and why does breaking it release energy?

Phosphoanhydride bonds, high energy bonds which when hydrolysed release free energy that the cell can use to do work

What is ATP hydrolysed into when it releases its energy?

ADP + Pi

What direction of energy transfer occurs when ADP + Pi → ATP?

energy input is required, energetically unfavourable reaction driven by energy from food/sunlight

What direction of energy transfer occurs when ATP → ADP + Pi?

energy is released, made available for cellular work and chemical synthesis

How does ATP drive an otherwise energetically unfavorable reaction (e.g. joining molecule A to molecule B)?

In an "activation step," ATP transfers a phosphate group to one of the reactants (e.g. B–OH → B–P), releasing ADP + Pi; this "activated" high-energy intermediate then undergoes a "condensation step" where it reacts with the other molecule (A) to form the final product (A–B), releasing the phosphate and H2O

In the amino acid activation example (glutamic acid → glutamine), what does ATP do in the "activation step"?

ATP phosphorylates the –OH group of glutamic acid, forming a high-energy phosphorylated intermediate + ADP + Pi

In the amino acid activation example, what happens in the "condensation step"?

Ammonia (NH3) reacts with the high-energy intermediate, displacing the phosphate group (+H2O) to form glutamine (the amide product)

Why do cells need a two-step "activation + condensation" strategy instead of just directly joining two molecules?

Directly joining two stable molecules is often energetically unfavorable; coupling the reaction to ATP hydrolysis (via a high-energy intermediate) makes the overall reaction favorable

What are the two general ways cells make ATP?

Direct ATP synthesis — substrate-level phosphorylation, and Indirect ATP synthesis — via electron carriers and oxidative phosphorylation

Define "substrate-level phosphorylation."

The direct transfer of a high-energy phosphate group from a phosphorylated substrate straight onto ADP, forming ATP — catalysed by an enzyme, no electron transport chain involved

In which two pathways does substrate-level phosphorylation (direct ATP synthesis) occur?

A few steps in glycolysis, and a step in the Krebs (citric acid) cycle

What is the most common electron carrier (coenzyme) used in indirect ATP synthesis?

NAD+

What happens to NAD+ when it accepts electrons and H+ from food breakdown?

It is reduced to NADH

What happens to NADH once it reaches the mitochondria?

oxidised back to NAD+, releasing its electrons and energy, which is used to synthesize ATP

In the "activated carrier molecule" analogy, what does the energetically favorable reaction (food molecule → oxidized food molecule) do?

provides the energy that reduces NAD+ to NADH

what does the energetically unfavorable reaction (molecule available in cell → molecule needed by cell) require?

Energy released when NADH is oxidised back to NAD+

Which process (catabolism or anabolism) reduces NAD+ to NADH, and which uses NADH's energy?

Catabolism reduces NAD+ → NADH, anabolism uses NADH's stored energy

What 3 macronutrient types can be broken down to make acetyl CoA?

glucose (glycolysis), fats (fatty acids), amino acids

What are the 3 stages of nutrient breakdown

1 - breakdown of large macromolecules to simple subunits, 2 - breakdown of simple subunits to acetyl CoA, 3 - complete oxidation of acetyl CoA to CO2 + H2O via the citric acid cycle and oxidative phosphorylation

Which stage of nutrient breakdown produces the LARGE majority of ATP?

stage 3

What are the 3 major stages of glucose breakdown, and where does each occur?

Glycolysis (cytosol) → Krebs/citric acid cycle (mitochondrial matrix) → Electron transport chain & oxidative phosphorylation (inner mitochondrial membrane)

Which of the 3 stages of glucose breakdown use direct (substrate-level) phosphorylation, and which uses indirect (oxidative) phosphorylation?

Glycolysis and the Krebs cycle use substrate-level (direct) phosphorylation; the electron transport chain/oxidative phosphorylation stage uses indirect phosphorylation via ATP synthase

Where in the cell does glycolysis occur?

cytosol

Does glycolysis require oxygen?

no

What is the overall input and output of glycolysis (per 1 glucose)?

Input: 1 glucose + 2 ATP invested. Output: 4 ATP produced (2 ATP net), 2 NADH, 2 pyruvate

What is the NET ATP yield of glycolysis per glucose molecule?

2 ATP (net) because 2 ATP are invested early on and 4 ATP are produced later

What happens to electrons removed during the "step-wise oxidation of sugars" in glycolysis?

They are used to reduce NAD+ to NADH

How is ATP produced directly during glycolysis?

Via substrate-level phosphorylation (direct transfer of a phosphate group from an intermediate to ADP)

What happens to the NADH produced in glycolysis?

It can move into the mitochondria to be used for indirect ATP synthesis (oxidative phosphorylation)

In "How Glycolysis Works," a 6-carbon sugar is split into what, and what molecules are generated per 3-carbon fragment?

Split into two 3-carbon sugar phosphates; each is converted to a 3-carbon pyruvate, generating NADH and ATP along the way

What enzyme complex converts pyruvate into acetyl CoA?

Pyruvate dehydrogenase enzyme complex

Where does the bridge reaction (pyruvate → acetyl CoA) occur?

In the mitochondrial matrix

What are the products from ONE pyruvate entering the bridge reaction?

1x Acetyl CoA + 1x NADH + 1x CO2

Since glycolysis produces 2 pyruvate per glucose, what are the TOTAL products of the bridge reaction per glucose?

2x Acetyl CoA + 2x NADH + 2x CO2

What 2 molecules combine to start the Krebs cycle, and what do they form?

Acetyl CoA (2 carbons) + oxaloacetate (4 carbons) combine to form citrate (6 carbons)

What happens to citrate as it moves around the Krebs cycle?

gradually oxidised

What are the total products of the Krebs cycle from ONE acetyl CoA (i.e., one "turn" of the cycle)?

3 NADH, 1 FADH2, 1 ATP (direct/substrate-level phosphorylation), 2 CO2

What happens to oxaloacetate at the end of one turn of the Krebs cycle?

It is reformed/regenerated, ready to combine with another acetyl CoA and start the cycle again

Approximately how much ATP does each NADH yield when it later passes through oxidative phosphorylation?

~2.5 ATP per NADH

Approximately how much ATP does each FADH2 yield when it later passes through oxidative phosphorylation?

~1.5 ATP per FADH2

Besides ATP production, what other important role do glycolysis and the Krebs cycle play?

provide precursor molecules for biosynthesis of important biological molecules i.e. nucleotides, amino acids

Is glycolysis a linear or cyclic pathway? What about the Krebs cycle?

Glycolysis = linear pathway; Krebs cycle = cyclic pathway

Where does oxidative phosphorylation take place in eukaryotic cells?

The mitochondrial inner membrane

What two molecules drive oxidative phosphorylation (indirect ATP synthesis)

NADH and FADH2

What are the 2 processes that together make up oxidative phosphorylation?

(1) "Oxidative" = the electron transport chain; (2) "Phosphorylation" = ATP synthesis (via ATP synthase)

When NADH is oxidised to NAD+ in the mitochondria, what happens to the released electrons?

They are passed along the electron transport chain — a series of membrane-bound protein complexes/enzymes that accept the electrons (getting reduced) and then pass them on

As electrons move through the electron transport chain, what happens to their energy?

They gradually lose energy, and this released energy is used to pump H+ ions across the inner mitochondrial membrane, from the matrix into the intermembrane space

What does pumping H+ into the intermembrane space create, and why does it matter?

It creates a steep H+ concentration gradient across the inner mitochondrial membrane — this gradient's energy is used to drive ATP synthesis

What happens to electrons at the very end of the electron transport chain?

They combine with O2 (and H+) to form H2O

What are ATP synthases, structurally and functionally?

Large multi-subunit proteins embedded in the inner mitochondrial membrane that act as energy-generating molecular motors

How does ATP synthase convert the H+ gradient into ATP?

It converts the energy from H+ flowing down its concentration gradient into mechanical energy (rotating stalks pushing against stationary head proteins), which is then converted into chemical bond energy — forming a bond between ADP and Pi to make ATP

Roughly how many ATP molecules can ATP synthase produce per second?

About 100 molecules of ATP per second

Roughly how many H+ ions need to move through ATP synthase to produce 1 ATP?

Approximately 4 H+

What are the 2 sets of proteins that make up ATP synthase, and what do they do?

Rotating stalks and stationary heads — the stalks rotate and push against the heads, causing a conformational change in the head subunits that drives ATP formation

Which stage of glucose breakdown uses direct substrate-level phosphorylation to make ATP in the cytosol?

glycolysis

Which stage of glucose breakdown uses direct substrate-level phosphorylation to make ATP in the mitochondrion?

The Krebs cycle

Which stage of glucose breakdown produces ATP via oxidative (indirect) phosphorylation?

The electron transport chain, using ATP synthase, in the inner mitochondrial membrane

What carries electrons from glycolysis into the mitochondrion for oxidative phosphorylation?

NADH

What carries electrons from the Krebs cycle to the electron transport chain?

NADH and FADH2

What happens chemically when ATP is "used" by the cell?

It is broken down (hydrolysed) to ADP + Pi, releasing energy

Name 3 types of cellular work powered by ATP hydrolysis

catalysis, muscle contraction, biosynthesis

What drives most of the body's resting energy expenditure?

Processes powered by ATP hydrolysis

Approximately how much ATP does the human body use/recycle each day?

Roughly its own body weight in ATP each day