Comprehensive Notes: Cellular Structure and Cellular Respiration

2.1 Cell Theory and Discovery

• Principles of the Cell Theory (Table 2-1):

  • The cell is the smallest structural and functional unit capable of carrying out life processes.

  • The functional activities of each cell depend on the specific structural properties of the cell.

  • Cells are the living building blocks of all multicellular organisms.

  • An organism's structure and function ultimately depend on the collective structural characteristics and functional capabilities of its cells.

  • All new cells and new life arise only from preexisting cells.

  • Because of this continuity of life, the cells of all organisms are fundamentally similar in structure and function.

• Overall idea: Cells are the basic units of life; organisms arise from cellular continuity; cellular characteristics determine function.

2.2 An Overview of Cell Structure

• Major cell divisions: plasma membrane, nucleus, cytoplasm.

• Important concepts introduced: roles of RNA, the human genome and proteome, epigenetics, and the lipidome.

• Cytoplasm definition: portion of the cell interior not occupied by the nucleus; includes organelles, cytoskeleton, and cytosol.

2.2 Plasma Membrane

• The plasma membrane bounds the cell; it is a thin membranous structure enclosing the cell.

• Composition: mostly lipid molecules with embedded proteins.

• Function: separates intracellular fluid (ICF) from extracellular fluid (ECF) and acts as a selective barrier.

• Proteins regulate movement of molecules between ICF and ECF, controlling entry of nutrients and export of products.

• It is not just a passive boundary; it actively regulates traffic into and out of the cell.

• See Chapter 3 for more detailed discussion of membrane structure and transport.

2.2 Nucleus

• The nucleus houses DNA organized into chromosomes.

• Each chromosome contains a different DNA molecule with a unique set of genes.

• Body cells contain 46 chromosomes (23 pairs).

• DNA’s two main functions:

  • Genetic blueprint during cell replication: ensures daughter cells are genetically identical; passes genetic characteristics to offspring in reproductive cells.

  • Directing protein synthesis: provides codes/instructions for synthesis of specific structural and enzymatic proteins.

• Proteins are the main structural components of cells; enzymes govern the rate of chemical reactions.

• Through gene expression, DNA indirectly governs most cell activities and serves as the cell’s control center.

2.3 Role of RNA in Protein Synthesis

• Three types of RNA involved in protein synthesis: mRNA, rRNA, tRNA.

• Process overview:

  • DNA’s genetic code for a protein is transcribed into mRNA.

  • mRNA exits the nucleus via nuclear pores and is read by ribosomes in the cytoplasm.

  • Ribosomes translate the mRNA code into an amino acid sequence for the protein.

  • rRNA is a core ribosome component.

  • tRNA delivers the appropriate amino acids to the ribosome during protein construction.

• Gene expression: the multi-step process by which information encoded in a gene directs protein synthesis.

2.3 Ribosomes

• Ribosomes are nonmembranous organelles where protein synthesis occurs.

• Rough endoplasmic reticulum (RER) membranes have ribosomes on their surface; they form the “rough” appearance.

• Free ribosomes are dispersed in the cytosol.

• Function: translate mRNA into amino acid chains; bring together mRNA, tRNA, amino acids; provide enzymes and energy for peptide bond formation.

• Each mRNA codes for a single protein.

2.3 Endoplasmic Reticulum and Segregated Synthesis

• ER is an elaborate, fluid-filled membranous system distributed throughout the cytosol.

• Primary functions: production of proteins and lipids.

• Rough ER (RER): synthesizes proteins for secretion and for membrane construction.

• Smooth ER (SER): packages newly synthesized proteins in transport vesicles.

• Misfolded proteins are targeted for destruction via the ubiquitin–proteasome pathway.

2.3 Ubiquitin-Proteasome Pathway

• Purpose: destroy misfolded or unwanted intracellular proteins.

• Key steps:
  1) Addition of ubiquitin to the target protein (tagging).
  2) The proteasome recognizes ubiquitin-tagged proteins and unfolds them; core proteolytic enzymes digest the protein into small peptides.
  3) Cytosolic enzymes degrade the released peptides to amino acids, which are reused for protein synthesis or energy.

• Notes: ubiquitin and proteasome components are recycled after degradation.

2.4 Golgi Complex and Exocytosis

• Golgi complex structure: stack of flattened, curved, membrane-enclosed sacs.

• COPI (coat protein I) mediates vesicular transport between Golgi sacs; sacs do not touch one another directly.

• In secretory cells, the Golgi packages proteins for export via exocytosis.

• Transport sequence (as summarized in the figure):

  • Rough ER → transport vesicles → Golgi complex

  • Vesicles fuse with Golgi membrane; contents are delivered into Golgi sacs

  • Proteins are modified, sorted, and directed to final destinations within vesicles

  • Secretory vesicles bud from the Golgi and await signals to fuse with the plasma membrane

  • Exocytosis: secretory products are released to the exterior; cytosol is not exposed to secreted products

  • Lysosomes also bud from the Golgi complex

• Key flow (simplified):

  • Rough ER → transport vesicles → Golgi → secretory vesicles → plasma membrane (exocytosis)

2.3–2.4 Detailed Process: Secretory Pathway Steps (Integrated)

• Stepwise outline (as per the summarized figure):
  1) The rough ER synthesizes proteins destined for secretion or for incorporation into the plasma membrane or other cell components.
  2) The smooth ER packages secretory products into transport vesicles.
  3) Vesicles fuse with the Golgi apparatus; contents enter the Golgi lumen.
  4) Proteins are modified while traveling through Golgi cisternae; sorting directs them to final destinations.
  5) Secretory vesicles containing finished proteins bud off the Golgi.
  6) Secretory vesicles await a signal; they fuse with the plasma membrane and secrete contents via exocytosis (contents released outside the cell).
  7) Lysosomes bud from the Golgi complex.

2.5 Lysosomes and Endocytosis

• Lysosomes: small, membrane-enclosed organelles containing hydrolytic enzymes.

• Functions:

  • Digest extracellular material brought into the cell by phagocytosis.

  • Remove worn-out or damaged organelles (autophagy-like processes).

• Endocytosis definitions and processes:

  • Internalization of extracellular material within the cell.

  • Types include pinocytosis (cell drinking), receptor-mediated endocytosis, and phagocytosis (cell eating).

2.6 Peroxisomes and Detoxification

• Peroxisomes: membranous organelles that detoxify a variety of wastes.

• Functions:

  • Produce and decompose hydrogen peroxide (H₂O₂).

  • Contain oxidative enzymes that remove hydrogen from various organic molecules, often using O₂.

2.7 Vaults as Cellular Trucks

• Vaults: nonmembranous organelles shaped like hollow octagonal barrels with a hollow interior.

• Proposed roles:

  • Transport within the cell, potentially from nucleus to cytoplasm.

  • May transport mRNA from the nucleus to ribosomal sites for protein synthesis.

  • May contribute to multidrug resistance observed in some cancer cells.

• Structural note: vaults can be closed or open depending on conformational state.

2.8 Cytosol: Cell Gel

• Cytosol definition: semiliquid portion of the cytoplasm surrounding organelles.

• Key activities in cytosol include:

  • Enzymatic regulation of intermediary metabolism.

  • Synthesis of ribosomal proteins.

  • Storage of fats, carbohydrates, and secretory vesicles.

2.9 Cytoskeleton: Cell “Bone and Muscle”

• The cytoskeleton forms an integrated network that supports cell shape and function.

• Major roles:

  • Maintains cell shape, rigidity, and spatial organization.

  • Serves as a lattice to organize enzymes and coordinate cellular activities.

  • Acts as a mechanical communication network and directs intracellular transport.

  • Regulates movements, intracellular trafficking, and structural integrity.

2.10 Cytoskeleton: Detailed Components

• Microtubules

  • Structure: long, slender, hollow tubes of tubulin.

  • Functions: maintain cell shape, coordinate movements, form mitotic spindle, serve as highways for vesicle transport, form cilia/flagella.

• Microfilaments

  • Structure: intertwined actin filaments; also contains myosin in muscle cells.

  • Functions: contractile systems; mechanical stiffeners for microvilli; enable amoeboid movement.

• Intermediate filaments (keratin as example)

  • Structure: irregular, threadlike proteins.

  • Functions: resist mechanical stress; stabilize cell structures, especially in mechanically stressed regions.

• Visuals: microtubules, microfilaments, and keratin overview diagrams show their subunits and assembly.

2.10 Microvilli and Motility Structures

• Microvilli: actin-supported projections on the plasma membrane increasing surface area for absorption.

• Cilia and flagella: motile protrusions used for movement.

  • Structure: 9+2 arrangement (nine doublets around a central pair) with dynein arms driving bending.

  • Base: basal body (centriole) anchors the axoneme.

  • Mechanism: dynein motor proteins slide adjacent microtubule doublets relative to each other, causing bending waves.

2.11 The Cytoplasm Components: Quick Reference (Table Summary)

• Membranous organelles:

  • Endoplasmic reticulum: extensive network; synthesizes proteins and lipids; rough ER for secretion/m membrane construction; smooth ER for packaging.

  • Golgi complex: modifies, packages, and distributes proteins; vesicular transport (COPI) between Golgi sacs; lysosomes bud from Golgi.

  • Lysosomes: digestive enzymes; degrade extracellular material and organelles.

  • Peroxisomes: detoxification and oxidative enzymes.

  • Mitochondria: powerhouse; ATP production; contains citric acid cycle enzymes, electron transport chain proteins, ATP synthase; inner membrane with cristae; matrix.

• Nonmembranous organelles:

  • Ribosomes: protein synthesis; some attached to rough ER, some free in cytosol.

  • Proteasomes: degrade tagged proteins.

  • Vaults: transport/storage roles (as above).

  • Centrioles: part of cytoskeleton organization, especially during mitosis.

• Inclusions and granules: glycogen granules, lipid droplets, etc.

• Cytosol: location of intermediary metabolism and various enzymes; site-specific activities.

2.12 Cell Cycle and Mitosis

• The Cell Cycle components (as summarized by Amoeba Sisters):

  • Interphase includes G₁ (growth), S (DNA replication), and G₂ (growth and preparation for mitosis).

  • Mitosis (M phase) includes prophase, prometaphase, metaphase, anaphase, and telophase.

  • Cytokinesis concludes cell division, producing two separate daughter cells.

• Checkpoints: key control points to ensure proper division and DNA integrity.

  • G₁ checkpoint: If DNA is damaged, apoptosis may occur; otherwise cell proceeds to S phase when growth signals and nutrients are present.

  • G₂ checkpoint: ensures DNA has replicated properly before mitosis.

  • M (spindle) checkpoint: ensures chromosomes are properly aligned and attached to spindle before proceeding with anaphase.

• Wealth of imagery and symbols emphasize control points and possible outcomes (Go-ahead or apoptosis).

2.13 Mitosis: Stages and Key Features

• Prophase: chromatin condenses into visible chromosomes; nucleolus disappears; centrosomes duplicate and move apart; spindle apparatus forms.

• Prometaphase: nuclear envelope fragments; microtubules interact with kinetochores on sister chromatids; spindle apparatus forms further; polar microtubules overlap.

• Metaphase: chromosomes align at the metaphase plate; kinetochores attached to opposite spindle poles.

• Anaphase: sister chromatids separate and move to opposite poles; each pole receives identical chromosomes.

• Telophase: chromosomes arrive at poles; nuclear envelopes re-form; nucleoli reappear; chromosomes de-condense.

• Visual cues: kinetochore microtubules, astral microtubules, spindle poles, and centrioles.

2.14 Cytokinesis

• Process following mitosis in which the cytoplasm divides to form two separate daughter cells.

• Key feature: cleavage furrow formation caused by a contractile actin ring (often shown with contractile ring proteins).

• Result: two genetically identical daughter cells, each with its own nucleus and cytoplasm.

2.15 Cellular Respiration: Overview and Key Equations

• Overall reaction (cellular respiration):

  • In words: glucose and oxygen are converted into carbon dioxide, water, and ATP.

  • Chemically: 6\,\mathrm{O2} + \mathrm{C6H{12}O6} \rightarrow 6\,\mathrm{CO2} + 6\,\mathrm{H2O} + \mathrm{ATP}

• Break down into main stages:

  • Glycolysis (cytosol): glucose to 2 pyruvate; net gain of 2\,\mathrm{ATP} and production of 2\,\mathrm{NADH}.\

  • Energy investment: 2 ATP consumed at the start.

  • Energy harvest: produces 2 ATP (net) and 2 NADH.

  • Pyruvate oxidation (to acetyl-CoA) and entry into the mitochondria: each pyruvate yields 1 NADH during conversion to acetyl-CoA; for 2 pyruvate, total 2\,\mathrm{NADH}.

  • Citric acid cycle (Krebs cycle) in the mitochondrial matrix: for each acetyl-CoA, one cycle yields multiple reduced electron carriers and ATP equivalents; for two turns per glucose, typical yields are: 4\,\mathrm{CO2}, 6\mathrm{NADH}, 2\mathrm{FADH2}, 2\mathrm{ATP(GTP)} (per glucose, this totals to 4 CO₂, 10 NADH, 2 FADH₂, and 2 ATP from substrate-level phosphorylation).

  • Oxidative phosphorylation (ETC and chemiosmosis) in the inner mitochondrial membrane:

  • Each NADH yields ~2.5 ATP; each FADH₂ yields ~1.5 ATP.

  • Total ATP from oxidative phosphorylation: (10\times 2.5) + (2\times 1.5) = 25 + 3 = 28 \text{ ATP}

  • Substrate-level ATP from glycolysis and the citric acid cycle adds to an overall typical yield of 32 ATP per glucose under many conditions.

• Total ATP yield: often summarized as \text{Total ATP} \approx 32 per glucose in eukaryotes, recognizing that exact yield can vary with shuttle systems and cellular conditions.

• Key components of the mitochondrion and pathway features:

  • Glycolysis occurs in the cytosol; products enter mitochondria as acetyl-CoA for the citric acid cycle.

  • Electron transport chain components include NADH and FADH₂ donors feeding protons across the inner mitochondrial membrane to generate a proton gradient used by ATP synthase.

  • Chemiosmosis drives ATP synthesis via ATP synthase.

2.16 Mitochondria: Form and Function (Recap)

• Mitochondria structure:

  • Outer membrane and inner membrane with cristae.

  • Intermembrane space and matrix as compartments.

  • Proteins of the electron transport system reside in the inner membrane; ATP synthase uses the proton gradient to produce ATP.

• Core processes:

  • Citric acid cycle (in matrix).

  • Oxidative phosphorylation (ETC + chemiosmosis in inner membrane).

2.17 Cytoskeleton, Movement, and Motor Proteins—Additional Notes

• Concluding thoughts on the interplay between cytoskeleton and organelle transport:

  • Microtubules guide secretory vesicles from ER to Golgi and beyond to the plasma membrane.

  • Microfilaments and motor proteins enable contractile movements and cytoplasmic streaming.

  • Cilia and flagella are driven by dynein arms that induce bending waves for movement.

2.18 Quick Concepts to Remember

• Core idea: structure and function of a cell arise from its organelles and their interactions; energy production and protein synthesis are central to cellular activity.

• Main organelles and their roles:

  • Plasma membrane: barrier and regulation of traffic.

  • Nucleus: genetic material and control center for gene expression.

  • ER and Golgi: protein/lipid synthesis, processing, and trafficking.

  • Lysosomes and peroxisomes: digestion and detoxification.

  • Mitochondria: ATP production via glycolysis, citric acid cycle, and oxidative phosphorylation.

  • Cytoskeleton: structural support and intracellular transport.

  • Vaults: potential transport roles and implications for drug resistance.

• Amoeba Sisters: Introduction to Cells and Cellular Respiration videos provide visual summaries of several concepts.

• YouTube links provided in the transcript (for further study):

  • https://youtu.be/8llzkri08kk

  • https://youtu.be/6ebDTPHOljU

  • https://www.youtube.com/watch?v=QVCjdNxJreE&t=191s

• Note: Videos are supplementary and not required for the written notes, but helpful for visualization.

Here are the answers to your questions based on the provided notes:

1. Principles of the Cell Theory

• The cell is the smallest structural and functional unit capable of carrying out life processes.

• The functional activities of each cell depend on the specific structural properties of the cell.

• Cells are the living building blocks of all multicellular organisms.

• An organism's structure and function ultimately depend on the collective structural characteristics and functional capabilities of its cells.

• All new cells and new life arise only from preexisting cells.

• Because of this continuity of life, the cells of all organisms are fundamentally similar in structure and function.

2. Major Subdivisions of the Cell

• Plasma Membrane: A thin membranous structure that bounds the cell, separating the intracellular fluid (ICF) from the extracellular fluid (ECF). It acts as a selective barrier, regulating the movement of molecules into and out of the cell.

• Nucleus: A central structure that houses the cell's DNA, organized into chromosomes. It serves as the cell's control center, directing protein synthesis and ensuring genetic continuity during cell replication.

• Cytoplasm: The portion of the cell interior not occupied by the nucleus. It includes:

  • Organelles: Distinct, highly organized, membrane-enclosed structures (e.g., ER, Golgi, lysosomes, mitochondria).

  • Cytoskeleton: An intricate protein network that maintains cell shape, provides mechanical support, and directs intracellular transport.

  • Cytosol: The semiliquid, gel-like portion of the cytoplasm where many metabolic activities occur and organelles are suspended.

3. What the Nucleus Contains

• The nucleus houses DNA (deoxyribonucleic acid), which is organized into chromosomes. Each chromosome contains a different DNA molecule with a unique set of genes. Human body cells typically contain 46 chromosomes (23 pairs).

4. Phases of the Cell Cycle and Mitosis

A. Cell Cycle Components:

• Interphase: The longest phase where the cell grows and prepares for division.

  • G₁ (Growth 1) phase: Cell grows and carries out normal metabolic functions. If DNA is damaged at the G₁ checkpoint, apoptosis may occur; otherwise, the cell proceeds to S phase.

  • S (Synthesis) phase: DNA replication occurs, resulting in two identical sister chromatids for each chromosome.

  • G₂ (Growth 2) phase: Cell continues to grow and synthesizes proteins necessary for mitosis. A G₂ checkpoint ensures DNA has replicated properly.

• Mitosis (M phase): The process of nuclear division.

  • Prophase: Chromatin condenses into visible chromosomes; the nucleolus disappears; centrosomes duplicate and move apart, forming the spindle apparatus.

  • Prometaphase: The nuclear envelope fragments; microtubules interact with kinetochores on sister chromatids; the spindle apparatus forms further.

  • Metaphase: Chromosomes align at the metaphase plate (the cell's equator); kinetochores are attached to opposite spindle poles. An M (spindle) checkpoint ensures proper alignment.

  • Anaphase: Sister chromatids separate and move to opposite poles of the cell, becoming individual chromosomes. Each pole receives an identical set of chromosomes.

  • Telophase: Chromosomes arrive at the poles and begin to de-condense; nuclear envelopes re-form around each set of chromosomes; nucleoli reappear.

• Cytokinesis: The final stage, following mitosis, where the cytoplasm divides, forming a cleavage furrow (caused by a contractile actin ring) and resulting in two separate, genetically identical daughter cells.

5. Roles of DNA, RNA, and Ribosomes in Protein Synthesis

• DNA (Deoxyribonucleic Acid): Houses the genetic code for protein synthesis within the nucleus. It serves as the genetic blueprint by providing the codes/instructions for the synthesis of specific structural and enzymatic proteins (gene expression). The information in DNA is transcribed into mRNA.

• RNA (Ribonucleic Acid): Three types of RNA are crucial:

  • mRNA (messenger RNA): Carries the genetic code (transcribed from DNA) from the nucleus to the cytoplasm, where it is read by ribosomes.

  • rRNA (ribosomal RNA): A core structural and catalytic component of ribosomes, essential for protein synthesis.

  • tRNA (transfer RNA): Delivers the appropriate amino acids to the ribosome based on the mRNA code, ensuring the correct sequence for protein construction.

• Ribosomes: Nonmembranous organelles found in the cytoplasm (free or attached to the rough ER). They are the sites where protein synthesis (translation) occurs. Ribosomes read the mRNA code, bring together mRNA, tRNA, and amino acids, and provide the enzymes and energy for peptide bond formation to create amino acid chains (proteins).

6. Table of Cellular Organelles and Their Functions

7. Ubiquitin-Proteasome Pathway

The ubiquitin-proteasome pathway is the cell's mechanism for destroying misfolded or unwanted intracellular proteins. The key steps are:

1. Tagging: Target proteins marked for destruction are tagged by the addition of small protein molecules called ubiquitin.

2. Recognition & Unfolding: A complex called the proteasome recognizes the ubiquitin-tagged proteins, unfolds them, and its core proteolytic enzymes digest the protein into small peptides.

3. Degradation & Recycling: Cytosolic enzymes further degrade the released peptides into individual amino acids, which can then be reused for new protein synthesis or energy production. Ubiquitin and proteasome components are recycled for future use.

8. Comparing and Contrasting Endocytosis and Exocytosis

Comparison (Similarities)

• Both are active transport mechanisms involving membrane-bound vesicles.

• Both are crucial for moving large molecules or substantial amounts of substance across the plasma membrane.

• Both involve fusion or budding of vesicles with the plasma membrane.

Contrast (Differences)

9. Components of the Cytoskeleton

• Microtubules:

  • Structure: Long, slender, hollow tubes composed of tubulin protein subunits.

  • Example Function: Maintain cell shape, coordinate intracellular movements (e.g., vesicle transport along "highways"), form the mitotic spindle during cell division, and are the structural basis for cilia and flagella.

• Microfilaments:

  • Structure: Solid, intertwined filaments primarily composed of actin protein; also contain myosin in muscle cells.

  • Example Function: Form contractile systems (e.g., muscle contraction), act as mechanical stiffeners for microvilli, and enable amoeboid movement.

• Intermediate Filaments:

  • Structure: Irregular, threadlike proteins with varying compositions depending on cell type (e.g., keratin).

  • Example Function: Resist mechanical stress, stabilize cell structures, particularly abundant in mechanically stressed regions such as the skin.

10. The 3 Steps of Cellular Respiration

(The notes describe the steps, but a diagram is not provided. Here is a description of the three main steps.)

1. Glycolysis:

   • Location: Cytosol.

   • Process: Glucose (a 6-carbon sugar) is broken down into two molecules of pyruvate (3-carbon molecules). This step involves an initial energy investment (2 ATP consumed) followed by an energy harvest.

2. Pyruvate Oxidation & Citric Acid Cycle (Krebs Cycle):

   • Location: Mitochondrial matrix.

   • Process - Pyruvate Oxidation: Each pyruvate molecule is converted into acetyl-CoA, releasing carbon dioxide ($ ext{CO}_2$) and producing NADH.

   • Process - Citric Acid Cycle: Acetyl-CoA enters the cycle, undergoing a series of reactions that fully oxidize the carbon atoms. This generates more carbon dioxide, as well as significant amounts of reduced electron carriers (NADH and FADH₂) and a small amount of ATP (or GTP).

3. Oxidative Phosphorylation (Electron Transport Chain & Chemiosmosis):

   • Location: Inner mitochondrial membrane.

   • Process - Electron Transport Chain (ETC): The NADH and FADH₂ generated in earlier steps donate high-energy electrons to a series of protein complexes embedded in the inner mitochondrial membrane. As electrons move down the chain, energy is released and used to pump protons ( ext{H}^+) from the mitochondrial matrix into the intermembrane space, creating a proton gradient.

   • Process - Chemiosmosis: Protons flow back into the matrix through a protein complex called ATP synthase. The energy released by this proton flow (proton-motive force) drives the synthesis of large amounts of ATP from ADP and inorganic phosphate.

11. Products of Glycolysis, Citric Acid Cycle, and Oxidative Phosphorylation

• Glycolysis (per glucose molecule):

  • Net: 2 ext{ ATP}

  • 2 ext{ NADH}

  • 2 ext{ Pyruvate}

• Citric Acid Cycle (per glucose molecule, i.e., two turns):

  • 4 ext{ CO}_2

  • 6 ext{ NADH}

  • 2 ext{ FADH}_2

  • 2 ext{ ATP (or GTP)} (via substrate-level phosphorylation)

• Oxidative Phosphorylation (per glucose molecule from 10 NADH and 2 FADH₂):

  • Approximately 28 ext{ ATP} (from electron transport and chemiosmosis)

  • 6 ext{ H}_2 ext{O} (formed at the end of the electron transport chain when oxygen accepts electrons)

12. Products of Glycolysis in Anaerobic Conditions

• The provided notes focus on aerobic cellular respiration and do not explicitly detail the products of glycolysis under anaerobic conditions. However, in the absence of oxygen, glycolysis still occurs, producing pyruvate and 2 ATP (net), and 2 NADH. To regenerate ext{NAD}^+ (which is required for glycolysis to continue), pyruvate is further metabolized through fermentation.

  • In animals (and some bacteria), pyruvate is converted to lactate.

  • In yeast (and some bacteria), pyruvate is converted to ethanol and carbon dioxide.