The cell

Lecture Notes

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I. Human Cell Structures/Function
Check out this link on comparative sizes of cells, cell structures, molecules and elements (slide the scale)

A. Plasma membrane structure
1. Bilayer of phospholipids
 very fluid layer allowing membrane associated molecules to float within membrane.
phospholipid molecules have both polar and non-polar regions -nonpolar part will turn from H2O inside (cytosol) and outside (extracellular fluid), polar part will orient always turn towards water  so membrane will seal to itself.

 lipid-based molecules can pass through because they dissolve in non-polar part

H2O, CO2 and O2 can pass because they are so small

larger and water soluble (polar) molecules cannot move through easily because they do not dissolve in non-polar part

charged ions cannot pass because charges are repelled.

2. Cholesterol - maintains membrane integrity at all temperatures, flexible yet strong.

3. Proteins (on surface and embedded)

a. Act to allow transport of water soluble substances and water through membrane protein pores (including gated channels and transporters) and protein pumps

b. receptors for hormones and neurotransmitters allowing communication between cells.

c. Markers for cell identification (self vs. not self for immunity purposes) proteins are on surface

d. Cell connection proteins make it so cells can adhere to each other and form tissues.

e. Enzymes on membrane surfaces create/alter chemicals inside cell
Diagram and label cell membrane components-list the functions of each component.

B. Functions of membrane *Membrane function concept map
1. Membrane transport -provided by variety of membrane proteins (pores, gated channels, pumps)

 cell membrane controls flow rate of molecules into and out of cell to extracellular fluid around it
(allows some molecules in and not others) therefore selectively permeable membrane

a. Passive methods (no ATP, molecule concentration gradient is driving force for movement)

1) Simple diffusion movement of molecule along concentration gradient.
Ex. O2, CO2, lipids (steroid hormones, fatty acids, glycerol) through bilayer,
Ex. ions through pores or gated channel proteins

2) Osmosis - water flows towards area of highest number of dissolved molecules(= highest osmotic pressure)
Ex. H2O through membrane bilayer and transport pore proteins

3) Channel-mediated facilitated diffusion- substance combines with membrane protein channel allowing the substance to move down its gradient. Most common channels are gated ion channels, for ions like Na and K

4) Carrier-mediated facilitated diffusion- substance combine with membrane protein transporter, which changes shape, allowing the substance to move down its gradient.
glucose and amino acid molecules are transported this way.

b. Active processes (ATP is driving force of transport, movement against molecule's concentration gradient) 1) Active transport - ATP provides energy to cause membrane protein transport pumps to move substance against its concentration gradient. (e.g., Na+/K+ pumps, Na+ pumps, Na+/H+ pumps). Ex. ions, glucose, amino acids

2). Exocytosis - moving substance out into extracellular fluid (e.g.. secretion of hormones, neurotransmitters and digestive enzymes) via vesicles

3) Endocytosis -moving substance into cytosol (e.g.. white blood cells phagocytizing bacteria) via vesicles

List mechanisms for the tranport of: ions (2 mechanisms), glucose, amino acids, water, lipid hormones, gases, bacteria and secreted proteins.

2. Communication
a. Nervous system
        signals travel along surface of neuron and muscle membranes using transport proteins.
        membrane has receptor proteins for neurotransmitter signal chemical to promote signal formation

b. Endocrine system
        membrane has receptor proteins for hormone signal chemical to alter cell function
 

3. Tissue formation-membrane proteins adhere to each other in adjacent cells.
 

4. Identification/recognition-specific proteins allow immune system to recognize your cells to avoid immune attack.

5. Enzymatic reactions-many enzymes are found in cell ( and organelle) membranes which act to make/break new molecules.
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List the function of cell membrane-identify the type of protein that provides that function..

C. Cell cytosol
Structure - semitransparent gel-like water solution
Function - media for transport of dissolved substances, area for chemical reactions (hydrolysis)

D. Organelles
1. Nucleus and nuclear membrane

Structure - membrane bound organelle with pores in nuclear membrane to allow exchange with cytosol
Functions -membrane controls access to genetic material.
Enzymes in nucleus promote DNA production (replication) and RNA production (transcription)2. Endoplasmic reticulum Structure -Extensive system of tubes and sacs that interconnect with nuclear and plasma membrane
which transport  and store  molecules to other sites. Rough endoplasmic reticulum contains ribosomes, smooth ER does not.
Functions -Rough ER- assemble polypeptide (ribosomes) and phospholipid synthesis (embedded enzymes)

Functions - Smooth ER - makes steroid lipid, cholesterol and some carbohydrates (embedded enzymes) . Storage of calcium.

3. Golgi complex  Structure - few, membranous organelle
Functions -accepts vesicles from endoplasmic reticulum to provides final modification of proteins for secretion.
forms lysosomes (=cellular digestive, recycling vesicles) inside cell
forms secretory vesicles ( with cell products) for transport to outside cell4. Mitochondria  Structure -membranous organelle with many enzymes
Functions -provide function  of aerobic cellular respiration ( e.g., where energy carrying fuel molecules are broken down to be used to make ATP)5. Cytoskeleton a. Mitotic spindle - tubules allowing movement of chromosomes during cell division

b. Cilia - movement/locomotion of extracellular products and water

c. Flagella- single whip-like structure moves cell.

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An interesting activity on cell organelles

Draw the components of the cell, including plasma membrane, and describe their functions. 

II. Cell Function
A. Protein synthesis-primary activity of cell (e.g., make enzymes, hormones, antibodies, neurotransmitters, etc)
Pretty cool video simulating the following processes

1. Role of DNA -DNA serves as inherited information molecule used as master template (permanent blueprint) for the production of proteins, especially enzymes.

a. Each enzyme comes from one section of DNA molecule, a gene. The genes, then, code for enzymes that might have the ability to hydrolyze glucose, make cholesterol or transport an ion. As such, cell activity and appearance  is governed by information in genes but information is implemented by enzymes.

b. The process of Transcription (in nucleus) is the conversion of a DNA sequence, the gene, into an information carrying mRNA sequence (also makes transfer RNA and ribosomal RNA)

2. Role of RNA -mRNA is information transfer molecule(=temporary blueprint) allowing information to be moved from nucleus to ribosome.

a The process of Translation (at ribosome in cytoplasm or on RER) is when mRNAstrand is read by ribosome to assemble a polypeptide sequence.

b.tRNA moves amino acids to ribosomes

c. rRNA forms the ribosome
 

3. Modification of polypeptide (processing)
    golgi bodies add sugar groups, cleave off parts of polypeptides to modify them into working globular proteins. Completed proteins are packaged and then can stay in vesicle (lysosomes), move to membrane (membrane proteins) or be secreted outside of cell
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  For the synthesis of proteins, describe, in order, the chemicals made, where they are made, and the name of the process.

B. Cell life cycle
Cells spend a great of time working but at the end of their life they must be replaced. There are discernible phases in a cell's life cycle.

1. Interphase

a. Period of growth and other physiological functions that are cell's responsibily. Cells spend most of their life in this part of the cell life cycle. DNA is available for use as template for protein contruction and production. 1) increase in number of organelles and cytoplasm

2) major activity is to produce enzymes for cell's use and for export.

3) many cells produce/export many other things (hormones, glycogen, cholesterol, antibiotics etc)

b. Period of duplication( = replication) of DNA. If cell is to form two cells from one cell then two sets of DNA must be formed. Start with 23 pairs (46) in normal body cells.1) DNA has uncoiled and unzipped strands

2) Enzymes copy both strands

3) Results of two sets of identical DNA

2. Mitotic phases - smooth process of separating two sets of identical genetic material into two cells to promote growth in number or cells or to replace old, dying cells.a. Prophase  chromosomes condense

 nuclear membrane dissolves

 mitotic spindle forms

b. Metaphase  chromosomes arrange in equitorial linec. Anaphase  chromosomes move to opposite sidesd. Telophase  nuclear membrane reforms

 cell cleaves into two

 Chromosomes diffuse

3. Cytokinesis (separation of cytoplasm occurs)

With both mitosis and cytokinesis the entire cell is duplicated and then divided into two cells, thereby replacing cells (or increasing cell number or count)

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Describe the processes involved in making new cells, in each phase of the cell cycle.
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Professor Thomas M. Lancraft
Human Anatomy and Physiology Courses
at St. Petersburg College
St. Petersburg/Gibbs Campus
1/2007