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The Cell

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Antoni van Leeuwenhoek

– (1632-1723), Dutch, maker of first single lens microscope

– The first to document the structure of RBC & the nature of the circulatory system

– protozoans & bacteria, life cycles of many species of insects.

MICROMETER (µm) = 1/1000

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Types of Microscopes

1. COMPOUND/LIGHT MICROSCOPE

Principle: sunlight (light source)

2. ELECTRON MICROSCOPE

Principle: beam of electrons

a. Transmission (magnification: >/=1Mx)

b. Scanning – 3D image <250,000x

Magnification = extent to which an image is enlarged

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Image under Compound microscope

Scanning EMTransmission EM

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CELL

•Robert Hooke (1665) = studied the cork & other plant materials many small partitions separatingcavities cells.

•Basic structural and functional units of an organism

•Carry out all chemical activities needed to sustain life

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Cell Diversity1. Cells that connect body parts2. Cells that cover and line body organs3. Cells that move organs and body parts4. Cell that stores nutrients5. Cell that fights disease6. Cell that gathers information and

controls body functions7. Cells of reproduction

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3 Main Parts

1. PLASMA MEMBRANE

2. CYTOPLASM

3. NUCLEUS

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1. Plasma Membranesyn: plasmalemma, cell membrane- outer covering of the cell- surrounds each cell separate its contents from external environment- regulates what enters & leaves the cell- allows communication

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Plasma Membranesome, cholesterol and glycolipidsLIPID BILAYER + integral and

peripheral proteinsSELECTIVE PERMEABILITY

◦- water & nonpolar (lipid-soluble) molecules e.g. FA, fat-soluble vit., steroids, O2, CO2

mainly made up of phospholipids and proteins (latter, mainly glycoproteins)

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Plasma MembraneImpermeable to: ions, glucose, a.a.transport assisted by: ion channels,

transportersIntegral proteins act as: receptors,

enzymes, cell identity markers

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Plasma Membrane

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rane

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Definition of Terms

•Intracellular fluid (ICF) – inside body cells i.e. fluid in cytoplasm, 2/3 of body fluid

•Extracellular fluid (ECF) – fluid outside body cells

•Interstitial fluid – the ECF between cells ▫ e.g. plasma (in blood vessels), lymph (in lymphatic vessels)

** materials dissolved in body fluids: gases, nutrients, ions, etc.

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Definition of Terms

• Solute – any material dissolved in a fluid• Solvent – fluid in w/c the solute is dissolved e.g. water• Solution – homogenous mixture of 2 or more components (e.g. air, seawater, alcohol)

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Definition of Terms

• CONCENTRATION – the amount of a solute in a solution• CONCENTRATION GRADIENT – difference in concentration between 2 different areas

– moving down vs. moving up

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Substances move across cellular membranes by:

•PASSIVE PROCESSES – substance moves down its concentration gradient using only its own energy of motion (kinetic energy)• SIMPLE DIFFUSION, OSMOSIS

•ACTIVE PROCESSES – cellular energy (e.g. ATP) is used to push the substance through the membrane against its concentration gradient• ACTIVE TRANSPORT, VESICLES

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Passive Processes

1. DIFFUSION – a substance moves from one place to another due to the substance's kinetic energy

• particles move from a region of higher to lower concentration • endpoint: EQUILIBRIUM – substance is evenly distributed throughout the solution and the concentration gradient disappears • may or may not involve a membrane

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Diffusion

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2 Types of Diffusion

1. SIMPLE DIFFUSION • lipid-soluble substances diffuse through the lipid bilayer e.g. O2, CO2, N, f.a., steroids, vit. ADEK, H2O, urea• used in: exchange of gases, absorption of nutrients, release of wastes

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Simple Diffusion

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2 Types of Diffusion

1. SIMPLE DIFFUSION • Ion channels – allow a specific type of ion to move across the membrane through the channel's pore• e.g. K, Cl, Na, Ca

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2 Types of Diffusion

2. FACILITATED DIFFUSION • an integral membrane protein assists a specific substance across the membrane• substance binds to a specific TRANSPORTER on one side of the membrane --> released on the other side after the transporter undergoes a change in shape• movement along a conc. gradient, NO ATP needed• e.g. glucose, fructose, galactose

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Passive Processes2. OSMOSIS = net movement of water through a selectively permeable membrane

- water moves from an area of higher water to an area of lower water concentration

- or, from an area of lower solute concentration to an area of higher solute concentration

OSMOTIC PRESSURE – depends on the concentration of its solute particles

- the higher the solute conc., the higher the osmotic pressure

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Osmosis

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EFFECT of OSMOSIS in CELLS

ISOTONIC = any solution in w/c cells maintain their normal shape and volume, concentrations of solutes are same on both sides

= tissue fluids, blood plasma, 0.9% NSS, 5% dextrose (glucose)

HYPOTONIC = lower concentration of solutes (higher conc. of H2O) than the cytosol inside the cell = cell swells --> ruptures

HYPERTONIC = higher concentration of solutes (lower conc. of water) than the cytosol inside the cell

= cell shrinks

Effects of Osmosis

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Passive Processes

3. FILTRATION = process by w/c H2O and solutes are forced through a membrane (or capillary wall) by fluid or hydrostatic pressure (pressure gradient)

e.g. filtering capacity of the kidney (e.g. in urine formation)

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Active Processes1. ACTIVE TRANSPORT - cellular energy is used to transport substances across the membrane against a concentration gradient (from an area of low to an area of high concentration), needs ATP

- splitting of ATP changes the shape of a transporter protein (PUMP) --> moves a substance across the membrane against its conc. gradient

- Na, K, H, Ca, I, Cl

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Active Transport

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Active Processes2. TRANSPORT IN VESICLES

- VESICLE – small round sac formed by budding off from an existing membrane

- transport substances, take in and release substances

- requires energy (ATP)

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2 Types of Transport in Vesicles

1. ENDOCYTOSIS – materials move into a cell in a vesicle formed from the plasma membrane - substances are surrounded by a piece of the plasma membrane w/c buds off inside the cell to form a vesicle containing the ingested substances.

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2 Types of Endocytosis

1. PHAGOCYTOSIS – large solid particles (e.g. bacteria, viruses, aged or dead cells), are taken in by the cell

- fuses w/ a lysosome --> break down of material

- e.g. WBCs, macrophages

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2 Types of Endocytosis

2. BULK-PHASE ENDOCYTOSIS (PINOCYTOSIS) – cells take up tiny droplets of ECF

- fuses with a lysosome --> enzymatic breakdown of engulfed solutes

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2 Types of Transport in Vesicles

2. EXOCYTOSIS – results in secretion (release of materials from a cell)a. SECRETORY CELLS – release digestive enzymes, hormones, mucus, etc.b. NERVE CELLS – during release of neurotransmitters

* membrane-enclosed secretory vesicles form inside the cell, fuse w/ the cell membrane, and release contents into the ECF

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Exocytosis

Table. 3.2

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Specializations of the Plasma Membrane

•Microvilli•Membrane junctions

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Membrane Junctions1. TIGHT JUNCTIONS = formed from

fusion of adjacent cell membrane --> impermeable or leak-proof sheets

= keep digestive juices & harmful substances from damaging the organs or getting into the bloodstream

2. DESMOSOMES = anchoring junctions (button-like thickenings), prevent cells under mechanical stress from being pulled apart e.g. skin

3. GAP JUNCTIONS = allows communication e.g. heart, nervous system

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2. Cytoplasm• consists of all cellular contents bet. the cell

membrane and nucleus

• Includes: ▫CYTOSOL (ICF) – fluid portion of the

cytoplasm, 55% of total cell volume, 75-90% H2O, site of chemical reactions

▫ORGANELLES – specialized structures inside cells w/ specific functions

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1. Cytoskeleton•network of 3 different types of protein filaments1. MICROFILAMENTS – thinnest, concentrated at

the periphery --> strength and shape- provides mechanical support and generates movement- anchor cytoskeleton to integral proteins- support for microvilli- intercellular attachment

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1. Cytoskeleton2. INTERMEDIATE FILAMENTS – found in parts

of cells subject to tension (stretching), hold organelles in place, intercellular attachment

3. MICROTUBULES – long, hollow tubes, determines cell shape, movement of organelles w/in the cell, migration of chromosomes during cell division, movement of cilia and flagella

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2. Centrosome• found near the

nucleus• Includes:1. Centrioles (paired) –

composed of microtubules

2. Pericentriolar material – composed of tubulins, organizing centers for growth of the mitotic spindle (role in cell division)

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3. Cilia and Flagella

1. CILIA – short, hairlike projections extending from the surface of the cell• propel fluids across surfaces of cells

2. FLAGELLA - move an entire cell

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4. Ribosomes•Tiny, round, dark

bodies•Actual site of protein

production•high rRNA content

• Free ribosomes• attached to RER

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5. Endoplasmic Reticulum (ER)• network of folded membranes • 2 Types• Rough ER – extends from the nuclear envelope,

studded w/ ribosomes, synthesis of secretory proteins and membrane molecules

• Smooth ER – extends from the RER --> network of membranous tubules, lacks ribosomes, f.a. & steroids (e.g. estrogen, testosterone) are produced, detoxification (e.g. alc, pesticides, carcinogens)

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5. Endoplasmic Reticulum (ER)

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6. Golgi Complex•Stack of flattened membranous sacs•Modify and package proteins

•secretory vesicles•carries proteins and phospholipids to become part of cell membrane•incorporated in lysosomes

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7. Lysosomes•membrane-encosed

vesicles, >/= 60 digestive enzymes

•digestion, recycling•autophagy, autolysis

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8. Peroxisomes•Sacs containing

oxidase enzymes•Use oxygen to

detoxify harmful or poisonous substances (e.g. alcohol, formaldehyde)

•Disarm “free radicals” ▫FR → H2O2→H2O▫liver and kidney cells

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9. Proteasomes• continuous

destruction of unneeded , damaged or faulty proteins

• contain proteases

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10. Mitochondria

•powerhouse of the cell (site of ATP production)

•increased in: muscles, liver, kidneys

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3. Nucleus

•most prominent feature of a cell

•NUCLEAR ENVELOPE – separates the nucleus from the cytoplasm

•NUCLEAR PORES – control movement of substances

•NUCLEOLI – sites of assembly of ribosomes

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3. Nucleus

•GENES – hereditary units• direct cellular activities • arranged along chromosomes

• 46 chromosomes (23/parent)• in a nondividing cell, chromosomes appear as diffuse granular mass --> CHROMATIN

•GENOME – total genetic information carried in a cell or organism •

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Protein Synthesis• DNA found in genes gives

instructions for making proteins1. Transcription – DNA is copied -->

RNA2. Translation – information in RNA

(attached to a ribosome) is translated into a sequence of a.a. --> protein molecule

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Transcription• occurs in the nucleus• genetic info in DNA base triplets is

copied into complementary sequence of CODONS in a strand of RNA (helped by RNA polymerase)

• PROMOTER – sequence of nucleotides in DNA where RNA polymerase attaches to

• TERMINATOR – sequence of nucleotides in DNA where transcription ends

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3 Kinds of RNA

1. Messenger RNA (mRNA) – directs synthesis of a protein

2. Ribosomal RNA (rRNA) – joins w/ ribosomal proteins to make ribosomes

3. Transfer RNA (tRNA) – binds to an a.a. and holds it in place on a ribosome until it becomes part of a protein during translation

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Base pairing

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Translation

• mRNA attaches to ribosomes and directs protein synthesis by converting sequence of nucleotides (CODON) into a specific sequence of a.a. --> PROTEIN

• tRNA contains the triplet of nucleotides called ANTICODON

• Protein synthesis ends when ribosome reaches a STOP CODON

• 15 a.a./second

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Somatic Cell Division•process by which damaged, diseased or

worn out cells are replaced

•process by which cells reproduce themselves

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2 Types of Cell Division1. REPRODUCTIVE CELL DIVISION

(MEIOSIS)- the process that produces gametes

(sperm & oocytes)

2. SOMATIC CELL DIVISION- division of all body cells (except

gametes) --> two identical cells•

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Prerequisite of somatic cell division: DNA Replication

•DNA – building blocks “nucleotides”

▫Deoxyribose sugar▫Phosphate group ▫Nitrogen-containing

base

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• duplication of the DNA sequences that make up the genes and chromosomes --> daughter cells w/ same genes and same number of chromosomes

Prerequisite of somatic cell division: DNA Replication

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DNA Replication

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Cell Cycle

• sequence of changes that a cell undergoes from the time it forms until it duplicates its contents and divides into two cells

• 2 MAJOR PERIODS1. INTERPHASE – cell is not dividing2. MITOTIC PHASE – cell is dividing

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Interphase

• DNA replication occurs• manufactures organelles and cytosolic

components• increased metabolic activity• cell is growing

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Mitotic Phase

• consists of:• MITOSIS – nuclear division• CYTOKINESIS – cytoplasmic division into

2 cells

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Mitosis• PROPHASE = chromatin coil and shorten

chromosomes, bar-like bodies▫Chromosome = 2 strands of chromatids, held together

by a buttonlike body, centromere

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MitosisSTAGES:• METAPHASE – chromosomes cluster and align at the center (metaphase plate)

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MitosisSTAGES:• ANAPHASE – movement of chromosomes toward opposite ends of the cell

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MitosisSTAGES:• TELOPHASE – chromosomes uncoil and become chromatin again, nuclear envelope forms around each chromatin mass

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Cytokinesis

• division of a cell's cytoplasm and organelles• formation of cleavage furrow that extends

around the center of the cell• endpoint: 2 new and separate cells

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