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