Unit book

• Eukaryotic Cells (vs prokaryotic)

  • Larger cells (>10μm)
  • Often multicellular
  • Always have a nucleus & other membrane-bound organelles
  • DNA is linear and associated with proteins to form chromatin
  • Ribosomes are more dense/ (microtubules + protein strands)
  • Always have an exoskeleton
  • Motility by flexible waving cilia or flagellae (made of tubulin)
  • Cell division by mitosis or meiosis
  • Reproduction is sexual or asexual
  • Common metabolic pathways
• Prokaryotic cells (vs eukaryotic)

  • Small cells (<5μm)
  • Always unicellular
  • No nucleus or any membrane-bound organelles
  • DNA is circular, without proteins
  • Ribosomes smaller/not as dense
  • Motility by rigid rotating flagellum (made of flagellin)
  • Cell division is by binary fission
  • Reproduction is always asexual
  • Huge variety of metabolic pathways
• Metabolic

  Total of all the anabolic (building up ∴ condensation) and catabolic (breaking down ∴ hydrolysis)
• Metabolic pathway

  Chemical reactions in cells e.g. respiration
• Cytoskeleton

  Microtubules + protein strands crisscrossing inside cells, holding organelles in place, cell transport inside cell
• Nucleus S&F

  Structure: Spherical; contains nucleolus, and is surrounded by a nuclear envelope containing nuclear pores

  Function: Contains genetic info in form of DNA & chromosomes which can be transmitted to next gen, Contains ribosomal subunits, mRNA, rRNA, tRNA, Controls activities of cell
• Nuclear Envelope S&F

  Structure: Double membrane embedded with nuclear pores. Continuous with RER

  Function: Separates nucleus from the rest of the cell
• Nuclear Pore S&F

  Structure: Channel proteins in the nuclear envelope

  Function: produces ribsomes
• RER S&F

  Structure: Network of flattened membrane-bound sacs called cisternae, and tubules. Studded with ribosomes. Folded to provide large SA

  Function: Synthesis & transport of proteins + glycoproteins
• SER S&F

  Structure: Network of flattened membrane-bounds sacs called cisternae, and tubules

  Function: Synthesis, storage & transport of lipids, steroid and carbohydrates
• Ribosomes S&F

  Structure: Made of rRNA and proteins. 2 subunits; 1 large, 1 small

  Function: Site of protein synthesis
• Golgi Apparatus S&F

  Structure: Stack of flattened membrane-bound sacs called cisternae

  Function: Modifies & packages proteins & lipids for transport, Used in secretion, Used in lysosome formation
• Mitochondrial S&F

  Structure: Double membrane, Inner is folded to form cristae, Contains a matrix

  Function: Site of aerobic respiration, formation of ATP

  
• Chloroplast S&F

  Structure: Double membrane, Contains thykaloid discs which form stacks called grana, Contains a stroma

  Function: Site of photosynthesis

  
• Cytoplasm S&F

  Structure: A fluid-like substance between the cell membrane and nucleus. Mainly composed of water, as well as some organic and inorganic substances

  Function: Site of chemical reactions, Contains a network of threads and microtubules that help the cell maintain its shape and form
• Plasma membrane S&F

  Structure: Membrane around and within all cells. Composed of phospholipids, proteins, cholesterol, glycolipids and glycoproteins

  Function: Selectively permeable, Controls exchange between cell and environment
• Lysosome S&F

  Structure: Formed from golgi vesicles

  Function: Contain hydrolytic enzymes which break down organelles/ cell debris/ digested materials
• Vacuole S&F

  Structure: Fluid-filled sac bound by a single membrane-tonoplast. Contains sugars, salts, amino acids, waste and sometimes pigment

  Function: Provides structure to plants through making cells turgid, Temporary food store. Provides colour to plants attracting insects
• Cell Wall S&F

  Structure:

  • Plants and Algae- made of cellulose microfibrils
  • Fungi- made of chitin
  • Prokaryotes- made of murein/peptidoglycan

  Function: Freely permeable. Provides support and mechanical strength. Maintains cell shape. Prevents cell bursting when turgid
• Organelles involved in protein synthesis

  1. DNA in the nucleus carries the code for protein
  2. Ribosomes/RER produce protein
  3. Mitochondria produce ATP for protein synthesis
  4. Golgi Apparatus modifies + packages proteins (e.g. carb added to produce glycoprotein)
  5. Vesicles transport modified protein
  6. Vesicles fuse with cell-surface membrane
  7. Protein is released by exocytosis at cell membrane

  
• Binary fission

  1. The circular DNA molecules replicates and both copies attach to the cell membrane
  2. The plasmids also replicate
  3. The cell membrane begins to grow between the two DNA molecules and begins to pinch inwards, dividing the cytoplasm in two
  4. A new cell wall forms between the two molecules of DNA, dividing each of the cells into two identical daughter cells, each with a single copy of the circular DNA and variable numbers of plasmids

  
• How does HIV replicate

  1. Virus attaches: Attachment proteins on the HIV surface "dock" with CD4 receptors on the target T-helper cell
  2. Genes copied: HIV uses enzyme reverse transcriptase to make a single strand of DNA from its RNA. The human cell then makes a complementary strand to the HIV DNA
  3. Replication of nucleic acid: Virus inserts this copy into host cell's DNA & is transcribed to mRNA: mRNA uses the cell's protein synthesis mechanisms to make the HIV Virus components
  4. Release of HIV particles: The parts are assembled and form a "bud", which breaks off to become a new HIV virus

  
• Methods of studying cells

  • Cell fractionation
  • Light microscope
  • Electron microscope (TEM, SEM)
• How does cell fractionation work?

  1. Cell fractionation - tissue cut into small pieces (minced) & placed into cold, isotonic, buffer solution
  2. Then ground into smaller pieces using homogeniser: releases organelles from the cell
  3. Homogenate filtered to remove complete cells & large debris e.g. cell wall
  4. Suspension of homogenate is placed in a test tube and spun (^ force,^ speed)
  5. @ slower speeds large fragments collect at bottom, smaller ones at top in liquid called SUPERNATANT LIQUID
  6. Larger fragments (sediment pellets) are removed from supernatant, respun at faster speeds (process repeats)

  
• Why homogenate must be

  1. Cold- To reduce activity of enzymes that break down organelles
  2. Isotonic- To prevent bursting or shrinking due to osmosis
  3. Buffered- To prevent pH fluctuations altering organelle & enzyme activity
• Image


  Appearance of an object or material when viewed under a microscope
• Object

  The material that is put under a microscope
• Resolution

  The minimum distance apart that two objects can be in order for them to appear as separate items
• Magnification

  How many times bigger the image is when compared to the object
• Microscope equations

  • Magnification = image size ÷ actual size
  • Total Magnification = total Magnification of eyepiece lens × total Magnification of objective lens
• Light vs electron microscope

  Light:

  • Small & portable
  • Maximum magnification ×1500
  • Maximum resolving power (add digits)
  • Can view thin sections of plants & animals

  Electron:

  • Cannot observe living material (vacuum)
  • Complex preparation & staining process
  • High resolution (electrons) and magnification
  • Metal salts used as a stain to scatter electrons
• TEM Advantages & Disadvantages

  TEM:

  ✓ Can see internal details of cell/ultrastructure

  ✓ Higher resolution of magnification than SEM

  ✘ Vacuum

  ✘ Complex staining method

  ✘ Artefacts may be present

  ✘ 2D imagine only

  ✘ V. thin specimen required
• SEM Advantages & Disadvantages

  ✓ 3D image

  ✓ Shows the surface of the specimens

  ✓ Do not need v. thin sections

  ✘ Vacuum

  ✘ Complex staining method

  ✘ Lower res. and mag. compared to TEM
• Fluid Mosaic Model of the cell membrane

  
• Phospholipid bilayer role in cell membrane

  • Selectively/partially permeable
  • Allow small, non-polar, lipid-soluble molecules to enter and leave cell
  • Make membrane flexible and self-sealing/ able to form vesicles
• Glycoprotein role in cell membrane

  • Cell recognition site for cell signalling
  • Identification
  • Receptors e.g. bind to hormones
  • Allows cell to attach to one another and form tissues
• Glycolipid role in cell membrane

  • Cell recognition sites for cell signalling
  • Allows cells to attach to one another & form tissues
• Channel protein role in cell membrane

  • Protein which creates water-filled hydrophilic channel through which ions can pass
• Carrier protein role in cell membrane

  • Protein which changes shape to allow larger molecules to pass through the membrane
  • Allows active transport across the membrane
• Cholesterol role in cell membrane

  • Prevents leakage of water and dissolved ions from the cell
  • Reduces lateral movement of other molecules e.g. phospholipids
  • Makes membrane less fluid at high temperatures