Biology Chapter 4 Cell Structure And Function

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Cell Theory

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- All organisms are composed of cells

- Cells come only from preexisting cells because cells are self-reproducing

- Cells are the basic units of structure and function in organisms

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Matthais Schleiden

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- German biologist botanist who studied cells (1830s)

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Theodor Schwann

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- German biologist zoologist who studied cells in the 1830s

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Unifying concept in biology

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Everything is made up of cells

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Rudolp Virchow

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- German physician

- Cells come only from preexisting cells because cells are self-reproducing

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Cell Size

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Range in size from 1 mm down to 1 um (micrometer) in diameter)

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Cells need a large surface area of plasma membrane because?

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To adequately exchange materials

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What requires cells to be small?

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- Surface area to volume ratio

- Decreases the efficiency of transporting materials in and out of the cell

- Advantageous for exchanging molecules

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Compound Light Microscope

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- Light is passed through the specimen

- Focused by a series of glass lenses

- Forms an image on the human retina

- Maximum magnification about 1000x

- Resolves objects separated by 0.2 um, (500x better than human eye which is 1.0)

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Transmission Electron Microscope

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- Abbreviated T.E.M

- Electrons passed through specimen and are focused by a set of magnetic lenses

- Image is formed on a fluorescent screen similar to a TV screen then photographed

- Provides greater magnification than compound

- Resolves objects separated by 0.0002 um, 100,000x better than human eye

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What is the microscope that provides an internal view of a specimen?

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Transmission Electron Microscope

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Scanning Electron Microscope

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- Abbreviated S.E.M

- Specimen is sprayed with thin coat of metal

- Then an electron beam is scanned across the surface of the specimen and the surface metal emits secondary electrons

- Emitted electrons are detected and focused by magnetic lenses

- 3D image is formed on screen then photographed

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Which microscope provides an external 3D view?

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Scanning electron microscope

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Magnification

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Ratio between the size of an image and its actual size

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Resolution

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Minimum distance between two objects that allows them to be seen as two separate objects

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Contrast

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Difference in shading of an object compared to its background

(Uses: Fluorescently tagged antibody molecules can help visualize subcellular components like specific proteins)

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Difference between light rays and electrons?

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Light rays can be bent (refracted) and focused as they pass through glass, but electrons cant

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Electrons

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Have a charge and can be focused by electromagnetic lenses

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Viewing and Recording of Electrons

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- Use electromagnetic lenses to direct electrons leaving the specimen to a screen or photographic plate, making it viewable to the human eye

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Confocal Microscopy

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- Narrow laser beam is scanned across a transparent specimen

- Beam is focused on one very thing plane in the cell

- Microscopist can "optionally section" a specimen by focusing up and down

- Sections are made at different levels
- Allows assembly of 3D electronic image that can be displayed and rotated

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Prokaryotic Cells

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- Lack membrane bound nucleus

- Structurally smaller and simpler than eukaryotic cells (which have a nucleus)

- 2 Taxonomic domans: Bacteria and Archae

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The 2 Domains of Prokaryotic Cells

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Bacteria

Archaea

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Domain Bacteria

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- Cause disease (1 out of 50,000) but are also environmentally important as decomposers

- Can be useful in manufacturing products and drugs

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Domain Archaea

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- Live in extreme habitats similar to primitive earth

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Prokaryotics domains are structurally similar but?

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Biochemically different

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Structure of Prokaryote

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- Extremely small (1-1.5um wide and 2-6 um)

- 3 Basic Shapes (Spherical coccus, rod-shaped bacillus, spiral spirillum if rigid or spirochete if flexible)

- Cell envelope includes plasma membrane, cell wall, glyococalyx

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3 Shapes of Prokaryotes

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Spherical coccus

Rod shaped bacillus

Spiral spirillum (if rigid) or spirochete (if flexible)

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Plasma membrane

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Lipid Bilayer with embedded and peripheral proteins

- Form internal pouches (mesosomes) that increase surface area

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Cell Wall

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Maintains shape of the cell and strengthened by peptidoglycan

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Glycocalyx

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Layer of polysaccharides on outside of cell wall

- Well organized and resistant to removal (capsule)

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Structure of Prokaryotes include

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- Ribosome

- Flagellum

- Fimbriae

- Nucleoid

- Plasma membrane

- cell wall-capsule

- cytoplasm

- plasmids

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Nucleoid

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Region that contains the circular DNA molecule

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Ribosomes

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Tiny structures in the cytoplasm that synthesize proteins

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Conjugation pili

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Rigid tubular structures used to pass DNA from cell to cell

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Cytoplasm

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- Semifluid solution encased by plasma membrane which contains water, inorganic and organic molecules, enzymes

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Eukaryotic Cells

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Cells that contain

- Membrane bound nucleus that houses DNA

- Have specialized organelles

- Plasma membrane phospholipid bilayer that separates cell contents from environment and regulates passage of materials in and out

- Larger and compartmentalized

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Origin of the Eukaryotic Cell

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- Fossil Records suggest first cells were prokaryotes

- Eukaryotes are more related to archaea than bacteria

- Nucleus is believed to evolve by invagination of plasma membrane (which also explains origins of endoplasmic reticulum and Golgi)

- Energy organelles (such as mitochondria - humans and chloroplasts - plants) may have come from eukaryotic cells engulfing smaller prokaryotic cells

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Energy organelles of Eukaryotic cells

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- Such as mitochondria and chloroplasts

- May have originated when cell engulfed smaller prokaryotic cells

- Endosymbiotic theory is the name of the hypothesis

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2 Classes of Organelles

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Endomembrane System

Energy Related Organelles

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Endomembrane System (Organelle)

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Organelles that communicate with one another via membrane channels or small vesicles

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Energy related organelles

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Such as Mitochondria and chloroplasts, they are independent and self sufficient

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Eukaryotic Cells

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- Cell is a system of interconnected organelles that work together.

- Outside of the nucleus, focuses on transporting and communication.

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Nucleus

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Command center of cell, usually in center

- Separated from cytoplasm by nuclear envelope

- Phospholipid bilayer

- Nuclear pores permit exchange between nucleoplasm and cytoplasm

- Contains chromatin in nuceloplasm

- Nucleolus composed of rRNA

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Chromosomes

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- Condensed form of chromatin (which contains nucleic acids and proteins)

- Formed during cell division

- Carriers of genetic information

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Ribosomes

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-Composed of rRNA

- Located on ER rough, free in cytoplasm, or in groups called polyribosomes

- Site of protein synthesis in cell

- Significant in DNA transcription and translation

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Process of transcription and translation

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-Information for gene is copied into mRNA, exported into cytoplasm

- Ribosomes receive mRNA with coded message about DNA and correct amino acid sequence for protein synthesis

- Proteins synthesized by cytoplasmic ribosomes stay in cytoplasm, those made by ER end up in ER

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Central dogma of molecular biology

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DNA to mRNA to protein (sequence of events)

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Endomembrane System

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- Series of intracellular membranes that compartmentalize cell

- Restrict enzymatic reactions to specific compartments within cell

- Consist of nuclear envelope, membranes of ER, golgi apparatus, Vesicles

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Endoplasmic Reticulum

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- System of membrane channels and saccules continuous with outer wall of nuclear envelope

- Two types: Rough and Smooth

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Rough ER

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- Studded with ribosomes on cytoplasmic side

- Synthesizes proteins

- Modifies and processes proteins
- Form transport vesicles which can move to Golgi apparatus

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Smooth ER

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- No ribosomes

- synthesis of lipids

- sites of various synthetic processes, detoxification and storage

- forms transport vesicles (move to golgi)

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Where does insulin come from?

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Comes from pancreas

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Diabetes

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If pancreas does not produce enough insulin

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Golgi Appartus

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- Modifies proteins and lipids with "signal" sequences (Receives vesicles from ER on cis face, then after modification, packages proteins and lipids in vesicles to leave Golgi from trans face

- Some go within cell, out of cell, or return to ER

- Analogous to the post office

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Lysosomes

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- Membrane bound vesicles (not in plants)

- Produced by Golgi apparatus

- Contains powerful digestive enzymes and highly acidic (Digest large molecules to small, recycle cellular resources)

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Lysosomal storage diseases

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- Caused by defect in lysosomal enzyme

Ex: Tay Sachs

Ex: Gene therapy restores missing enzymes to cells

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Endomembrane System Summary

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- Proteins made in rough ER and lipids from smooth ER transported in vesicles to Golgi

- Golgi modifies, sorts, packages into vesicles for various destinations

- Secretory vesicles carry products to membrane where exocytosis produce secretions

- Lysosomes fuse with incoming vesicles and digest macromolecules

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Endomembrane exocytosis Examples

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-Mammary glands produce milk

-Pancreas produces digestive enzymes

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Microbodies

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Contain specialized enzymes to perform special metabolic functions

(ex: peroxisomes)

- Similar to lysosomes (membrane bound vesicles, enclose enzymes, lack of peroxisomal membrane protein results in ALD - neurological damage, active in lipid metabolism, catalyze reactions that produce Hydrogen Peroxide

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Vacuoles

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Membranous sacs larger than vesicles

- Store materials that occur in excess

- Some very specialized (ex) contractile

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Plant cells typically have a

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Central vacuole

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Central vacuole (in Plant cells)

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- up to 90% of some plant cells

- Functions: (storage of water, nutrients, pigments and waste products; development of turgor pressure; toxic substances used for protection from herbivoes; some functions performed by lysosomes in other eukaryotes)

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Chloroplasts

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- Energy producing

-Double membrane

-Inner membrane infolded that form d isclike thylakoids, stacked to form grana and suspended in semifluid stroma

- green due to chlorophyll (green photosynthetic pigment) and found ONLY in inner membranes of chloroplast

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chloroplasts

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- type of plastid (membranous organelles) serve as sites of photo synthesis

- Capture light energy to drive cellular machinery

- photo synthesis (solar energy + CO2 + H2O -> Carbohydrates + Oxygen)

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Mitochondria

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- contained by nearly all eukaryotic cells, plant, algae and animal cells

- smaller than chloroplast

- numbers vary by activity

- contain ribosomes and own DNA

- double membrane

- cellular respiration

- produce most ATP used by cell

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Double membrane of mitochondria

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- inner membrane surrounds matrix and is convoluted (folded inward) to form cristae

- matrix: inner semifluid substance containing respiratory enzymes

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cytoskeleton

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- maintains cell shape

- assists movement of cell/organelles

- internal transport

- 3 types of macromolecular fibers (actin, intermediate filaments, microtubules)

- assemble/dissemble

- comparable to bone/muscle in animal

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actin filaments

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- dense web under plasma membrane and maintain cell shape

- support for microvilli in intestinal cells

functions:

- intracellular traffic control

- component in muscle contraction

- important in animal cell division

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intermediate filaments

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- intermediate in size between actin and microtubules

- vary in nature from tissue to tissue

- function: support nuclear envelope, cell-cell junctions like those holding skin cells tightly together, protein keratin provide mechanical strength to skin cells

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microtubules

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functions:
- interact with 'motor' molecules to cause movement of organelles within cell

- mitotic spindle distribute chromosomes during cell division

- replication of cells

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centrioles

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- made out of microtubules

- located in centrosome of animal cells

- VERY IMPORTANT IN CELL DIVISION

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cilia

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- hairlike and small

- help in cell movement

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flagella

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- "long tail" typically

- aid in movement

- ex: sperm cells

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Distinctive Features of Organelles

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mitochondria: animal and plant

chloroplast: plant (photosynthesis)

lysosome: animal

flagella: aid in movement, get something away, suck something in

cilia: sensory (ex: lungs, digestive tract)

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Structure of Eukaryotic Cell

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- Production of specific molecules take place in or on organelles by enzymes

- Products are transported around cell by vesicles

- Cell Walls contain cellulose (In plant cells, fungi, protists)