Unit 1: Cells (copy)

Cells

Basic structural unit of all living organisms

Cell Theory

1. Cells are SMALLEST unit of life

2. Organisms are made of ≥1 cell

3. Cells arise from pre-existing cells

Structures common to cells in all living organisms + Reasons

• Cell Membrane

  Phospholipids spontaneously arrange into a bilayer

  Encloses cell + Protects contents from environment

  Controls interactions between cell contents and exterior (Signalling & transport)

• Cytoplasm

  Mainly water matrix called cytosol (Contains all ingredients i.e. carbon compounds, ions + Provides medium for metabolic reactions); Responsible for giving cell its shape

• Ribosomes (?)

• DNA

  Able to form large molecules which carries and transfers genetic material between organisms; Controls production of enzyme and proteins within organism

Prokaryotic Cell Structure (HINT: 10 features)

1. Cell wall: Rigid outer layer of peptidoglycan
   Function: Maintains shape and prevents lysis

2. Plasma membrane: Semi-permeable; Selective barrier surrounding cell

3. Naked loop of DNA: Bacterial chromosome; Circular

4. 70S ribosomes: RNA + Protein Complex
   Function: Polypeptide synthesis

5. Cytoplasm: Internal fluid

6. Plasmid: Autonomous circular DNA molecules; Transferrable between bacteria (Horizontal gene transfer)

7. Nucleoid Region: Where DNA is located in cytoplasm; Non-compartamentalized
   Function: Cell control and reproduction

8. Slime capsule: Thick polysaccharide layer
   Function: Protection against desiccation and phagocytosis

9. Flagella: Long, slender projections; Contains motor protein
   Function: Movement

10. Pili: Hair-like extensions
    Function: Attachment pili = Adhesion to surfaces; Sex pili = Bacterial conjugation

Types of Prokaryotic Cell Structure (+ Relevant Examples)

• Gram-positive eubacteria
  Thick peptidoglycan layer
  No outer lipid membrane
  —> Retains crystal violet stain

  Example: Bacillus, Staphylococcus

• Gram-negative

• Phytoplasma

• Mycoplasma

Common Eukaryotic Cell Structures (HINT: 4)

1. Plasma Membrane

2. Cytoplasm

3. 80S Ribosomes

   Bound = Protein synthesis for transport

   Free-moving = Protein synthesis for cell

4. Nucleus

   DNA bound to histones; Contained in a double membrane, nuclear envelope with nuclear pores → Controls movement of molecules between nucleus and cytoplasm

Organelles in Animal / Plant Cells (HINT: 11, 4 special)

• Nucleus

• Mitochondria

  Has its own genome; Reproduce by fission; Double membrane-bound
  Makes energy, stores Ca, Controls cell growth and death

• Rough Endoplasmic Reticulum (RER)

  Surface is covered in ribosomes

  Synthesise proteins for use outside of cell

• Smooth Endoplasmic Reticulum (SER)

  Synthesises lipid and hormones

• Golgi apparatus

  Processing + Secretion of protein; Package proteins and lipids into vesicles for delivery out of cell

  • Transport vesicles are received on cis side

  • Modified as it moves through cisternae + Attachment of signalling chemical which directs it to destination

  • Packaged and transported on trans side

• Vesicles

  Small sacs that transports molecules into cell by fusing with membrane

• Vacuoles

  Small and numerous

  Large space; If central area = Central vacuole

  Store food, toxins, metabolic waste, water + Uptake of water → Rigidity, Provide nutrition

• Lysosomes

  Sacs bound by single membrane

  Contain and transport enzymes

• Cytoskeleton

  System of protein fibres (microtubules and microfilaments)

  Hold organelles in place; Maintain structure and shape of cell

• Centrioles

  At centrosome

  Assembles microtubules for structure & movement + Nuclear division

• Chloroplasts

  A plastid (Organelle for manufacturing / storing energy)

  Converts light to chemical energy via photosynthesis

Kingdoms of Eukaryotes + Differences

• Protista

  Uni OR Multicellular; No specialised tissue

• Fungi

  Chitin cell wall; Nutrition via heterotrophic absorption (Obtain by absorption from environment; Broken down externally)

• Plantae

  Cellulose cell wall; Autotrophic nutrition (Photosynthesis)

• Animalia

  No cell wall; Heterotrophic ingestion for nutrients

Compare & Contrast Prokaryotic and Eukaryotic Cells (Min. 3 for Each)

PROKARYOTES

• Simple structure

• Small size

• Peptidoglycan cell wall

• 70S Ribosomes

• Unicellular

• No membrane bound organelles

BOTH

• DNA

• Ribosomes

• Cell membrane

• Cytoplasm

EUKARYOTES

• Complex structure

• Prominent nucleus

• Large size

• Chitin / Cellulose cell wall (some)

• Uni or Multicellular

• 80S Ribosomes

• Membrane bound organelles

Processes of Life in Unicellular Organisms (HINT: MR H N GERM) + In Paramecium

1. Homeostasis: Maintenance of constant internal environment
   Maintains internal conditions e.g. expel water by contractile vacuoles

2. Metabolism: Chemical reactions within organism
   Produce enzymes to catalyse chemical reactions in cytoplasm

3. Nutrition: Ability to acquire energy to sustain life
   Feeds on smaller organisms by endocytosis (Ingestion and digestion in vesicles)

4. Movement: Ability to move
   Thousands of cilia beat

5. Excretion: Ability to release unnecessary / harmful materials into environment
   Expel metabolic waste (CO₂) from respiration by diffusion

6. Growth: Development
   Increase in size and dry mass by accumulating organic matter and minerals from food

7. Response to stimuli: Include environmental adaptations
   Reverses direction of movement upon contact with solid object

8. Reproduction: Ability to produce offspring
   Asexual reproduction via mitosis or sexual reproduction via meiosis and gametes

Differences in Eukaryotic Cell Structures (Animals, fungi, and plants)

Comment on: Presence and composition of cell walls, differences in size and function of vacuoles, presence of chloroplasts and other plastids, and presence of centrioles and centrosomes, basal bodies, cilia, flagella, and budding scar

• Presence / Composition of Cell Wall
  Fungi: Chitin
  Animal: N/A
  Plant: Cellulose

• Size and Function of Vacuoles
  Fungi: Small and numerous; Degradation of molecules
  Animal: Small and numerous; Store carbohydrates as glycogen
  Plant: Large; Store carbohydrates as starch; Water uptake
  NOTE: Contractile vacuoles in unicellular eukaryotes

• Plastids
  Fungi: Mitochondria
  Animal: Mitochondria
  Plant: Mitochondria, Chloroplasts

• Centrioles
  Fungi: Centrosomes ONLY
  Animal: Yes + Centrosomes
  Plant: Centrosomes ONLY

• Cilia
  Fungi: Some
  Animal: Some
  Plant: N/A

• Flagella
  Fungi: Some
  Animal: Some
  Plant: Some

• Basal Bodies
  Fungi: N/A
  Animal: Yes
  Plant: N/A

• Budding Scar
  Fungi: Yes
  Animal: N/A
  Plant: N/A

Atypical Cell Structures in Eukaryotes (Number of nuclei)

• Aseptate fungal hyphae
  Multi-nucleated, long tube-like structures

• Skeletal muscle: Formed by fusing smaller cells
  Large cells (~30 mm long); Multi-nucleated (Several hundred)

• Red blood cell
  Anucleated → Greater haemoglobin capacity → Transport more oxygen

• Phloem sieve tube elements
  Anucleated → Low resistance for substances moving through

Identify the organelles (1)

Identify the organelles (2)

Draw a labelled diagram of prokaryote (9 features!)

Draw a labelled diagram of animal cell (10 features!)

Draw a labelled diagram of plant cell (11 features!)

How to calculate magnification

Magnification (X) = Image Size (Measured by ruler) / Actual Size

Note: All should be in same units

Developments in Microscopy + Advantages

Light Microscopy: View living specimens in natural colors

Advantages –
Inexpensive, simple and easy specimen preparation, live or dead specimen

• Fluorescent Stains
  Binds specific cellular components to image specific structures; Detailed visibility

• Immunofluorescence
  Uses antibodies conjugated (bound) to fluorescent probes → Specifically target a cellular component; Often used to detect viral proteins in infected cells

Electron Microscope

Advantages –
Over 500,000X magnification, higher resolution

• Scanning Electron Miscrope
  Scatter electrons across surface to differentiate depth → 3D Maps

• Transmission Electron Miscrope
  Pass electrons through specimens → Cross-section Image

• Freeze Fracture Electron Microscopy
  Freeze samples then break sample into small pieces → See internal structure; Visualise structures not normally visible

• Cryogenic Electron Microscopy
  Freeze samples to fix them into firm / stable structure; Improved resolution of image + Reduce damage from electron beam

Origins of Eukaryotic Cells by Endosymbiosis

Larger prokaryotes engulfed smaller ones and formed an endosymbiotic relationship, allowing them to exist inside them. The large one provided protection from environment, and the smaller provided energy.

Evidence for Endosymbiotic Theory

Chloroplasts and mitochondria:

• Have double membranes

• Can replicate via binary fission

• Contain smaller ribosomes

• Have small circular strands of DNA

Cell Differentiation

Process for developing specialised tissues in multicellular organisms

Basis for Differentiation

Different patterns of gene expression triggered by environmental changes

Evolution of Multicellularity

Multicellularity has evolved repeatedly (From prokaryotes → single-celled eukaryotes → multi celled eukaryotes, etc.)

Include fingi, eukaryotic algae, and all plants and animals

Advantages of Multicellularity

Allows larger body size and cell specialization

Properties of Stem Cells

Capable to divide endlessly and differentiate along different pathways

Differences Between Totipotent, Pluripotent, and Multipotent Stem Cells

• Totipotent: Can become any cell type
  Cells in early-stage animal embryos

• Pluripotent: Cab become a range of different checks
  Endoderm, Mesoderm, Ectoderm Line

• Multipotent: Can only become related cell types
  Stem cells in adult tissues e.g. bone marrow

Location and Function of Stem Cell Niches in Adult Humans

Stem cell niche can maintain the cells or promote their proliferation and differentiation

• Bone Marrow
  Can become different types of blood cells

• Hair Follicles
  Produce cells for hair growth, repair, regeneration + Immune cells and nerves

Production of Unspecialised Cells

1. During sexual reproduction, gametes fuse together

2. As a result of fertilisation, a zygote is formed

3. The single-celled zygote divides rapidly and form unspecialised, embryonic stem cells

Impacts of Gradients on Gene Expression (Within early-stage embryos)

Cell’s position in the embryo → Concentration of morphogens → Different gene expression patterns → Forms specialised cell types

• At the anterior of the embryo, low retinoic acid → thyroid development

• At the posterior, high retinoic acid → colon

Cell Size as an Aspect of Specialization

• Sperm (5 μm, 60 μm in length)
  Long flagellum provides propulsion to rapidly reach egg

• Red Blood Cells (7-8 μm in diameter)
  Allows it to manoeuvre through capillaries

• Egg (~100 μm in diameter)
  Contain many nutrients

• Striated Muscle Fibres (narrow - 20-100 μm, long - 10 cm)
  Coordinate contraction + Significant muscle force generation

• Neurons (narrow - 10 μm, long - 1 m)
  Efficient and rapid transmission of nerve impulses from brain to spinal cord to muscles for movement

Surface Area to Volume Ratio

Large SA:Vol ratio → decrease rate of exchanges → Divide to maintain low SA: Vol ratio

• Entry and exit of substances in cell; Rate of exchange

• Movement of substances within cell from one end to another

Adaptations to Increase SA:Vol Ratios in Cells + Examples

• Flattening of cells

  Erythrocytes: High SA:Vol ratio → Large SA for oxygen to bind to hemoglobin

• Microvili

  Apical surface (facing lumen / inside) of proximal convoluted tubule: Large SA to maximize absorption and secretion of solutes (Na⁺, Cl^-, glucose, etc.)

• Invagination

  Basal side (facing blood at base of cell) of proximal convoluted tubule: Increase rate of solute transfer from epithelial cells into blood

Adaptation for Type I and Type II Pneumocytes in Alveoli

Type I Pneumocytes (~5%)

• Extreme thinness + Squamous → Reduce distance for diffusion

Type II Pneumocytes (~95%)

• Presence of many lamellar bodies (secretary vesicles) in cytoplasm to discharge surfactant to alveolar lumen → Prevent alveolar walls sticking together; Reduce surface tension

Adaptations of Cardiac Muscle Cells and Striated Muscle Fibres

Both have contractile myofibrils

Cardiac muscle cells

• Branched → Create space between muscle cells → Flexible; Allow rapid heart pump

• Short cells; One nucleus → Synchronised contractions

• Intercalated discs → Facilitate rapid signal transmission → Coordinated contractions + Strong cell-to-cell adhesion → Structural integrity during pumping

Striated muscles (Connected to skeleton)

• Unbranched → Provides strength

• Long cells → Increase overlap of myosin (converts chemical to mechanical energy) + Actin (for muscle contraction) → Generate movement

• Multinucleated → Support constant need for protein production + Tissue repair

Adaptations of Sperm and Egg Cells (HINT: 6 for sperm,

Sperm

• Enzymes in acrosome (head) region → Help with entry

• Streamline shape → Speed and movement

• Lots of mitochondria → Produce ATP for energy to swim

• Flexible microtubules in tail → Swimming

• Lack of other organelles → Conserve energy to fulfil function

• Small size (See before) → Travel efficiently and attach to surface of egg

Egg

• Zona pellucida and cortical granules (cell membrane structures) undergoes chemical reactions when sperm enters → Prevent additional sperm from entering

• Lots of mitochondria → Produce energy

• Cytoplasm contains many nutrients → Support growth of early embryo; Acts as stored food supply

• Large SA and size (See before) → Facilitate more opportunities for sperm to enter

Behaviour of Phospholipids and Amphipathic Lipids in Water

Naturally form continuous sheet-like bilayers

How do membranes function as effective barriers between aqueous solutions?

Hydrophobic hydrocarbon chains have LOW permeability to large molecules and hydrophilic particles (IONS, POLAR molecules)

Example of Simple Diffusion Across Membranes

Due to phospholipid bilayers being selectively permeable, only oxygen and carbon dioxide molecules and other small, non-polar molecules are able to pass through between phospholipids

Diverse Structures, Locations, and Functions of Membrane Proteins (HINT: TRACIE)

Integral Proteins (Embedded; Amphipathic; Mono- or polytonic i.e. penetrating one or two layers)

• α-helix: For recognition (Receptors)

• Helical bundle: Enzymes, transporters, receptors

• β-barrel: For transport (Channel proteins)

Peripheral Proteins (Monotopic or surface only; Usually anchored to an integral protein)

• Enzymes, transporters, anchorage

Function:

1. Transport

2. Receptors

3. Anchorage

4. Cell recognition

5. Intracellular joints (Junctions between cells)

6. Enzymes

Osmosis and Role of Aquaporins

Passive movement of water across a selective permeable membrane

Occurs due to differences in solute concentrations; Movement occurs until concentrations are equal → Changes cell size

• Hypertonic = High solute concentration environment

  Plasmolysed cells; Water moves out of cell

• Isotonic = Equal solute concentration environment

  Normal cells; No net movement

• Hypotonic = Low solute concentration environment

  Turgid cells; Water moves into of cell

Aquaporins (Integral protein) = Water Channels

• As polar molecules cannot pass quickly through membrane, aids faster water transportation in response to solute concentrations

How does the structure of channel proteins make membranes selectively permeable? (Channel & Carrier proteins)

They allow specific ions to diffuse through channels are open and not when they are closed.

Channel proteins

• Have pores → Allows specific size + charge of molecules pass

• Carry only water-soluble molecules; Specific to ions

• Close and open in response to electrochemical / mechanical signals

Carrier proteins

• Changes shape to carry ion across membrane

• Can transport along (Facilitated Diffusion) OR against concentration gradient (Active Transport)

Types of Cellular Transport

Passive

• Simple diffusion

• Facilitated diffusion

  Carrier proteins

Active

• Pump

  Carrier proteins

Active transport (Pump proteins)

Protein pumps = Globular proteins; Embedded in membrane

• Uses ATP to transfer specific particles across membrane; Movement against concentration gradient

Example of Pump Protein (Sodium-Potassium pump)

Selectivity in Membrane Permeability

Allow selective permeability in membrane:

• Facilitated diffusion

• Active Transport

Not selective; Depends only on size and polarity of particles:

• Simple diffusion

Structure and Function of Glycoproteins and Glycolipids

Glycoproteins: Cell membrane proteins attached to carbohydrate chains

Glycolipids: Phospholipids attached to carbohydrate chains

• On extracellular side of membrane

• Assist in cell identification + Adhesion

  E.g. antigens on blood types

Draw a diagram of the Fluid Mosaic Model of Membrane Structure

Include:

• Peripheral + Integral proteins

• Glycoproteins

• Phospholipids

• Cholesterol

+ Indicate hydrophobic + hydrophilic regions

Relationships between fatty acid composition of lipid bilayers and their fluidity

Unsaturated fatty acids (kink) in lipid bilayers → Lower melting points → Fluid → Flexible at temperatures experienced by a cell

Saturated fatty acids (straight) → Higher melting points → Stronger at high temperatures

Example of adaptions in membrane composition in relation to habitat

In unicellular organisms, e.g. bacteria

• Have fatty acid desaturase → Speed up reactions; Increase double bonds in fatty acid tails → More unsaturated fatty acids → More flexible structure at different temperatures → Able to withstand changes in temperature

Cholesterol and Membrane Fluidity in animal cells 

Acts as a modulator of membrane fluidity → Stabilises membrane at higher temperature / Prevents stiffening at lower temperatures

Many are embedded in membranes

Endocytosis and Exocytosis + Examples

Endocytosis

• Invagination of membrane / Membrane is pinched into a vesicle forms flask-like structure → Envelops substances into vesicle; Brings materials into cell

  1. Phagocytosis: Large cells & Particles

  2. Pinocytosis: Water & Liquids

  3. Receptor-mediated: Specific molecules

Exocytosis

• Vesicles containing substances from Golgi apparatus travels to membrane → Fuses to bilayer → Releases contents to environment

  1. Insulin released into bloodstream by pancreatic cells

  2. Neurotransmitters released at synapses

Note: Fusion of vesicles in exocytosis ADDS phospholipids to bilayer which offsets those TAKEN during endocytosis

Types of Gated Ion Channels + Examples

Facilitated diffusion; Gated = Open/close in response to chemical or mechanical stimuli

Voltage-gated Ion Channels

• Sodium / Potassium Channels

  1. Sodium ions bind to protein pump and move into neurone; Depolarises membrane

  2. Potassium channels open → Potassium ions move outside of cell; Repolarization

Ligand-gated Ion Channels (Neurotransmitters)

• Nicotinic Acetylcholine

  1. Acetylcholine binds to a receptor protein on the postsynaptic neurone

  2. Conformational change to channel

  3. Opens channel; Sodium, potassium, and calcium ion to diffuse into cytoplasm of postsynaptic neurone (along electrochemical gradient)

  4. Makes the inside of postsynaptic neurone relatively positive (depolarised) and generates impulse

Exchange Transporters (Sodium-Potassium Pumps)

Helps maintain membrane resting potential

Moves ions against concentration gradient (Movement TOWARDS HIGH solute concentration)

• Generally, cells are more negative inside than outside cell

  1. Initially open on intracellular side of cell

  2. THREE sodium ions bind to pump protein → Phosphorylates it; Changes configuration

  3. Pump opens to extracellular side

  4. Sodium ions are released; TWO Potassium ions bind

  5. Pump is dephosphorylated; Reverts configuration

  6. Potassium ions are released into intracellular matrix

• More potassium ions INSIDE cell; More sodium ions OUTSIDE cell

• Net Movement = Potassium ions leak OUT; Sodium ions leak IN through leakage channels

  NOTE: More potassium leakage channels → More permeable to potassium at rest → More potassium leak out → Relatively negative charge inside cell

Indirect Active Transport (Sodium-Dependent Glucose Cotransporters)

• Used for glucose (re)absorption by cells in small intestine and nephron

1. Sodium-potassium pump uses ATP to create electrochemical gradient of sodium ions (High conc. OUTSIDE cell; Low conc. INSIDE cell)

2. Two sodium ion and one glucose molecule binds to a cotransporter

3. Ions are transported across membrane ALONG its gradient, carrying glucose molecules as well AGAINST its gradient

Cell-Adhesion Molecules

Different types of CAM → Different types of cell to cell junctions

• Desmosomes
  Form sturdy + flexible sheets of cells in organs → Hold cells together in tissues during stretching

• Plasmodesmata (Plants)
  Tubes connecting cytoplasm of adjacent cells → Exchange materials i.e. water, small solutes

Conditions on Early Earth and the Prebiotic Formation of Carbon Compounds

• Lack free oxygen → Absence of ozone layer

• Higher concentrations of CO₂ and CH₂ → Higher temperatures + UV light penetration

Caused a variety of carbon compounds to form spontaneously by chemical processes that no longer occur

Smallest units of self-sustaining life

Cells

Differences between living and nonliving (Why are viruses non-living?)

Viruses…

• Cannot metabolise

• Cannot perform homeostasis

• Cannot move

• Cannot grow

• Cannot reproduce independently

• Cannot excrete metabolic waste

• Cannot intake nutrients

Spontaneous Origin of Cells

Cells = Highly complex structures; Only produced by division of pre-existing cells

Requirements for Evolution of First Cells

• Catalysis

• Self-replication

• Self-assembly

• Emergence of compartmentalisation

Evidence for Origin of Carbon Compounds

Miller-Urey Experiment

Simulated early Earth conditions; Showed organic compounds (hydrocarbons, amino acids) can be formed from inorganic precursor molecules

• Water = Ocean

• Gas inlet = Addition of methane, ammonia and hydrogen

• Heat = Produce water vapor

• Electrical sparks = Electrical storms

Criticism of Miller Urey Experiment

Earth’s early atmosphere was different from the composition of gases used in experiment

Glassware, medium of experiment, could have reacted

Formation of Vesicles

By coalescence (merging) fatty acids into spherical bilayers

• Needed to allow internal chemistry to become different from outside of compartment

RNA as Presumed First Genetic Material (HINT: 2 Points)

RNA can…

• Be replicated

• Has some catalytic activity

  (Both genetic material + enzyme)

  
  

Ribozyme in ribosome catalyses peptide bond formation during protein synthesis

Evidence for Last Universal Common Ancestor (LUCA)

Universal genetic code

Shared genes across all organisms

• Other forms of life may have evolved but became extinct due to competition from LUCA and its descendants

Approaches Used for Estimation Dates

Studying fossils via radiometric techniques based on half-life of radioactive isotopes

Genetic dating / Analysis

Evidence for Evolution of LUCA Near Hydrothermal Vents

Fossilised evidence of life from ancient seafloor hydrothermal vent precipitates

Evidence of conserved sequences from genomic analysis; Common genetic sequences in organisms near vents → Suggest single ancestor

Presence of mineral-rich environment + Necessary acidic/basic fluids for chemical reactions

Presence of hydrogen and CO₂ → Reducing environment for carbon compound formation

Organelles

Discrete subunits of cells; Adapted to perform specific functions

Which cell components ARE and ARE NOT considered organelles? (HINT: 3 & 4)

NOT considered:

1. Cell wall

2. Cytoskeleton

3. Cytoplasm

   
   

CONSIDERED:

1. Nuclei

2. Vesicles

3. Ribosomes

4. Plasma membrane

5. Cilia/Flagella

6. Golgi apparatus

7. Mitochondria

8. Chloroplasts

9. Lyososomes

Advantage of Separation of Nucleus and Cytoplasm into Separate Compartments

Separates activities of gene transcription and translation

• Allows for post-transcriptional modification of mRNA before it meets ribosomes in cytoplasm → More possibilities for protein synthesis (this is what I think, not in syllabus)

In prokaryotes, mRNA immediately meet ribosomes (due to lack of separation)

Advantages of Compartmentalisation in Cytoplasm of Cells + Examples

Allows for…

• Appropriate concentration of metabolites for optimized function

  Pancreatic cells have lots of rough ER → Export many proteins

  Liver cells have lots of smooth ER → Break down toxins

• Separation of incompatible biochemical processes

  Lysosomes + Phagocytic vacuoles = Contain hydrolytic enzymes → Digest cellular debris / Engulf pathogenic materials (Prevents autophagy)

Adaptation of Mitochondria for Production of ATP (HINT: 5 features)

Double membrane

• Separates contents of mitochondrion from rest of cell

• Outer membrane: Contains transport proteins to move pyruvate into mitochondrion

• Inner membrane: Contain ATP synthase required to generate ATP

Small volume of inter membrane space

• Allows for a high concentration of proton to fill up quickly → ETC

Large SA in cristae

• Tubular regions surrounded by membrane

• Increase SA for ETC and ATP syntheses → Increased ATP production

Compartmentalisation of enzymes

• Optimise pH conditions for enzymes in Krebs cycle

Substrates of Krebs cycle in matrix

• Enzymes for first stage respiration (Link reaction + Krebs cycle)

Adaptations of Chloroplast for Photosynthesis (HINT: 3 features)

Large SA of thylakoid membranes

• Greater absorption of light by PS

Small volumes of fluid inside thylakoid

• Faster accumulation of protons to create concentration gradient

Compartmentalisation of enzymes and substrates of Calvin cycle in stroma

• Store appropriate enzymes + Optimised pH conditions for them to work in Calvin cycle

Functional Benefits of Double Membrane of Nucleus

Nuclear pores = Channel proteins

• Controls entry and exit of signalling molecules and transcription factors → Regulation of gene expression

During mitosis and meiosis (cell division)…

• Nucleus membrane breaks down to let chromosome separate / movement of DNA structures

• When finished, vesicles from ER (with specific lipids and proteins) bind to chromosome → Reform nuclear envelope

Structure and Function of Vesicles

Membrane-bound sacs containing substances for transport or storage

• Peroxisomes, lysosomes, transport vesicles, secretory vesicles

Formation of vesicles (Selective and efficient)

• Clathrins line coated pits; Specific proteins bind to receptors and become anchored at that site

• Forms cage-like structure by polymerisation

• Cathrin surrounds membrane invagination → Forming clathrin-coated pit

• Eventually seals off to become a vesicle