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

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 Cytoskeleto

n

Microvilli

• Increase surface area for absorption• Attach to cytoskeleton

Centrioles

Cilia

Fig. 03.19

Ribosomes

Endoplasmic reticulum

Golgi apparatu

s

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 Reactionsglucose + oxygen + ADP carbon dioxide + water + ATP

• Glycolysis: – glucose to pyruvic acid (in cytosol)

• Tricarboxylic acid cycle (TCA cycle):– pyruvic acid to CO2 (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 codonscode 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 2nd 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. 03.09

Gated ion channels control permeability

Fig. 03.10

Facilitated diffusion:

it’s passive and

controls permeabilit

y

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-Potassiu

m Exchange Pump

Fig. 03.11

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. 03.13

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. 03.31

DNA Replication

• DNA strands unwind • DNA polymerase attaches

complementary nucleotides

Fig. 03.32

DNA is replicated in a semiconservati

ve 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

&Cytokinesi

s

Fig. 03.33

Chemicals Controlling Cell Division

Cancer

Fig. 03.34

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