the living cell is a miniature factory where thousands of reactions occur – converts energy in...
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The living cell
Is a miniature factory where thousands of reactions occur
– Converts energy in many ways
Figure 8.1
Bioluminescence
Metabolism
– Is the totality of an organism’s chemical reactions
– Arises from interactions between molecules
– An organism’s metabolism transforms matter and energy, subject to the laws of thermodynamics
Molecular Factory
• Factories are highly ordered systems which have an input of materials, energy requirements and an expected output
• There is a design to factories- you don’t get automobiles from a Barbie factory…
Cells as factories
• Cell has three main functions– Make a product through a series of highly ordered
steps and guided via an enzymatic and biofeedback process
– Maintain balance– Reproduce
All parts of the cell play a role in maintaining the cellular factory.
Size range of cells
The Nucleus and Ribosomes
Nucleus- enclosed by nuclear envelope- contains most of the genes that control the entire cell
+ DNA organized with proteins into chromatin
- nucleolus
Nuclear lamina – protein filamentsthat give structure to the inner nuclear membrane
The Nucleus and Ribosomes (con’t)
Ribosomes- build proteins- RNA/protein complexes- free/bound
The Endomembrane SystemIncludes:•nuclear envelope
•Endoplasmic reticulum
•Golgi apparatus
•Lysosomes
•Vacuoles
•Plasma membrane*
Mitochondria and Chloroplasts•energy transformers of cells + double membranes + contain ribosomes/DNA
Mitochondrial DNA is only passed on by mom
The Cytoskeleton
Cytoskeleton•provides structural support for motility and regulation + network of fibers
- microtubules - microfilaments
- intermediate filaments
Membrane Structure and FunctionCollagen
proteoglycan
Fibronectin
Hydrophilic vs Hydrophobic
Membrane Structure and Function (con’t)
Fluid Mosaic Model•The Fluid Quality of Membranes + held together by hydrophobic interactions - lipids/proteins drift about laterally
+ unsaturated hydrocarbon tails - maintain fluidity at low temperatures
+ cholesterol- stabilizes the membrane
• restrains movement at high temp.• hinders close packing at low temp.
Membrane Structure and Function (con’t)
Fluid Mosaic Model• Membranes as Mosaics + membrane is collage of proteins
- integral proteins• transmembrane
- peripheral proteins• appendages
Membrane Structure and Function (con’t)
Functions of Membrane Proteins• Transport
• Enzymatic Activity
• Signal Transduction
• Intercellular joining
• Cell-cell recognition
• Attachment to the cytoskeleton and ECM
Signal Transduction with G proteins
Voltage Gated Ion Channels
Diffusion
• A.K.A. simple diffusion
• Movement of small molecules across a selectively permeable membrane from an area of HIGH concentration to an area of LOW concentration w/o the use of energy (DOWN the concentration gradient)
e.g. O2, CO2, urea, & alcohol
Traffic Across Membranes (con’t)
Passive Transport• Osmosis + the diffusion of water
- hypotonic,hypertonic, isotonic
Tonicity – the ability of a solution to cause a cell to gain or lose water
Osmoregulation – the control of water balance e.g. contractile vacuole in paramecium
Osmosis The diffusion of WATER across a selectively
permeable membrane
OSMOTIC PRESSURE
The pressure exerted on plasma membranes in solution• Isotonic solution• Hypertonic solution• Hypotonic solution
Water Potential
• The physical property predicting the direction in which water will flow, controlled by the solute concentration
Water potential (ψ) = pressure potential (ψp ) + solute potential (ψs )
Plasmolysis
A phenomenon in plant cells in which the cytoplasm shrivels and the plasma membrane pulls away from the cell wall when the cell loses water to a hypertonic environment.
Osmotic Potential
The tendency of water to move across a selectively permeable membrane into a solution
Determined by measuring the pressure required to stop the osmotic movement of water into the solution.
Traffic Across Membranes (con’t)
Passive Transport• Facilitated Diffusion + diffusion with the help of transport proteins
- gated channels
Facilitated DiffusionProtein Channel or Pore
Facilitated DiffusionProtein Carrier
Traffic Across Membranes (con’t)
Active Transport• energy-requiring process + ATP • pumps molecules against concentration gradient + Na+/K+ pump
Active Transport
• Requires cell energy (ATP) to move molecules AGAINST the concentration gradient; from an area of LOW concentration to an area of HIGH concentration
• Sodium–Potassium pump (Exchange 3 sodium ions for 2 potassium ions)
• Hydrogen ion, or proton pump (Pump hydrogen ion against the concentration gradient)
Phosphorylation
The addition of a phosphate (PO4) group
(From ATP) to a protein or a small molecule
This changes the protein shape
Active Transport (Uniport)
Active Transport Na-K Pump
Na-K Pump Antiport
Traffic Across Membranes (con’t)
Membrane Potential• electrogenic pump + proton pumps (H+)• electrochemical gradient + cotransport
Traffic Across Membranes (con’t)
Bulk Media Transport
• Endocytosis – Vesicle is created from the invagination of the plasma membrane, which pinches off, bringing large molecules into the cell
• Pinocytosis – Cell drinking (endocytosis)
• Phagocytosis – Cell eating (endocytosis)
• Receptor Mediated Endocytosis – Substrate binds to receptor found on the plasma membrane to be brought into the cell
• Exocytosis – Vesicle binds to the plasma membrane releasing the contents outside of the cell
Traffic Across Membranes (con’t)
Transport of Large Molecules• Exocytosis + the cell exports macromolecules using vesicles from Golgi apparatus• Endocytosis + the cell takes in macromolecules by forming new vesicles from membrane
- phagocytosis (“cellular eating”)- pinocytosis (“cellular drinking”)- receptor-mediated endocytosis
+ ligands
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