The Cell & Mitosis

The Cell: Fundamental Unit of Life Life as we define it consists of cells All cells arise from previously existing cells Organisms depend upon the activity of cells to exist Subcellular structures are responsible for specific cellular biochemical functions according to the “complimentarity of structure & function” Rudolf Virchow says:

This is Modern Cell Theory! There are TRILLIONS of cells in your body Approximately 200 distinct types They range in size from about 2 micrometers (sperm) to over a meter (motor neurons)

Anatomy of a Typical Animal Cell

Organelle Functions

The Plasma Membrane

Functions of membrane proteins

More functions of membrane proteins

Subcellular organelles and other subcellular structures Cytosol – the fluid portion of the cytoplasm Cytoplasm – cytosol + subcellular organelles Many organelles are bound by their own phospholipid membranes All have their own unique functions

The Cytoskeleton

Microvilli Increase surface area for absorption Attach to cytoskeleton

Centrioles

Cilia

Fig Ribosomes

Endoplasmic reticulum

Golgi apparatus

Transport Vesicles Figure 3–7a Carry materials to and from Golgi apparatus

Lysosomes

Mitochondria: Powerhouse of the Cell

Mitochondrial Function Mitochondrion takes chemical energy from food (glucose): –produces energy molecule ATP

The Reactions glucose + oxygen + ADP  carbon dioxide + water + ATP Glycolysis: –glucose to pyruvic acid (in cytosol) Tricarboxylic acid cycle (TCA cycle): – pyruvic acid to CO 2 (in matrix) The TCA cycle is more commonly known as “Krebs Cycle” or the Citric acid cycle

The Nucleus

Structure of the Nucleus Nucleus: –largest organelle Nuclear envelope: –double membrane around the nucleus Perinuclear space: –between 2 layers of nuclear envelope Nuclear pores: –communication passages

DNA: Blueprint of Life

Protein Synthesis Transcription: –copies instructions from DNA to mRNA (in nucleus) Translation: –ribosome reads code from mRNA (in cytoplasm) –assembles amino acids into polypeptide chain

To produce a protein the DNA must be “transcribed” into mRNA

Translation mRNA moves: –from the nucleus –through a nuclear pore Figure 3–13

Translation (2) mRNA moves: –to a ribosome in cytoplasm –surrounded by amino acids

Translation (3) mRNA binds to ribosomal subunits tRNA delivers amino acids to mRNA

Translation (4) tRNA anticodon binds to mRNA codon 1 mRNA codon translates to 1 amino acid

Translation (5) Enzymes join amino acids with peptide bonds Polypeptide chain has specific sequence of amino acids

Translation (6) At stop codon, components separate

Translation summary

3 letter “words” called codons code for amino acids

Summary of protein synthesis

Membrane permeability An important function of the membrane is to control what can enter or leave the cell How easily something passes through is called “permeability” If something cannot pass through the membrane is said to be “impermeable”

Gradients The differential concentrations of substances leads to the establishment of gradients According to the 2 nd LTD, things tend to move from a high concentration to a low concentration. If there is a gradient across a membrane, particles will want to flow across that membrane

Gradients can be of concentrations solutes or charged particles such as ions. Ion gradients are called electrical gradients

Types of transport Passive –Simple diffusion –Facilitated or protein mediated –Filtration –Osmosis Active –ATP driven solute pumps –Vesicular Endocytosis –Phagocytosis –Bulk-phase endocytocysis (pinocytosis) Exocytosis

Cell transport mechanisms

Diffusion and the Cell Membrane Diffusion can be simple or channel-mediated

Simple Diffusion Materials which diffuse through cell membrane: –lipid-soluble compounds (alcohols, fatty acids, and steroids) –dissolved gases (oxygen and carbon dioxide)

Channel-Mediated Diffusion Materials which pass through transmembrane proteins (channels): –are water soluble compounds –are ions

Facilitated Diffusion Passive Carrier mediated

Fig Gated ion channels control permeability

Fig Facilitated diffusion: it’s passive and controls permeability

Diffusion rate influences Slope of concentration gradient Temperature Molecular or atomic weight of solute Density of solvent Surface area Diffusion distance

Factors in Channel-Mediated Diffusion Passage depends on: –size –charge –interaction with the channel

Osmosis Osmosis is the diffusion of water across the cell membrane

Tonicity Isotonic – same concentration of solute inside of the cell as outside. No net movement of water Hypotonic – lower concentration of solute outside than in. Water move into cell (causes lysis). Hypertonic – higher concentration of solute outside of cell than inside. Watre moves out of cell (causes crenation).

Effect of tonicity on red blood cells

Active Transport It requires expenditure of cellular energy Usually involves ATP Can be primary or secondary Includes pumps & bulk phase or vesicular mechanisms

Sodium- Potassium Exchange Pump

Fig The sodium/potassium pump: an antiport system

Secondary Active Transport Na + concentration gradient drives glucose transport ATP energy pumps Na + back out

Vesicular transport Endocytosis – taking things in. –Receptor mediated –Phagocytosis –Pinocytosis Exocytosis – secreting things.

Fig Receptor mediated endocytosis

Pinocytosis: cellular drinking

Phagocytosis Phagocytosis (cell eating) –pseudopodia (psuedo = false, podia = feet) –engulf large objects in phagosomes

Exocytosis Ejects secretory products and wastes

Electrical Charge Inside cell membrane is slightly negative, outside is slightly positive Unequal charge across the cell membrane is transmembrane potential Resting potential ranges from —10 mV to —100 mV, depending on cell type

Mitosis Every cell in your body arises from the process of mitosis Before a cell can reproduce itself, it must first replicate its DNA

Fig

DNA Replication DNA strands unwind DNA polymerase attaches complementary nucleotides

Fig DNA is replicated in a semiconservative pattern

Then the cell goes through the following stages Prophase Metaphase Anaphase Telophase Cytokinesis

Prophase

Late prophase

Metaphase

Anaphase

Telophase: defined by the presence of a cleavage furrow & Cytokinesis

Fig

Chemicals Controlling Cell Division

Cancer

Fig Cells can be highly specialized. The structural specializations reflect their function!

SUMMARY (1 of 4) Structures and functions of human cells Structures and functions of membranous and nonmembranous organelles

SUMMARY (2 of 4) ATP, mitochondria, and the process of aerobic cellular respiration Structures and functions of the nucleus: –control functions of nucleic acids –structures and replication of DNA –DNA and RNA in protein synthesis

SUMMARY (3 of 4) Structures and chemical activities of the cell membrane: –diffusion and osmosis –active transport proteins –vesicles in endocytosis and exocytosis –electrical properties of plasma membrane

SUMMARY (4 of 4) Stages and processes of cell division: –DNA replication –mitosis –cytokinesis Links between cell division, energy use, and cancer

Next, Tissues