CELS191 Lectures 1-7 Summary

Characteristics of Life

• Cellular organisation: arrangement of components inside a cell.

• Reproduction: producing offspring (sexual or asexual).

• Metabolism: chemical reactions to convert macromolecules into energy, building blocks, and waste.

• Homeostasis: maintaining a constant internal state.

• Heredity: passing genetic information to the next generation.

• Response to stimuli: sensing and responding to environmental changes.

• Growth and development: increases in size and maturity.

• Adaptation through evolution: becoming better suited to the environment over generations.

The Tree of Life

• A phylogenetic tree showing how ALL life is related.

• Constructed using DNA sequences.

• Groups life into three domains: Bacteria, Archaea, Eukarya.

Phylogenetic Trees

• Diagram showing species relationships.

• Branches represent time or differences between species.

• Nodes represent the last common ancestor.

• Closer species are more closely related.

The Tree of Life

• DNA sequences used to construct the tree.

• Three domains: Bacteria, Archaea, Eukarya (includes animals, plants, fungi, protists).

Biological Classifications

• Domains are the highest rank.

• Divided into kingdoms, then further to species.

• Examples: Lion (Panthera leo), Kumara (Ipomoea batatas), Tuberculosis Bacteria (Mycobacterium tuberculosis).

Eukaryotes vs Prokaryotes

• Eukaryotes:

  • Domain Eukarya.

  • Single or multi-celled.

  • Large cell size (10-100 µm).

  • Have organelles (nucleus, Golgi body, mitochondria).

  • Photosynthetic eukaryotes have chloroplasts.

• Prokaryotes:

  • Domains Archaea and Bacteria.

  • Single-celled.

  • Small cell size (1-5 µm).

  • Lack organelles.

Common Cell Structures

• All cells have a plasma membrane, cytosol, ribosomes, and chromosomes.

• Some cells have a cell wall (prokaryotic or eukaryotic).

Endosymbiont Theory

• Mitochondria and chloroplasts derived from free-living prokaryotic cells.

  • Mitochondria from proteobacteria (aerobic bacteria).

  • Chloroplasts from cyanobacteria (photosynthetic bacteria).

• Engulfed by larger host cells and not broken down.

Endosymbiont Theory: Continued

• Mutual benefit within the larger prokaryotic cell (symbiosis).

• Engulfed bacteria became specialized.

• Mitochondria and chloroplasts are semi-autonomous: have their own DNA, ribosomes, and can synthesize some proteins.

Endosymbiont Theory: Timeline

• Origin of life Bacteria, Archaea, and Eukarya emerge.

• Endosymbiosis leads to the origin of mitochondria and chloroplasts.

Tutorial 2

Learning Objectives for Tutorial 2

• Describe the structure of the plasma membrane and outline its importance to cell function.

• Describe the roles of carbohydrates, lipids, and proteins.

• Outline mechanisms by which substances cross the plasma membrane (passive transport, active transport, and co-transport).

• Outline the bulk transport processes of endocytosis (phagocytosis, pinocytosis, receptor-mediated endocytosis) and exocytosis (constitutive and regulated).

Biological Membranes:

• Supramolecular structures around cells (eukaryotic and prokaryotic).

• Semi-permeable: control movement of substances.

• Separate cell interior from external environment and surround organelles.

• Made from lipids, proteins, and carbohydrates.

Macromolecules: Lipids

• Not polymeric, heterogeneous, hydrophobic.

• Examples: steroids, phospholipids, triacylglycerols.

• Phospholipids and cholesterol are key structural components.

Macromolecules: Lipids - Phospholipids

• Major component of cell membranes.

• Hydrophilic phosphate head and hydrophobic fatty acid tails form a bilayer.

• Dynamic: can move about side-to-side.

Macromolecules: Lipids - Cholesterol

• Component of cell membranes in animal cells.

• Steroid with a four-ring structure.

• Moderates membrane fluidity.

Lipids: Membrane Fluidity

• Cell membranes are fluid (flexible).

• Important for permeability.

• Enables protein movement.

• Affected by:

  • Phospholipid fatty acid tail saturation (unsaturated tails = more fluid; saturated tails = less fluid).

  • Cholesterol content (limits packing at cold temperatures, prevents excess fluidity at high temperatures).

Macromolecules: Proteins

• Perform cell functions (workhorse).

• Diverse and abundant.

• Polymeric: monomer is an amino acid.

• 20 amino acids differ by their ‘R’ group (side chain).

Proteins in Membranes

• Proteins are a component of membranes, often with sugars attached (glycoproteins).

• Functions include: -Transport

  • Signal transduction
    -Enzyme activity
    -Cell-cell recognition
    -Intercellular joining
    -Attachment to extracellular matrix

Macromolecules: Carbohydrates

• Sugars and macromolecules of sugars.

• Building structures.

• Energy storage.

• Involved in recognition.

• Monosaccharides are the monomer form.

Carbohydrates in Membranes

• Attach to membrane proteins (glycoproteins) and lipids (glycolipids).

• Glycoproteins play a role in cell-cell recognition.

• Glycolipids stabilize the membrane and are involved in cell-cell recognition.

Biological Membranes Functions

• Moderate what can enter/exit a cell (or organelle).

• Facilitate membrane transport and selective permeability.

• Organelles:
  -Separate incompatible processes
  -Concentrate substances and form gradients
  -Act as sites for specific functions

Membrane Transport: Diffusion

• Some molecules move directly across the membrane (diffusion).

• Movement from high to low concentration (passive transport, no energy required).

• Lipids (steroid hormones)
  -Lipid soluble molecules
  -Lipid soluble gases

Membrane Transport: Facilitated Diffusion

• Molecules move across membranes down their concentration gradient, aided by proteins (passive transport).

• Channel proteins: corridors for specific molecules/ions (e.g., aquaporins for water).

• Carrier proteins: alternate shapes to move solutes (e.g., glucose transporter).

Membrane Transport: Active Transport

• Substances moved against concentration gradient.

• Requires energy (ATP) and carrier proteins.

• Accumulates substances or maintains low concentrations.
  Ex: The sodium-potassium pump that brings potassium in and pumps sodium out (both against concentration gradient) of cell.

Membrane Transport: Co-Transport

• Diffusion of one substance (A) is coupled to the transport of another (B) against its gradient (indirect active transport).

• Ex: H+/sucrose co-transporter (H+ diffuses down its gradient, pulling sucrose along).

Membrane Transport: Bulk Transport

• Large molecules moved via vesicles/vacuoles (active transport).
  -Forms: exocytosis (out) and endocytosis (in).

Bulk Transport: Exocytosis

• Cellular secretion of biological molecules.

• Vesicles fuse with the plasma membrane.
  Forms:
  -Constitutive exocytosis (constant release, e.g., extracellular matrix glycoproteins).
  -Regulated exocytosis (release upon signal, e.g., insulin).

Bulk Transport: Endocytosis

• Intake of biological molecules from outside the cell.

• Plasma membrane forms “fingers” that wrap around material.

  Forms: -
  -Phagocytosis (cellular eating)- uptake of large particles or organisms.
  -Pinocytosis (cellular drinking)- uptake of extracellular fluid.
  -Receptor-mediated endocytosis - acquisition of specific substances at low concentrations.

Tutorial 3

Learning Objectives

• Outline the origin of chloroplasts and mitochondria (endosymbiosis).

• Outline the process of energy supply in both plant and animal cells.

• Outline how cells capture light energy and transduce it to cellular energy in the two stages of photosynthesis.

• Outline the mechanism of ATP synthesis and the role of ATP in powering the cell.

• Describe the importance of cellular compartments in energy conversion.

Chloroplasts vs Mitochondria

• Both an organelle (not part of endomembrane system).

• Both in eukaryotic cells, not prokaryotic cells.

• Both have own DNA & ribosomes.

• Both originally derived from free-living prokaryotic cells (Endosymbiotic Theory).

  Chloroplasts

• 4 to 7 µm long

• 30 to 40 per cell

• Green

• Site of photosynthesis Mitochondria

Mitochondria

• 1 to 10 µm long

• 1 to 1000’s per cell

• “Powerhouse of the cell”

• Site of cellular respiration

Chloroplasts vs Mitochondria

• Chloroplasts convert light energy to chemical energy (glucose)

• Mitochondria convert chemical energy to ATP (energy transfer molecule)

Ecosystem Energy Flow

• Energy flows into the system as light and out of the system as heat.

• The chemical elements essential to life are recycled.
  Photosynthesis Plants only
  Cellular Respiration Plants and animals

Photosynthesis – An overview

• Converting light energy to chemical energy.

• Occurs in two stages and requires different compartments:

  • The Light Reactions occur in the thylakoid.

  • The Calvin cycle occurs in the stroma.

• Overall goal is creation of glucose.

Photosynthesis: Stage 1 Light Reactions

• In the thylakoid

  • Light energy is captured by chlorophyl pigments in Photosystem II and two electrons are sent down the electron transport chain.

• The cytochrome complex pumps protons into the thylakoid space for ATP Synthase to use when making ATP.

• Photosystem I accepts electrons from cytochrome C and captures more light energy.

• NADP+ is the terminal electron acceptor – ends the electrons’ movement down the chain.

• NADPH is formed by adding an electron and an H+ to an NADP+.

Photosynthesis: Stage 2 Calvin Cycle

• In the stroma.

• Uses ATP and NADPH from the light reactions to build organic carbohydrates (sugars).

• Easiest to think about “three turns” at once.

  • Carbon Fixation: 3 CO2 molecules are each attached to a 5-carbon sugar, making three 6-carbon sugars.

  • Reduction Phase: uses ATP and NADPH to convert all these 3-carbon sugars to a different 3-carbon sugar, known as G3P.

  • One G3P sugar leaves the Calvin cycle at this stage – joins with another G3P sugar outside the cycle to form glucose.

  • Regeneration Phase: uses ATP to rearrange the five 3-carbon sugars into three 5-carbon sugars to “reset” the cycle.

Photosynthesis: Summary

• Light Reactions (stage 1) occurs in the thylakoid.

  • Uses light energy to excite electrons.

  • Two electron transport chains involved.

  • Produces some ATP and NADPH.

  • Breaks down H2O into ½O2 and 2H+.

• Calvin cycle (stage 2) occurs in the stroma.

  • Converts CO2 to a 3-carbon sugar that can be converted to glucose.

  • Uses ATP and NADPH from the light reactions.

  • Can proceed in the dark, but only when there is enough ATP and NADPH.

  • When this supply runs out, the Calvin cycle stops until the light reactions begin again.

Cellular Respiration – An Overview

• Harvesting chemical energy from glucose.

• Occurs in three stages and requires different compartments:

  • Glycolysis occurs in the cytosol.

  • Citric acid cycle occurs in the mitochondrial matrix.

  • Oxidative phosphorylation occurs in the intermembrane space across the inner membrane.

• Overall goal is creation of ATP.

Energy Molecules: ATP and ADP

• ATP (adenosine triphosphate) is our major energy transfer molecule.

• Cellular respiration converts energy from glucose to ATP for our cells.

• ATP cannot be stored, it must be made as it is needed.

• Energy is released upon breaking of the phosphate bonds in ATP.

• Converts ATP to ADP (adenosine diphosphate).

• ATP to ADP releases energy that drives cellular work – transport, growth, etc.

Energy Molecules: NADH and FADH2

• High energy electron carriers.

• Electrons are added in the form of added H+.

• Involved in redox (reduction/oxidation) reactions

• Oxidation is the loss of electrons (or loss of hydrogen).
  - Oxidised form: NAD+ or FAD.

• Reduction is the gain of electrons (or gain of hydrogen).
  - Reduced form: NADH or FADH2.

Cellular Respiration: Stage 1 Glycolysis

• In the cytosol.

• Glucose (sugar) is converted to two smaller molecules of pyruvate.

• Generates:
  - Small amount of ATP (energy molecule).
  -Electrons are transferred to the high energy electron carrier (NAD+), making NADH.

Cellular Respiration: Stage 2 Pyruvate Oxidation and Citric Acid Cycle

• In the mitochondrial matrix.

  • Pyruvate oxidation:

  • Pyruvate is converted into Acetyl CoA (a 2-Carbon molecule)

    • Citric acid cycle:

  • Acetyl CoA enters the citric acid cycle

  • A series of reactions happen resulting in release of CO2

  • Generates:

    • A small amount of ATP (energy molecule).

    • High energy electron carriers NADH and FADH2.

Cellular Respiration: Stage 3 Oxidative Phosphorylation

• In the inner membrane of the mitochondrion.

• Uses the intermembrane space.

• Two parts:

  • Electron transport chain Energy from electrons in NADH and FADH2 used

  • Chemiosmosis - ATP production

Cellular Respiration: Stage 3(1) Electron Transport Chain

• Electron carriers (NADH and FADH2) shuttle electrons to the inner mitochondrial membrane.

• Electrons move along proteins embedded in the inner membrane.

• Electrons lose energy as they are passed along the electron transport chain.

• Energy released is used to pump protons (H+) across inner membrane into the intermembrane space.
  -Protons (H+) accumulate in the intermembrane space – forming a gradient.
  -Oxygen is the terminal electron acceptor – ends the electrons’ movement down the chain.
  -Water is formed by adding the electrons to two H+ and an O.

Cellular Respiration: Stage 3(2) Chemiosmosis

• The electron transport chain forms a proton gradient. More protons in intermembrane space than the mitochondrial matrix

  • The inner mitochondrial membrane contains ATP synthase (protein complex).

• Protons move down concentration gradient through ATP synthase.

• This powers ATP synthesis.

Cellular Respiration: Summary

• Glycolysis (stage 1) occurs in the cytoplasm.
  -Converts glucose to pyruvate.
  -Produces some ATP and NADH
  -Citric acid cycle (stage 2) occurs in the mitochondrial matrix.
  -Further breaks down pyruvate (to CO2).
  -Produces some ATP, NADH, and FADH2.
  -Oxidative phosphorylation (stage 3) occurs on the inner membrane.
  -1. Electron transport chain
  -Electrons from glycolysis and the citric acid cycle enter the electron transport chain (via NADH and FADH2).
  -Energy is released as electrons pass along the electron transport chain.
  -Released energy is used to pump H+ into the intermembrane space, forming a proton gradient
  -2. Chemiosmosis (H+ moves down its concentration gradient through ATP synthase (facilitated diffusion)
  -This drives the production of ATP (much more than stages 1 & 2).