the cell & mitosis. the cell: fundamental unit of life life as we define it consists of cells...
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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