General Biology unit 3

All cells have

1. ​Proteins = perform most of the cell’s functions

2. ​Nucleic acids = store, transmit, and process information

3. ​Carbohydrates = provide chemical energy, carbon, support, and identity

4. ​Plasma membrane = serves as a selectively permeable membrane barrier

What are the two fundamental types of cells based on morphology?

• Eukaryotes: Have a membrane-bound nucleus

• Prokaryotes: Do not have a membrane-bound nucleus

What are the three domains organisms are divided into?

1. Bacteria = prokaryotic

2. Archaea = prokaryotic

3. Eukarya = eukaryotic

Important structures and features of prokaryotic cells

• Have at least one chromosome (genetic material)

• Contain many ribosomes that make proteins

• Have phospholipids in their cell membrane

  • Bacteria: fatty acids attached to glycerol

  • Archaea: branched isoprenoid chains attached to glycerol

• Cytoplasm: the material inside the cell membrane that holds all the cell’s contents

chromosome in a prokaryotic cell

• Biggest structure inside a prokaryotic cell

• Usually one circular chromosome in bacteria and archaea

• Made of DNA + proteins

  • DNA holds the cell’s information

  • Proteins support the DNA’s structure

• Prokaryotes can also have plasmids: small circular DNA molecules that are separate from the main chromosome

What are ribosomes in prokaryotic cells and what do they do?

• Tiny “machines” inside the cell that make proteins

• Have large and small subunits

• Made of RNA and proteins

• Bacteria and archaea ribosomes are similar in size and function, but their RNA and protein components are slightly different

Cytoskeleton in bacteria and archaea

• Long, thin protein filaments in the cytoplasm

• Gives the cell structure and support

• Maintains cell shape

• Helps with cell division

Internal photosynthetic membranes in prokaryotes

• Found in some prokaryotes that do photosynthesis

• Convert sunlight into chemical energy

• Made of multiple membranes inside the cell, formed by infoldings of the plasma membrane

• Contain enzymes and pigments needed for photosynthesis

Organelles

• Internal compartments found in some bacterias

• Small structures inside the cell that perform special tasks

• Can store calcium ions

• Can hold magnetite crystals to act like a compass

• Can concentrate enzymes for making organic compounds

Cell wall

• Acts like a protective “exoskeleton”

• Made of a tough, fibrous layer surrounding the plasma membrane

• Maintains cell shape and rigidity

• In bacteria, main component is peptidoglycan

• Some bacteria also have an outer membrane made of glycolipids

Flagella and fimbriae in prokaryotes

• Structures that grow from the plasma membrane and interact with the environment

• Flagella: long filaments that rotate to move the cell

• Fimbriae: short, needlelike projections that help the cell attach to surfaces or other cells

Eukaryotes: size and types

• Include protists, fungi, plants, and animals

• Can be unicellular or multicellular

• Size: 5 – 100 µm in diameter

• Much larger than prokaryotic cells, which are 1 – 10 µm

• Range from microscopic algae to 100-meter-tall redwood trees

Organelles in eukaryotic cells

• Act like little compartments inside the cell

• Keep the watery part of the cell (cytosol) from being too crowded

• Help the cell work better by:

  1. Separating reactions that shouldn’t happen together

  2. Making reactions faster and more efficient

Nucleus in eukaryotic cells

• Big, organized compartment with a membrane

• Surrounded by a double membrane called the nuclear envelope with pores

• Inner surface attached to nuclear lamina (a protein “sheet” for support)

• Contains the nucleolus, where ribosomal RNA is made and ribosome subunits are assembled

Ribosomes

• Tiny machines that make proteins

• No membrane, so not true organelles

• Free in cytosol: make proteins that stay in the cytosol or go to other organelles (like the nucleus)

• Attached to ER: make proteins that will be sent out of the cell or to specific places

Endoplasmic reticulum (ER)

• Membrane-covered “factory” inside the cell

• Connected to the nuclear envelope

• Two types:

  1. Rough ER: has ribosomes; helps make proteins

  2. Smooth ER: no ribosomes; helps make lipids and other functions

Rough endoplasmic reticulum (RER)

• Covered with ribosomes (look like dark bumps)

• Makes proteins that will:

  1. Go to another organelle

  2. Become part of the plasma membrane

  3. Be secreted outside the cell

Protein processing in rough endoplasmic reticulum

• Proteins move into the lumen (inside of the sac-like RER)

• In the lumen, proteins are folded and processed

• Proteins made on RER can:

  1. Carry messages to other cells

  2. Act as membrane transporters or pumps

  3. Help speed up chemical reactions

Smooth endoplasmic reticulum (SER)

• Has no ribosomes

• Contains enzymes that:

  1. Make lipids needed by the cell

  2. Break down lipids and glycogen

  3. Detoxify waste, drugs, and harmful chemicals so they can be excreted

• Stores calcium ions (like in the sarcoplasmic reticulum)

Golgi apparatus

• modifies, packages, and ships proteins and lipids

• Proteins from the rough ER usually pass through the Golgi apparatus

• Made of stacked, flat membrane sacs called cisternae

• Has two sides:

  1. Cis surface – near the nucleus

  2. Trans surface – faces the plasma membrane

Function of Golgi apparatus

• Processes, sorts, and ships proteins made in the rough ER

• Cis side receives proteins from the rough ER

• Trans side sends proteins to other organelles or the cell surface

• Vesicles (small membrane bubbles) carry materials to and from the Golgi

Lysosomes

• Recycling centers found only in animal cells

• Contain about 40 different enzymes

• Enzymes break down waste, cellular debris, macromolecules, and foreign invaders

• Digestive enzymes are called acid hydrolases and work best at pH 5.0

• Proton pumps in the membrane keep the inside acidic

Endomembrane system

• Made up of the ER, Golgi apparatus, and lysosomes

• Produces, processes, and transports proteins, carbohydrates, and lipids

• Example: acid hydrolases

  1. Made in the ER

  2. Processed in the Golgi apparatus

  3. Shipped to lysosomes

Vacuole

• Large organelle found in plants, fungi, and some other eukaryotes

• Functions:

  1. Digest and recycle macromolecules

  2. Store water and ions

  3. In seeds, store proteins

  4. In petals or fruits, store pigments

  5. Can hold harmful compounds to protect the plant from being eaten

Peroxisomes

• Small round structures in all eukaryotic cells

• Made when vesicles from the ER are filled with special enzymes

• Help with chemical reactions that involve oxidation

• In plants, some peroxisomes (glyoxysomes) turn fats into energy

• Can make hydrogen peroxide, which is broken down safely by catalase

Mitochondria

• Supply ATP (energy) to the cell

• Have two membranes:

  1. Outer membrane – covers the organelle

  2. Inner membrane – folded into sac-like cristae

• Mitochondrial matrix – fluid inside the inner membrane

Mitochondria structure and DNA

• Mitochondria can fuse together or split apart

• Can form long, branched networks or exist as individual organelles

• Have their own mitochondrial DNA (mtDNA)

• Can grow and divide independently from the cell

• Make their own ribosomes

Chloroplasts

• Found in most plant and algal cells, site of photosynthesis

• Have three membranes

• Innermost membrane has thylakoids (flat sacs)

• Thylakoids are stacked into grana

• The fluid around thylakoids is the stroma, where enzymes use energy to make sugar

Chloroplast DNA

• Chloroplasts have their own DNA and make their own ribosomes

• Can grow and divide independently from the cell

Endosymbiosis theory

• Mitochondria and chloroplasts were once free-living bacteria

• Ancestor eukaryotic cells engulfed them but didn’t destroy them

• A mutually beneficial relationship developed

Cytoskeleton

• Network of protein fibers throughout the cell

• Gives the cell shape and support

• Moves materials around inside the cell

• Keeps organelles and other structures organized

Cell walls and extracellular matrix

• Fungi, algae, and plants have a stiff cell wall outside the plasma membrane

• Cell wall provides protection and support

• Animal cells do not have a cell wall

• Instead, they have an extracellular matrix (ECM) made of proteins and sugars that supports the cell

How does a cell’s shape and organelles relate to its job?

• The shape, size, and number of organelles match the cell’s job

• Fat cells are round and store lipids

• Cardiac muscle cells are long and tapered to help contract

• Different cells have different organelles depending on what they do

Differential centrifugation and fluorescence tags

• Method scientists use to separate parts of a cell and study them

• Cells use millions of ATP molecules every second for energy

• Enzymes speed up millions of reactions every second

• Membrane molecules can move across their cell or organelle in less than a minute

• Trillions of mitochondria in the body are replaced about every 10 days

Nucleus function

• Control center of eukaryotic cells

• Contains DNA with genetic information

• DNA is used to make RNA messages

• Nucleolus makes ribosomes by combining rRNA and proteins

• mRNA carries instructions from the nucleus to make proteins

Nuclear envelope

• Surrounds and separates the nucleus from the rest of the cell

• Has openings called nuclear pores that connect the nucleus to the cytosol

• Made of about 30 different proteins

• Lets important materials into the nucleus, like:

  • molecules used to build DNA and RNA

  • proteins needed for DNA replication, transcription, and ribosome production

• Very active transport: hundreds of molecules move through thousands of pores every second

Nuclear import (NLS and nuclear pores)

• Entry into the nucleus is selective

• Nuclear pores act like gates controlling what passes through

• Proteins need a nuclear localization signal (NLS) to enter

• NLS acts like a “zip code” that directs proteins to the nucleus

• Allows proteins to pass through nuclear pores into the nucleus

How are proteins targeted to the correct location in the cell?

• Most proteins are made in the cytosol and then transported

• Each protein has a specific “zip code” to reach the right place

• Special systems deliver proteins to the correct organelle

• Example: acid hydrolases are sent to lysosomes

Secretory pathway

• Pathway that moves proteins out of the cell

• Starts in the rough ER

• Moves to the Golgi apparatus

• Ends when the product leaves the cell

• Shows that the rough ER and Golgi work together as part of the endomembrane system

Signal hypothesis

• Proteins going to the endomembrane system have a “zip code”

• This directs them to the rough ER

• The zip code is a short ER signal sequence (~20 amino acids)

Protein processing in RER

• Proteins in the RER lumen are folded into their 3D shape

• Enzymes add carbohydrate groups in a process called glycosylation

• The protein is labeled and sent to the Golgi

Protein transport in vesicles

• Proteins travel in small membrane-bound vesicles

• Vesicles bud from the ER and move to the cis face of the Golgi

• Shown by pulse–chase and centrifugation experiments

How does the Golgi apparatus modify and move proteins?

• New cisternae form at the cis face

• Old cisternae break off from the trans face

• Each cisterna has different enzymes

• Proteins enter at cis face and are modified as they move through the Golgi

How are proteins directed to lysosomes from the Golgi apparatus?

• Proteins get a molecular tag in the Golgi

• Lysosome-bound proteins get mannose-6-phosphate

• Receptor proteins in the trans-Golgi recognize the tag

• This directs the protein to the lysosome

How do transport vesicles direct proteins to the correct destination?

• Proteins are packed into special vesicles called cargo complexes

• Each vesicle has a tag that shows where it should go

• Vesicles going to the plasma membrane release their proteins outside the cell (exocytosis)

How do lysosomes recycle materials in the cell?

• Cargo transport helps recycle proteins and other molecules

• Large molecules are broken down in lysosomes into smaller parts the cell can use

• There are three pathways lysosomes use to recycle materials

What is the cytoskeleton and what does it do?

• Dense network of fibers throughout the cell

• Provides structural support and helps maintain cell shape

• Not rigid; fibers can move and change

• Can alter the cell’s shape, move cell contents, and even move the whole cell

What are actin filaments and what do they do?

• Smallest parts of the cytoskeleton

• Made of actin protein subunits

• One of the most abundant proteins in animal cells (5–10% of total protein)

• Actin subunits join together through noncovalent bonds

• Usually located near the plasma membrane

What are intermediate filaments and what do they do?

• Made of different types of proteins, including keratins

• Keratins (about 20 types) are found in hair and nails

• Nuclear lamins are intermediate filaments that form the nuclear lamina

• Nuclear lamina shapes and stabilizes the nucleus

• Anchors chromosomes

• Nuclear envelope is broken down and rebuilt during cell division

What are microtubules and what do they do?

• Largest parts of the cytoskeleton, made of hollow tubes

• Built from α-tubulin and β-tubulin dimers

• Tubulin dimers join head-to-tail using noncovalent bonds

• Grow from the microtubule-organizing center (MTOC) near the nucleus

• Help separate chromosomes during mitosis and meiosis

• Dynamic: + ends grow faster than – end

How do vesicles move materials inside the cell?

• Vesicles carry materials to different parts of the cell

• Move along filament “tracks” in the cytoskeleton

• Microtubules guide vesicles, such as moving proteins from the RER to the Golgi apparatus

How do prokaryotic flagella differ from eukaryotic flagella?

• Flagella are long, hairlike structures that move cells

• Prokaryotic flagella: single helical rods made of proteins (flagellin in bacteria)

• Move by rotating like a propeller

• Eukaryotic flagella move by whipping back and forth

• Prokaryotic flagella are not covered by the plasma membrane, unlike eukaryotic flagella

How do eukaryotic flagella work?

• Longer than cilia, both are hairlike projections on some eukaryotic cells

• Made of microtubules in a 9+2 pattern called the axoneme

• Dynein motor proteins use ATP to create bending

• Movement of dynein arms causes the flagella to swim or move the cell

How do energy and enzymes support cellular activity?

• Cellular activities need energy and enzymes to happen

• Activities change based on signals from the cell or environment

• Enzymes control which reactions occur and when

• Help the cell get and use energy

• Metabolic pathways are ordered series of reactions that build or break down molecules

Two types of energy

• Kinetic energy: energy of motion

  • Example: thermal energy = energy from moving molecules

• Potential energy: stored energy in position or structure

  • Example: chemical energy = energy stored in chemical bonds

• Energy can be converted from one type to another

What determines the potential energy in a covalent bond?

• Depends on the position of shared electrons relative to the nuclei

• Longer, weaker bonds with evenly shared electrons have high potential energy

• Shorter, stronger bonds with unevenly shared electrons have low potential energy

How is energy transformed during chemical reactions?

• Products often have shorter, stronger bonds than reactants

• Potential energy in bonds decreases

• The lost energy is transformed into kinetic energy, like heat or light

first law of thermodynamics

• Energy is conserved

• Energy cannot be created or destroyed

• Energy can only be transferred and transformed

What is Enthalpy (H)

• Total energy of a molecule

• Includes potential energy in its bonds

• Also includes the effect of the molecule’s kinetic energy on surrounding pressure and volume

difference between exothermic and endothermic reactions

• Changes in enthalpy (ΔH) depend on differences in potential energy

• Exothermic reactions: release heat, ΔH is negative, products have less potential energy than reactants

• Endothermic reactions: absorb heat, ΔH is positive, products have more potential energy than reactants

What is entropy (S) and how does it relate to chemical reactions?

• Entropy (S) is the amount of disorder in a system

• If products are less ordered than reactants, entropy increases, ΔS is positive

• Second law of thermodynamics: total entropy of a system always increases

What is Gibbs free energy and how is it calculated?

• Gibbs free energy (G) shows if a reaction is spontaneous or needs energy input

• Change in G (ΔG) is calculated with: ΔG = ΔH – TΔS

  • ΔH = change in enthalpy

  • ΔS = change in entropy

  • T = temperature in Kelvin

When is a chemical reaction spontaneous or nonspontaneous?

• Reaction is spontaneous when ΔG < 0 → exergonic

• Reaction is nonspontaneous when ΔG > 0 → endergonic, needs energy input

• Reaction is at equilibrium when ΔG = 0

Why do some spontaneous reactions happen slowly, and what affects their speed?

• For reactions to happen, some bonds must break and others must form

• Molecules must collide in the right way so the electrons can interact

• Higher concentrations make more collisions, which speeds up the reaction

• Higher temperatures make molecules move more and collide more, which also speeds up the reaction

How do cells transfer energy to drive reactions?

• Energy from one reaction can power another reaction

• Happens in two ways:

  1. Transfer of electrons

  2. Transfer of a phosphate group

What are redox reactions and how do they work?

• Redox reactions involve electron transfer

• Oxidation = loss of electrons

• Reduction = gain of electrons

• Always happen together

• Oxidation releases energy (exergonic)

• Reduction uses energy (endergonic)

How are electrons gained or lost in redox reactions?

• Electrons can be gained or lost by:

  1. Changing the number of electrons in an atom’s valence shell

  2. Transferring electrons when new covalent bonds form

• This causes atoms to be oxidized or reduced

How do redox reactions affect electrons, protons, and energy?

• Electrons move from an electron donor to an electron acceptor

• Acceptors usually gain potential energy when reduced

• Electrons often travel with a proton (H+)

• Reduction usually adds protons

• Oxidation usually removes protons

What are Flavin adenine dinucleotide (FAD) and Nicotinamide adenine dinucleotide ( NAD+) and how do they work?

• FAD accepts two electrons and two protons → forms FADH2 (electron carrier with reducing power)

• NAD+ accepts two electrons and one proton → forms NADH (electron carrier)

• Both can easily donate electrons to other molecules

What is ATP and why does it store energy?

• ATP is the main energy currency for cells

• Fuels most cellular activities

• Also used to make RNA

• Has a lot of potential energy

• Stores energy in the bonds between its three negatively charged phosphate groups

• Negative charges repel, creating high potential energy

How does ATP release energy during hydrolysis?

• ATP reacts with water in a hydrolysis reaction

• The bond between the outermost phosphate and the next phosphate is broken

• Produces ADP and releases energy (highly exergonic)

• About 7.3 kilocalories of energy per mole of ATP is released

• 1 kilocalorie can raise 1 kilogram of water by 1°C

How do cells use ATP to power reactions?

• Cells don’t waste ATP energy as heat

• They use it for cell activities

• Phosphorylation adds a phosphate to a molecule

• This makes the molecule store more potential energy

• The molecule becomes an activated intermediate

• Phosphorylation helps drive reactions that need energy

What is activation energy and the transition state in a reaction?

• Activation energy is the energy needed to strain bonds so a reaction can happen

• Transition state is the middle point between breaking old bonds and forming new ones

• The transition state has high free energy

What do reactants need to do before a reaction can happen?

1. Reactants must collide in the right orientation

2. Must have enough kinetic energy to overcome the activation energy and reach the transition state

What do enzymes do in chemical reactions?

• Enzymes are catalysts that bring reactants together in the right orientation

• Make reactions more likely to happen

• Usually work for one specific type of reaction

• Reactants that bind to an enzyme are called substrates

How do substrates interact with an enzyme?

• Substrates bind to the enzyme’s active site

• Active-site binding helps substrates collide in the right orientation

• Bonds break and form to make products

• Many enzymes change shape when substrates bind; this is called an induced fit

What are the 3 steps of enzyme catalysis?

• Initiation – Substrate binds to the active site in the correct position

• Transition State Facilitation – Enzyme lowers activation energy using interactions with the substrate

• Termination – Products are released from the enzyme

How does substrate concentration affect the speed of an enzyme-catalyzed reaction?

• Low substrate: Reaction speed increases quickly (linear increase)

• Medium substrate: Speed increases but starts to slow down

• High substrate: Reaction rate levels off (plateaus)

• The reaction rate levels off because all the enzyme’s active sites are full, so it can’t work any faster

What are the non-enzyme molecules needed for enzyme function?

Enzymes sometimes need extra helper molecules to work properly:

• Cofactors – Inorganic ions (like Zn²⁺, Mg²⁺, Fe²⁺) that temporarily help enzymes

• Coenzymes – Organic molecules (like vitamins, NADH, FADH₂) that assist enzymes

• Prosthetic groups – Non-protein parts that are permanently attached to the enzyme

What affects enzyme structure and function?

• Enzyme shape is critical for function

• If shape changes, the enzyme may not work

• Factors that affect it:

  • Temperature

  • pH

  • Interactions with other molecules

  • Changes to its structure (primary structure)

How do temperature and pH affect enzymes?

• Temperature:

  • Changes folding and movement of enzyme and substrate

  • Changes kinetic energy

• pH:

  • Changes enzyme shape and reactivity

  • Changes charges on acidic/basic R-groups

• Both:

  • Affect enzyme shape and how well it works

How do regulatory molecules affect enzymes?

• Can change the enzyme’s structure

• Can change the enzyme’s ability to bind substrate

• Can either activate or deactivate the enzyme’s functio

How do covalent modifications regulate enzymes?

• Change the enzyme’s primary structure

• Can be reversible or irreversible

  • Irreversible: Often from cutting peptide bonds

  • Reversible (like phosphorylation):

    • Changes enzyme shape

    • Can activate or deactivate the enzyme

What is a metabolic pathway?

• A series of chemical reactions

• Each step has a different enzyme

• Helps build biological molecules

What is feedback inhibition?

• Happens when the final product of a pathway stops an enzyme in the pathway

• As product builds up, it “feeds back” to stop the reaction

• The starting substrate isn’t all used up

• Product can be stored or used in other reactions

What is the Horowitz model and how does it explain enzyme evolution?

• Enzymes evolved to make life’s building blocks

• If a substrate becomes scarce, new enzymes evolve to make more

• Retro-evolution: Backward steps repeated create multistep pathways

• Patchwork evolution: New enzymes get used in new pathways

• Bioremediation: Scientists can engineer new pathways to clean pollutants

What are catabolic and anabolic pathways?

• Catabolic pathways (exogenic):

  • Break down molecules

  • Release energy to make ATP

• Anabolic pathways (endogenic):

• Build larger molecules from smaller ones

• Use energy (ATP)

How do cells get and use energy?

• Cells need energy to function

• ATP is the main energy source for cells

• Energy comes from breaking down molecules like glucose

• This energy is used to turn ADP into ATP by adding a phosphate group

How do cells get and manage ATP?

• Cells only have enough ATP for 30 seconds to a few minutes of activity

• ATP is unstable, so cells are constantly making more

• Glucose sources:

  • Plants make it via photosynthesis

  • Other organisms get it from food

• Excess glucose is stored as glycogen or starch

How is energy from glucose used in cells?

• Burning glucose releases energy as heat and light

• In cells, glucose is broken down through controlled redox reactions

• Most of this energy is captured to make ATP

• This process is called cellular respiration

What are the four main steps of cellular respiration?

• Glycolysis: Glucose (6-carbons) → 2 pyruvate (3-carbons each)

• Pyruvate processing: Pyruvate → acetyl CoA

• Citric acid cycle: Acetyl CoA → CO₂

• Electron transport & oxidative phosphorylation: Electrons move through a chain → proton gradient → ATP production

What is cellular respiration and what do cells need for it?

• Cellular respiration: Reactions that use electrons from high-energy molecules to make ATP

• Cells need:

  • An energy source to make ATP

  • A carbon source to build macromolecules

Which macromolecules do cells use for ATP, and in what order?

• 1st: Carbohydrates

• 2nd: Fats

• 3rd: Proteins

• All three, carbohydrates, fats, and proteins, can provide substrates for cellular respiration

How are fats and proteins used in cellular respiration?

• Fats:

  • Broken into glycerol and fatty acids

  • Glycerol enters glycolysis

  • Fatty acids → acetyl CoA → citric acid cycle

• Proteins:

  • Broken into amino acids

  • Amino groups removed and excreted

  • Remaining carbon compounds → pyruvate, acetyl CoA, or other intermediates

  • Used in glycolysis and the citric acid cycle

How do cellular respiration intermediates help make macromolecules?

• Glycolysis intermediates → used to make nucleotides, which are needed for DNA and RNA.

• Acetyl CoA → used to make fatty acids, which are used to build fats and phospholipids.

• Citric acid cycle molecules → used to make many amino acids.

• Pyruvate → can be turned into glucose, which can then be stored as glycogen or starch.

Why are metabolic reactions organized into pathways?

• Metabolism has thousands of chemical reactions

• Organizing them into pathways helps regulate them

• Regulation keeps the cell’s environment stable under different conditions (homeostasis)

How was glycolysis discovered?

• Hans and Edward Buchner discovered it by accident in the 1890s

• They added sucrose to preserve yeast extracts

• Sucrose was unexpectedly broken down, producing alcohol

• Later research showed phosphorylation was involved

• Enzymes were found to be key to the process

What happens during glycolysis and what is the net yield?

• Glycolysis has 10 reactions in the cytosol

• Energy investment phase (reactions 1–5): Uses 2 ATP

• Energy payoff phase (reactions 6–10): Produces 2 ATP (by substrate-level phosphorylation) and NADH

• Net yield per glucose: 2 ATP, 2 NADH, 2 pyruvate

What are the key steps, enzymes, substrates, and products in glycolysis (Steps 1, 3, 7, 10)?

Step 1

• Enzyme: Hexokinase

• Substrate: Glucose

• Product: Glucose-6-phosphate (G6P)

Step 3

• Enzyme: Phosphofructokinase-1 (PFK-1)

• Substrate: Fructose-6-phosphate (F6P)

• Product: Fructose-1,6-bisphosphate (F1,6BP)

Step 7

• Enzyme: Phosphoglycerate kinase

• Substrate: 1,3-Bisphosphoglycerate (1,3BPG)

• Product: 3-Phosphoglycerate (3PG) + ATP (produced by substrate-level phosphorylation)

Step 10

• Enzyme: Pyruvate kinase

• Substrate: Phosphoenolpyruvate (PEP)

• Product: Pyruvate + ATP (produced by substrate-level phosphorylation)

How is glycolysis regulated by ATP?

• High ATP inhibits glycolysis at the third step (enzyme: phosphofructokinase)

• Phosphofructokinase has two ATP binding sites:

  • Active site: Low ATP → enzyme works → glycolysis continues

  • Regulatory site: High ATP → enzyme is inhibited → glycolysis slows down