bio chapter 4

cell

basic unit of structure and function in all organisms

4 themes of cell

emergent properties; correlation of structure and function; interactions of organisms within their environment; evolution

Robert hooke

first described cells using a light microscope; coined the term "cell"

light microscope

condenser lens focuses light on specimen; light passing through is refracted (bent) with an objective lens and an ocular lens; image is magnified and inverted

magnification

how much larger an object is made to appear compared to its real size; 1000 times with max resolutions

resolution

minimum distance between 2 points that can still be distinguished as 2 separate points (clarity); max resolution is .2 um

electron microscope

far surpassed the resolving power of the light microscope; uses a bear of electrons; can only view dead specimens; resolution 2 nm

transmission electron microscope (TEM)

aims a beam of electrons at a thin section of specimen electrons transmitted through are focused and image magnified by using electromagnetic lenses to bend the paths of the electrons; used to study internal cell structures

scanning electron microscope (SEM)

useful for studying the surface of a specimen; electron beam scans the surface of a specimen; excites secondary electrons on the sample's surface which are collected and focused on a viewing screen

cytology

study of cell structure

cell fractionation

centrifuging disrupted cells to isolate components of various sizes, densities, and shapes; uses and ultracentrifuge (spins up to 80,000 rpm)

steps of cell fractionation

homogenization of tissue using pistons, blenders, or ultrasound
slow centrifugation of homogenate --> nuclei and other larger particles settle to
bottom of tube forming a pellet

unpelleted fluid (supernatant) decanted into another tube
supernatant centrifuged at a faster speed separating out smaller organelles
supernatant decanted again and centrifuged at higher speed (and so on)

prokaryotic cells

bacteria, archaebacteria; no true nucleus and lacks nuclear envelope; no genetic material in nucleiod region; no membrane bound organelles; 0.1-10um

eukaryotic

protists, fungi, plants, animals; true nucleus and bounded by nuclear envelope; nuclear material in nucleus; cytoplasm (cytosol and membrane bound organelles) 10-100um)

cytoplasm

region between cell membrane and nucleus

cytosol

semi-fluid part of cytoplasm

Lower limit of cell size

determined by the smallest size with enough DNA to program metabolism and enough ribosomes, enzymes, etc. to sustain life

upper limits of cell size

determined by the surface area to volume ratio (as a cell increases in size, its volume grows proportionately more than its surface area); surface area must be large enough for cell volume

plasma membrane

boundary of every cell; selective barrier; allows passage of materials into and out of cells

internal membranes in eukaryotic cells

separate cell into compartments; have unique liquid and protein compositions; may take part in metabolic reactions (many enzymes incorporated into membranes); provide localized environmental conditions necessary for specific metabolic processes isolate reactions

nucleus

membrane-bound organelle in a eukaryotic cell; contains most of the genes that control the entire cell; about 5 um in diameter; enclosed by nuclear envelope

nuclear envelope

double membrane enclosing the nucleus; 2 lipid bilayer membranes separated by a space; contains pores (regulate passage of molecules into and out of nucleus)

nuclear lamina

network of protein filaments on envelopes nuclear side; stabilizes nuclear shape

chromatin

genetic material (complex of DNA and histone proteins); make up chromosomes in eukaryotic cells

chromosomes

long, threadlike group of genes; composed of chromatin; each species has a characteristic number of chromosomes; humans have 46 chromosomes (except sperm and egg cells)

nucleolus

spherical region in nucleus of nondividing cells; may be 2 or more; make ribosomal subunits from rRNA and proteins; subunits pass through pores to cytoplasm where they are assembled

protein synthesis

controlled by nucleus; mRNA transcribed in nucleus from DNA; mRNA passes through pores into cytoplasm then attaches to ribosomes where message is translated into a protein

ribosome

cytoplasmic organelle; site of protein synthesis; consists of RNA and protein; made in nucleolus (in eukaryotic cells); many are found in cells with high rates of protein synthesis; found free in cytoplasm or bound to endoplasmic reticulum

free ribosomes

in cytosol; most proteins made here function in cytosol

bound ribosomes

attached to outside of ER; usually make proteins for membrane inclusion or export; many found in cells specializing in protein excretion (pancreas)

endomembrane system

membranes vary in structure or function; may change in composition, thickness, and behavior; (includes: nuclear envelope; ER; Golgi apparatus; lysosomes; vacuoles; plasma membrane)

vesicles

membrane-enclosed sacs that are pinched off portions of membranes moving from 1 membrane to another

endoplasmic reticulum

membranous network of tubules and sacs (cisternae); most extensive portion of end-membranous system; continuous with external membrane of nuclear envelope

cisternal space

internal lumen of ER; continuous with space between membranes of nuclear envelope

smooth ER

cytoplasmic surface lacks ribosomes

rough ER

cytoplasmic surface studded with ribosomes; continuous with outermembrane of nuclear envelope

functions of smooth ER

participates in synthesis of lipids, phospholipids, & steroids; participates in carbohydrate metabolism; detoxifies drugs and poisons; store calcium ions necessary for muscle contraction

functions of rough ER

manufactures secretory proteins; membrane production

rough ER and protein synthesis

ER ribosomes synthesize secretory proteins; growing polypeptide is threaded through ER membrane into cisternal space; protein folds into its native configuration; if destined to be a glycoprotein, enzymes catalyze the bonding of an oligosaccharide to the protein; transport vesicle containing the protein pinches off from a specialized region of ER
(transitional ER)

glycoproteins

proteins covalently bonded to carbohydrate

oligosaccharide

small polymer of sugar units

transport vesicle

membrane vesicle in transport from 1 part of the cell to another

rough ER and membrane production

membrane proteins produced by Er ribosomes (polypeptide is inserted into rough ER membrane); enzymes within ER membrane synthesize phospholipids from materials in cytosol; proteins and phospholipids are assembled and expand ER membrane; expanded membrane transported as a vesicle to other parts of the cell

Golgi apparatus

organelle made of flattened membranous sacs (cisternae); many transport vesicles leave ER and travel to Golgi; finishes, stores, and ships ER products; has 2 pols: cis face and trans face

cis face

"forming face" of Golgi; accepts transport vesicles from nearby transitional ER; vesicle fuses its membrane with the membrane of the cis face and empties its contents into Golgi cisternal space

trans face

"maturing face" of Golgi; vesicles pinch off from Golgi here to transport molecules to other sites

Golgi

enzymes in cisternae modify ER products as they move from cis to trans face; each cisternal has unique enzymes products move from cisternal to cisternal in transport vesicles

Golgi and ER products

alters some membrane phospholipids; alters oligosaccharide portion of glycoproteins; tag some products to be sent to various cell parts (phosphate groups or
oligosaccharides may be added to act as molecular identification tags); sorts products for secretion (these products leave trans face in transport vesicles which
fuse with plasma membrane)

lysosomes

membrane enclosed bag of hydrolytic enzymes; enzymes digest macromolecules; probably pinch off from trans face of Golgi

lysosomal enzymes

lipases, carbohydrases, proteases, nucleases; optimal pH 5; made in RER, processed in Golgi

lysosomal membrane

keeps potentially destructive enzymes separate from cytosol; pumps H++'s inwards to keep optimal pH for enzymes; made in RER processed in Golgi

function of lysosomes

intracellular digestion; recycling of cell parts; programmed cell destruction

intracellular digestion

lysosomes fuse with food-filled vacuoles; hydrolytic enzymes digest food; ex: amoeba eating by phagocytosis; ex: macrophages "eat" bacteria by phagocytosis

phagocytosis

plasma membrane engulfs substances and pinches off to form a particle-containing vacuole

recycling of cell parts

lysosomes engulf other organelles or part of cytosol and digest them; monomers released into cytosol where they can be recycled

programmed cell destruction

important during metamorphosis and development

lysosomal storage diseases

inherited diseases resulting from impaired lysosomal function; lack of specific lysosomal enzymes cause some substances to accumulate--> interferes with cell function

pompe's disease

a carbohydrase that breaks down glycogen is missing; glycogen accumulates and damages liver

tay-sach's disease

a lipase is missing; lipids accumulate in brain

vacuole

membrane enclosed organelle; larger than a vesicle

food vacuole

formed by phagocytosis; site of intracellular digestion in some protists and macrophages

contractile vacuole

pumps excess water from cell; found in some freshwater protozoa

central vacuole

large vacuole found in most mature cell plants; forms when smaller vacuoles from ER and Golgi coalesce; enclosed by tonoplast (part of endomembrane system)

functions of central vacuoles

stores organic compounds (protein storage in seeds, etc.); stores inorganic ions (K+, Cl-); sequesters dangerous metabolic byproducts from cytoplasm; contains pigments in some cells (pigments in flowers); may contain poisonous or unpalatable compounds for protection against predators; absorbs water and elongates cell (promotes plant growth)
contributes to large ratio of membrane surface area to
cytoplasmic volume (only thin layer of cytoplasm
between tonoplast and plasma membrane)

peroxisomes

membrane bound organelles that contain specialized enzymes; found in nearly all eukaryotic cells; form by pinching off from existing peroxisomes; contain peroxide-producing oxidases

functions of peroxisomal reactions

break down of fatty acids into smaller molecules (acetyl coA); detoxification of alcohol and poisons

glyoxysomes

specialized peroxisomes found in germinating seeds; contain enzymes that convert lipids to carbohydrates; make energy stored in seed oils available for the seedling

chloroplasts

chlorophyll-containing plastids; bound by a double membrane; sites of photosynthesis; found in eukaryotic algae, leaves, and other green plant parts; dynamic structures (move, change shape, divide)

chloroplast structure

contain thylakoids (flattened membranous sacs); 3 compartments formed by membranes

thylakoids

membranes contain chlorophyll; take part in initial steps of photosynthesis; some are stacked into grana

intermembrane space

narrow space between the 2 membranes surrounding the chloroplast

thylakoid space

space inside a thylakoid

stroma

space between thylakoids and inner membrane; contains viscous fluid; site of photosynthetic reactions that convert CO2 to sugar

cytoskeleton

network of fibers throughout the cytoplasm; forms a dynamic framework for support, movement, and regulation; supports cell; helps maintain cell shape; enables a cell to change shape; takes part in motility -> interacts with proteins called motor molecules (e. g. organelle movement, muscle contraction, locomotor organelles); takes part in regulation -> transmits signals from cell’s surface to its interior

microtubules (thickest)

found in cytoplasm of all eukaryotic cells

microtubule structure

straight hollow fibers; constructed from a globular protein called tubulin

tubulin

each molecule consists of 2 polypeptide subunits (a-tubulin and B-tubulin); may be disassembled and recycled elsewhere in cell

microtubule functions

cell support and reinforce cell shape; tracks for organelle movement (protein motor molecules interact with microtubules to translocate organelles); separation of chromosomes during cell division

centrioles

pair of cylindrical structures located in the centrosome in animal cells; 9 sets of triplet microtubules arranged in a ring at right angles to each other; replicate during cell division; may organize microtubule assembly during cell division

cilia and flagella

locomotor organelles found in some eukaryotic cells; made of microtubules; propel many eukaryotic unicellular organisms through water; flagella propel motile sperm cells (animals, algae, some plants) cilia draw fluid across the surface of stationary cells (ciliated cells of trachea)

structure of cilia and flagella

extensions of plasma membrane with a core of microtubules; "9+2 pattern;" radical spokes; side arms; basal bodies

9 + 2 pattern

core made of 9 microtubule doublets in a ring around 2 single microtubules in center (doublet = pair of attached microtubules)

radical spokes

connect each doublet to the center

side arms

attach each doublet to neighboring doublet; mace of protein dynein

basal bodies

anchor the micro tubular assembly of cilia and flagella; structurally identical to centrioles (can convert into a centriole or vice versa)

dynein

motor molecule that changes its shape using ATP as energy; shape change and the resistance of the radical spoke causes cilia or flagella to bend

microfilaments

actin filaments

structure of microfilaments

consists of 2 long actin chains wound into a helix; each chain is made of globular protein monomers called G-actin

microfilament functions

provide cellular support; muscle contraction; localized contraction of cells; cytoplasmic streaming in plant cells

intermediate filaments

different in diameter and composition depending on cell type

intermediate filament structure

made of keratin subunits; more permanent than microtubules and microfilaments

intermediate filament functions

bear tension (may serve as framework for cytoskeleton); reinforce cell shape; may fix organelles in place; make up nuclear lamina

cell wall

external to plasma membrane in plant cells; thicker than plasma membrane

cell wall structure

chemical composition differs from cell to cell and species to species; consists of strong cellulose fibers in a matrix of other polysaccharides and proteins

cell wall functions

protects plant cell; maintains cell shape; prevents excess water uptake

plasmodesmata

channels through cell walls connecting cytoplasm of neighboring cells

development of plant cell walls

young cell secretes thin primary cell wall
middle lamella (made of sticky polysaccharides called pectin) between adjacent primary
cell walls -> cements cells together
cell stops growing
cells secretes hardening substances into primary cells wall
secondary cell wall added between plasma membrane and primary cell wall

secondary cell wall

double matrix; supports and protects cell

ECM (extracellular matrix)

meshwork of macromolecules outside plasma membrane; secreted by cells; composed mostly of glycoproteins (mostly collagen); some cells are attached by glycoproteins called fibronectins

collagen

about 1/2 of total protein in vertebrates; forms strong extracellular fibers embedded in a meshwork of glycoproteins called proteoglycans