Chapter 2
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Transcript of Chapter 2
Chapter 2Membranes and cell organelles
The plasma membrane
7-9nm thick (nucleus & ER membranes = 5-7nm)
All biological membranes are the same : fluid-mosaic model phospholipid bilayer, proteins, carbohydrates and cholesterol
Membranes are fluid structures - individual lipid molecules & some proteins move about within the layers
Phospholipids Hydrophobic tails will face away from water to form a monolayer or micelle (if tails
are short) Therefore membrane is impermeable to water soluble (polar) molecules
Proteins carry out most other membrane functions, they are located throughout the membrane (hence the term mosaic) can cross both layers OR be confined to one Provide channels for water-soluble molecules & ions to pass
Cholesterol (between the phospholipid molecules) makes the membrane less fluid & more stable
Carbohydrates are usually on the outer surface & linked to protruding proteins
Membranes
Diffusionthe passive, net (overall) movement of
particles from a region of relatively high concentration to a region where they are at a relatively low concentration. O2 CO2 N2 H2O Ethanol Glycerol
Concentration gradient: (diffusion gradient) the steeper the gradient, that more rapid the rate of diffusion. As the gradient declines, diffusion slows down until it
reaches equilibrium (particles move to and fro at the same rate in all directions)
Osmosis (special kind of diffusion)
the diffusion of water molecules from one
solution to another of different concentration
through a selectively permeable membrane
OR
the net overall movement of water molecules
across a selectively permeable membrane from
a dilute solution (high concentration of water
molecules + low concentration of solute
particles) to a concentrated solution
Solute
Solvent(eg. Water)
Isotonic: (iso - same) surrounding fluid and cells internal fluid are of equal concentration
Hypotonic: (hypo - lower) surrounding solution has a lower concentration than the cells.Water will diffuse through the membrane into the cells
• Hypertonic: (hyper - higher) surrounding solution has a higher concentration than the cells
Channel/Carrier mediatedChannel mediated: free passage across the
membrane with the assistance of protein channel
Carrier mediated: Larger polar & non-polar molecules like glucose need proteins to carry them through: facilitated diffusion
Active transportThe net movement of dissolved substances
into or out of cells against a concentration gradient
This process requires energy
Mitochondrion
Golgi apparatus
Centriole
smooth ER
Lysosome
Cytoplasm/Cytosol
Plasma membrane Cell Wall
Ribosome
rough Endoplasmic Reticulum (ER)
Nucleus
nuclear pore
nucleolus
nuclear membrane
Cytoplasm / CytosolCytoplasm
contents of the cell (without nucleus) 90% water + ions, salts, enzymes, food
molecules & organelles
Cytosol fluid component of cytoplasm in which
organelles are located
Cytoplasm/Cytosol
Nucleusdouble membrane = nuclear envelope = eukaryote
lacking nuclear envelope = prokaryote
granular DNA until mitosis, then DNA becomes
organised into chromosomes
nucleolus/ nucleoli = aggregation of RNA
controls cellular activities
nuclear pores to allow movement between
Nucleus
nucleus and cytoplasm
Mitochondrionproduces chemical energy in the form of adenosine
triphosphate (ATP) through the process of cellular
respiration
outer & inner membrane
ATP produced by reactions on inner membrane
only in eukaryotes
Mitochondrion
Ribosome
protein factories = synthesis of polypeptides
in the cytosol or associated with ER
are made of protein and rRNA (ribosomal
RNA)Ribosome
Endoplasmic reticulum (ER)network of intracellular membranes
production, processing, transport & storage of
materials within a cell
links with plasma membrane and other
membranous organelles rough ER
smooth ER
Golgi apparatus
stack of flat membrane sacks
final synthesis & packaging of proteins
into membrane-bound vesicles before
secretion
Nature of Bio p. 47
Golgi apparatus
Lysosomes
contain powerful enzymes to break down
debris & foreign material
membrane bound & in most animal cells
Lysosomes
Plant cell
c
c
c
c
Cell Wall (not an organelle)plant & bacterial cells
non-living cellulose (chitin for bacteria)
provides support, strength & prevents
expansion
freely allows water & dissolved substances
through
cc
Chloroplastsgreen organelle (due to lots of chlorophyll)
found in most plant cells
many folded membranes
site of photosynthesis
c
Vacuolesmembrane bound, liquid filled spaces
food vacuoles (intracellular digestion)
contractile vacuoles (water balance)
plant cells typically have large ones filled with sap
(turgidity & storage)
tonoplast vacuole membrane in plant cellc
Other OrganellesPeroxisomes
detoxify various toxic materials that enter the bloodstream (ie: alcohol)
Endosomes pass newly ingested material to lysosomes for digestion
Centrioles small pair of cylindrical structures composed of microtubules involved in separating chromosomes during mitosis in animal and
protist cells (not in plants)
Cilia & Flagella used for movement in many prokaryotic cells & some eukaryotes covered by an extension of the cell membrane made up of 9 doublet microtubules & 2 single, central microtubules
Apoptosis / Programmed cell death
Neat cell death - unlike Necrosis
1. Many different caspases are
activated
2. Cell begins to shrink and
develop small bumps
3. Caspases cause DNA and
proteins to degrade and
mitochondria to break down
4. Phagocytosis of parts,
components recycled
The cell skeletonMaintain the shape of the cellProvide a support structure for other components in cellMovement of materials within cellMovement of the cell itself - if required
Occluding (Tight) junctionsCell membranes “come
together”Function:
hold cell togetherhelp to maintain polarity
of cellprevent passage of
molecules
NO movement of material between cells
Communicating (gap) junctionsProtein-lined pores in
the membranes of adjoining cells
Permit the passage of: amino acids, sugars, salt ions, and other small molecules
Anchoring junctions (Desmosomes)Dense plaques of protein with fine fibrils
Serve as a bridge connecting the actin cytoskeleton of neighbouring cells
Connections between plant cells: plasmodesmata
Chapter Review QuestionsChapter Review Questions: 2, 3, 4, 5, 7, 8 &
10 due on Monday 15th February
Biozone .... due on