Cell Physiology

• The Cellular Environment– Body Fluids• Composed primarily of water• Intracellular fluid- fluid found inside cell. • Extracellular fluid- fluid outside cell.• Interstitial fluid- fluid contained within the tissue,

except for blood found within lymph and blood vessels.

Ions, Electrolytes, and pH

• What are ions?– Cations– Anions– Electrolytes

• In sick or injured animals, electrolyte concentrations and pH of intracellular and extracellular fluid can become abnormally high or low

• Review ions from chapter 2..

Membrane Processes: Excretion and Absorption

• Tissue fluids are also loaded with fatty acids, amino acids, hormones and dissolved gases.

• In order to maintain homeostasis cell must select what it needs from extracellular fluid and bring it into intracellular environment.

• Must excrete waste products or transport resources needed in other parts of the body to the extracellular compartment.

• Processes may be passive (do not require ATP) or active (do use ATP).

Cell membrane may be impermeable to some substances and freely permeable to others. It may also be selectively permeable, allowing some molecules through but not others.

Passive Transport Processes

• Remember: No Energy Required!• 4 Passive Processes:– Diffusion– Facilitated Diffusion– Osmosis– Filtration

Diffusion• Kinetic movement of molecules from higher to lower concentration via

concentration gradient- the difference between the concentration of one area and the concentration of another.

• Will continue until the molecule is evenly dispersed throughout the solution

• Determining factors for Diffusion thru a membrane:1. Molecular size – small can move through2. Lipid solubility – lipids can pass lipid bilayer3. Molecular charge – ions move through special channel proteins4. Temperature – faster in hot solution

The spectrum between the most concentrated and least concentrated area is called the concentration gradient.

As molecules move from high concentration to low, they are said to be moving down the concentration gradient, defusion can be defined as moving down the concentration gradient.

Facilitated Diffusion

• Selective carrier proteins assist in movement of molecules from higher to lower concentration; speed of diffusion is limited by saturation of carrier molecules.

Simply put the molecule needs assistance to pass through the membrane. This takes no energy on the part of the cell.

• http://www.wisc-online.com/objects/ViewObject.aspx?ID=AP11103

Osmosis

• Passive movement of water through a semipermeable membrane from dilute solution to more concentrated one.

• Opposite of diffusion as water, not solute is moving. Also requires semipermeable membrane.

If the concentration is the same inside and outside of the cell, it’s called isotonic.

If the extracellular fluid is hypotonic, the inside of the cell is more concentrated than the outside.

If the extracellular fluid is hypertonic, then the outside is more concentrated than the outside.

The difference between the pressure of blood and interstitial fluid or lymph is called oncotic pressure. This is important in maintaining fluid balance between blood and surrounding tissues.

Filtration

• Hydrostatic pressure (caused by the beating heart) forces liquid and small molecules through a membrane.

• Liquids pushed through a membrane when the pressure on one side is greater than that on the other side.

• An example is the blood pressure, or coffee through the filter of a coffee maker.

Active membrane process:

When the cell is required to use energy. Some molecules can’t enter the cell with passive routes because…•They are not lipid soluble•They are too large•They are on the wrong side of the concentration gradient.

They can move in or out of the cell by either active transport or cytosis

Active Transport Processes• Remember: Requires Energy (ATP)!• Relies on a carrier protein with a specific binding site• Does not require a concentration gradient• Symport system – substances are moving in the same direction• Antiport system – substances are moved in opposite directions• Include:

– Active Transport– Endocytosis

• Phagocytosis• Pinocytosis• Receptor mediated

– Exocytosis

Active Transport

• Active movement of molecules by specific carrier protein; molecules may move against concentration gradient.

Endocytosis:Enables large particles, liquid substances and even entire cells to be taken into a cell by engulfing.

If the cell engulfs solid material, it’s called phagocytosis

Endocytosis

• Phagocytosis– Cells engulf solid substances

• Pinocytosis– Cells engulf liquid substances

• Receptor mediated– Specialized protein receptors bind to ligands

specific receptors.• Ligand-small molecules that bond to larger chemical

groups or molecules.

Exocytosis

• Excretion of waste products and secretion of manufactured substances.

• Packaged in secretory vesicles which fuse with cell membrane and are ejected to extracellular space.

Life Cycle of the Cell

• Two types of division of cells.• Meiosis- Reduction division– Found in reproductive cells. End up with half of

what start with.• Mitosis- exact replication of cell.

• We will focus mainly on Mitosis for this chapter.

Mitosis• Life cycle has been divided into two major periods:

– Interphase• When cell is growing, maturing, and differentiating.• Cells spend majority of time in this phase.

Interphase

• Period between cell divisions.• Originally thought to be a resting phase, but

the cell is carrying out it’s normal life, so this is called the metabolic phase.

• Nucleus and nucleoli are visible and chromatin is arranged loosely throughout the nucleus.

DNA Replication• Many cells are continually replicating to maintain body tissues, to

heal wounds, or to enable growth• DNA must be replicated before the cell can divide – a copy of DNA is

made to be passed to the daughter cell• Occurs during Interphase

DNA Replication• Process:

– Enzymes called DNA helicases pull apart the parental DNA double helix so the bases no longer form base pairs

– Next, enzymes called DNA polymerases move along each separated parental DNA strand and match each base on the strand with free nucleotides that have a complimentary base (an A is matched with a T)

– Then, DNA polymerase connects the free nucleotides together to form new DNA strands

– When replication is complete, the parental strand and the new strand wind together to form a double helix

– The lead strand, is made continuously; the second (lagging) strand is made in segments, and

– DNA ligase joins the segments– The identical DNA strands become chromatids, joined together at the

centromere to form a chromosome

Divided into three subphases:Growth 1 (G1)- metabolic activity and cell growth; time variable (min-yrs) depending on cell type. The cell doubles in size and the number of organelles also double.

Synthetic (S)- DNA replication

Growth 2 (G2)- very brief; synthesis of enzymes and proteins needed for mitosis

Lead and Lagging Strands

Mitotic PhaseWhen cell is actively dividing.Composed of:

ProphaseMetaphaseAnaphaseTelophase

Mitotic Phase- Cell Division

• Cytokinesis- division of the cytoplasm.

• Prophase– Chromatin coils and are composed

of two identical chromatids – Spindle apparatus appears– Normal synthetic processes cease.– Nuclear envelope disintegrates

• Metaphase– Chromosomes are lined up

in center of spindle.– Centromere of each

chromosome is attached to a spindle fiber.

• Anaphase– Centromeres split apart and each chromatid

becomes its own chromosome.– Spindle fiber separates, and chromosomes are

pulled away from each other.– Cytoplasm constricts along metaphase plate.

• Telophase– Final stage of mitosis– When chromosomal movement stops– Chromosomes reach poles and begin to unravel.– New nuclear envelope appears as well nucleoli.– Cytokinesis ends telophase.– New daughter cells enter interphase.

Control of Cell Division

• Some cells divide rapidly others not so fast.– Examples of each

• Normal cells stop dividing when they come into contact with surrounding cells. – Called Contact inhibition

• Division can be controlled once numbers reach a certain point.

• Proteins can also allow cells to enter mitotic phase

Protein Synthesis• Protein synthesis is essential for life.• Begins in nucleus• tRNA transcribes DNA information

– Transcription-Genetic information in DNA is copied onto messenger RNA (mRNA)

– Codon- series of 3 RNA nucleotides.• mRNA sends information to cytoplasm

– Translation- Ribosomes bind to mRNA strand (rRNA).– New protein building as codes are translated from nucleotides

to amino acids

Genetic Mutations• A genetic error.• Mutations may be so severe that cell dies, but may also cause no issues

whatsoever.• Some can be repaired by repair enzymes.• May occur spontaneously or due to mutagens.

– Viruses– Ionizing radiation– Certain chemicals

– What is cancer?– What is chemotherapy?

Cell Differentiation and Development

• Differentiation- The progressive acquisition of individual characteristics by cells to enable them to perform different functions.

• Differentiation is important as it keeps cells focused on a particular function.

• http://www.youtube.com/watch?v=dA5RfoGiupM

• http://www.youtube.com/watch?v=y8gZCTjAbVs&feature=related