mastering biology chapter 4

cell theory

-all living things are composed of cells
-cells are the basic units of structure & function in living things
-new cells are produced from existing cells

cell

-basic unit of structure and function in living things
-constantly in motion
-all cells contain chromosomes & ribosomes
-the cytoplasm is the interior of all cells
-between 1 & 100 micrometers (µm) in length

Robert Hooke

-used a crude microscope to study a piece of cork
-compared the structures he saw to "little rooms" (cellulae)
-coined the term "cell"

Cellulae

"little rooms"

Antoni van Leeuwenhoek

-discovered bacteria using the microscope
-his reports to the Royal Society of London included drawings & descriptions of his discoveries

Magnification

An increase in the apparent size of an object

micrograph

A photograph taken through a microscope.

resolution

-A measure of the clarity of an image
-The ability to see two objects as separate

light microscope

-Visible light passes through specimen (microorganism/thin slice of animal or plant tissue) through glass lenses
-Lenses bend light so that the image of specimen is magnified as it is projected into eye/camera
-Can effectively magnify objects up to 1,000 times
-Cannot resolve detail finer than 2 micrometers (µm)

electron microscope

-Focuses a beam of electrons through a specimen or onto its surface
-Can distinguish biological structures as small as 2 nanometers (nm)
-Cannot study living specimens, as the methods to prepare the specimen kills the cells

Scanning Electron Microscope (SEM)

-An electron microscope used to study cell surfaces
-Uses an electron beam to scan the surface of a cell, exciting the electrons
-Surface is usually coated by a thin film of gold
-Electrons are detected by a device to translate their pattern onto an image projected onto a video screen
-Produces images that look 3D

Transmission Electron Microscope (TEM)

-An electron microscope used to study cell ultrastructure
-Aims an electron beam through a very thin section of the specimen
-Section is stained w/ atoms of heavy metals
-Electrons are scattered by the more dense parts, creating an image by the pattern of the transmitted electrons
-Electromagnets bend the paths of electrons, magnifying & focusing an image onto a viewing screen/photographic film

cell ultrastructure

cellular anatomy revealed by an electron microscope

surface-to-volume ratio

-Amount of surface area per unit volume
-Smaller cells have a greater SA:V ratio, allowing for greater efficiency in diffusion & transport of nutrients across the cell's surface

cell diffusion

Movement of molecules from an area of higher concentration to an area of lower concentration

plasma membrane

-A thin, flexible boundary between a living cell and its surroundings
-Regulates the flow of material in and out of a cell
-Some proteins form tunnels that shield ions & polar molecules as they pass through the interior

Fusion of a Transport Vesicle (Golgi) w/ the Plasma Membrane

-the contents of the transport vesicle are secreted from the cell
-the membrane of the transport vesicle is added to the plasma membrane

phospholipid bilayer

-A two-layer sheet of phospholipid molecules
-Composed of 2 regions
-Head w/ negatively charged phosphate group
-2 non-polar fatty acid tails
-Non-polar molecules can move across the hydrophobic interior

head w/ negatively charged phosphate group

-hydrophilic
-faces outward, exposed to aqueous solutions on both sides of the membrane

non-polar fatty acid tails

-hydrophobic
-faces inward, mingling together and shielded away from the aqueous solutions
-embeds proteins

prokaryotic cells

-cells that do not have a nucleus or other membrane-bound organelles.
-evolved before eukaryotic cells

Prokaryote

"before nucleus"

examples of prokaryotes

-bacteria
-archaea

eukaryotic cells

cells that contain a membrane-enclosed nucleus & other membrane-bound organelles

Eukaryote

"true nucleus"

examples of eukaryotes

-protists
-fungi
-plants
-animals

Frimbriae

attachment structures on the surface of some prokaryotes

chromosomes

threadlike structures made of DNA molecules that contain the genes

chromatin

-Clusters of DNA, RNA, & proteins in the nucleus of a cell
-Before cell division, chromatin fibers coil up, becoming thick enough to be visible by a light microscope

ribosomes

-Synthesizes polypeptides (proteins) according to instructions from the nucleus
-Can be free/bound

free ribosomes

-Suspended in the fluid of the cytoplasm
-Most proteins made on free ribosomes function within the cytoplasm

bound ribosomes

-Attached to the outside of the endoplasmic reticulum/nuclear envelope
-Synthesizes proteins that could be inserted in the growing ER membrane, transported to other organelles, or secreted by the cell

cytoplasm

-Jelly-like fluid inside the cell that suspends the organelles
-Only refers to the region between the nucleus and plasma membrane in prokaryotic cells

nucleoid

-A dense region of DNA in a prokaryotic cell
-Not surrounded by a membrane
-"Nucleus-like"

nucleus

-Control center of the cell
-Houses most of cell's DNA
-Directs protein synthesis to organize/coil DNA
-Replicates DNA
-Synthesizes RNA (rRNA & mRNA)

DNA

-deoxyribonucleic acid
-associated w/ chromosome proteins

RNA

ribonucleic acid

types of RNA

-messenger RNA (mRNA)
-ribosomal RNA (rRNA)
-transfer RNA (tRNA)

messenger RNA (mRNA)

-Carries instructions from DNA in the nucleus to the ribosomes
-Moves through the pores in the nuclear envelope to the cytoplasm
-Is translated by the ribosomes in the cytoplasm into the amino acid sequence of proteins

ribosomal RNA (rRNA)

makes up part of the ribosome

transfer RNA (tRNA)

carries amino acids to the ribosome

nuclear envelope

-Double membrane that encloses the nucleus of a cell
-Each membrane is a phospholipid bilayer w/ associated proteins
-Controls flow of material in & out of the nucleus
-Perforated w/ protein-lined pores

protein-lined pores (nuclear pores)

-Small holes in the nuclear envelope
-Regulates the movement of molecules in the nucleus
-Connects the nucleus w/ the ER

Nucleolus

-Found inside the nucleus
-Synthesizes rRNA according to DNA instructions
-Assembles ribosomal subunits

step 1 of ribosomal subunit synthesis

Proteins brought in through nuclear pores of the cytoplasm are assembled w/ nucleolus rRNA, forming ribosomal subunits

step 2 of ribosomal subunit synthesis

Subunits then exit through the pores of the cytoplasm, joining to form functional ribosomes

capsule

jelly-like outer coating of prokaryotes

organelles

-"Little Organs"
-Cellular structures that perform specific functions
-Each bounded by a membrane in eukaryotes
-Enzymes essential for metabolic processes are built into the membrane

fluid-filled spaces in organelles

-Maintains chemical conditions
-Chemical conditions vary among organelles

cellular metabolism

All the chemical activities of all the organelles in a cell

1st basic functional group

Nucleus & ribosomes carry out genetic control of the cell

2nd basic functional group

Golgi apparatus; lysosomes; peroxisomes; & vacuoles function in the manufacture, distribution, & breakdown of molecules

3rd basic functional group

Mitochondria in all cells & chloroplasts in plants function in energy processing

4th basic functional group

Cytoskeleton; plasma membrane; & plant cell wall function in the structural support, movement, & communication between cells

animal cell

eukaryotic cells that contain lysosomes & centrioles not found in plant cells

lysosome

-"Breakdown Body"
-A membranous sac of digestive enzymes contained in an acidic environment
-Enzymes & membranes are made by rough ER & processed in the Golgi
-Protists engulf food particles into vacuoles
-Lysosomes fuse & digest food vacuoles, releasing the nutrients in the cell fluid
-Digests damaged organelles, bacteria, macromolecules
-Serves as recycling centers in animal cells

hydrogen peroxide (H2O2) production & degradation in lysosomes

-Enzymes transfer hydrogen from various compounds to oxygen, producing hydrogen peroxide (H2O2) as a byproduct
-Other enzymes convert this to water, degrading H2O2

step 1 of the lysosome recycling process

Damaged organelles/small amounts of cell fluid become surrounded by a membrane

step 2 of the lysosome recycling process

A lysosome fuses w/ such vesicle, dismantling its contents, & making organic molecules for reuse

Centriole

-Helps organize cell division in animal cells
-Found in the microtubule-organizing center

plant cell

-Eukaryotic cells that contain a cell wall, chloroplast, plasmodesmata, & central vacuole not found in animal cells
-Pectins glue adjacent plant cells together

cell wall

-A rigid layer of nonliving material that surrounds the cells of plants & some other organisms.
-Consists of cellulose fibers embedded in polysaccharides & proteins
-Functions as skeletal support, keeping plants upright on land
-Protects the cells
-Binds cells in tissues

cell wall construction

-Plant cells initially lay down a thin, flexible primary cell wall that allows the cell to continue to enlarge
-Some cells add a secondary cell wall, deposited in layers
-Construction is similar to that of fiber glass

chloroplast

-Photosynthetic organelle of plants & algae
-Enclosed by an inner & outer membrane
-Membranes are separated by an intermembrane space
-Inner membrane holds the stroma
-Holds thylakoids, a circular DNA molecule, & ribosomes

Photosynthesis

-Process in which light energy converts carbon dioxide & water into oxygen & glucose

stroma

thick fluid containing chloroplast DNA, ribosomes, & other enzymes

thylakoids

-Network of interconnected membrane sacs inside the chloroplast
-Converts light energy into chemical energy of glucose

thylakoid space

compartment inside thylakoid

granum (grana)

-stack of thylakoids
-green chlorophyll molecules embedded in the membrane trap solar energy

plasmodesma (plasmodesmata)

-Cytoplasmic channels through cell walls that connect adjacent cells
-Cytoplasm & plasma membrane extend through the plasmodesmata
-Allows plant tissue cells to share water, nourishment, & chemical messages

central vacuole

-Helps the cell grow in size by absorbing water, enlarging
-Stockpiles vital chemicals
-Acts as a trash can, safely storing toxic waste products

cytoskeleton

-A network of protein fibers that extend throughout the cytoplasm
-Aids in structural support, cell motility, & movement of organelles within cells
-Anchors organelles
-Includes microfilaments, microtubules, & intermediate filaments

structural support (cytoskeleton)

-Holds the cell together
-Helps the cell keep its shape

cell motility

-Internal movement of cell parts
-Locomotion of the cell
-Requires the interaction of the cytoskeleton w/ motor proteins

examples of cell motility

-Crawling
-Muscle contraction
-Bending of cilia & flagella

microfilaments (actin filaments)

-Thinnest
-Composed of solid rods of actin arranged in a Twisted Double Chain
-Microfilaments form a 3D network inside the plasma membrane to support cell shape
-Involved in cell movements
-Can disassemble & reassemble elsewhere

intermediate filaments

-In between thickness
-Composed of fibrous proteins that supercoil into thicker cables
-Reinforces cell shape
-Anchors certain organelles
-Holds the nucleus in place in a cage
-Are permanent fixtures in a cell

microtubules

-Thickest
-Are straight, hollow tubes composed of tubulins
-Elongates by the addition of tubulin proteins
-Shapes/supports cell
-Acts as tracks where organelles equipped w/ motor proteins can move
-Guides movement of chromosomes during cell division
-Are readily assembled in a reverse manner

tubulins

-Globular proteins that make up microtubules
-Consists of 2 subunits
-Can be reused elsewhere in the cell

microtubule-organizing center

-growth center of microtubules in animal cells
-contains a pair of centrioles within this region

flagellum (flagella)

-Whip-like tails found in one-celled organisms
-Aids in movement
-Most animals & some plants have flagellated sperm
-Composed of microtubules wrapped in an extension of plasma membrane

cilium (cilia)

-Hair-like projections that extend from the plasma membrane
-Used for locomotion
-Propels protists
-Sweeps mucus containing debris in lungs
-Composed of microtubules wrapped in an extension of plasma membrane

primary cilium

-a single, nonmotile attachment which acts as a signal sensor
-lacks the central pair of microtubules
-only one per cell (in vertebrate animals)

9+2 pattern

-The arrangement of microtubules in cilia and flagella
-9 microtubule doublets surround a central pair of microtubules

basal bodies

-a ring of 9 microtubule triplets
-anchors cilia/flagella

dynein protein

-Motor protein
-Drives the bending movements of microtubules in cilia & flagella
-Attached along each microtubule doublet

movement of dynein proteins

-Has 2 "feet" that "walk" along adjacent footing
-1 foot maintains contact; the other foot releases & reattaches 1 step farther along its neighboring microtubule
-Outer doublets are held in place by flexible cross-linking proteins & radial spokes, preventing sliding

Endomembrane system

-A network of membranes inside and around a eukaryotic cell
-Related through direct physical contact or by transfer of membranous vesicles
-Divides the cell into separate functional compartments

organelles of the endomembrane system

-nuclear envelope
-endoplasmic reticulum
-golgi apparatus
-lysosomes
-vacuoles
-plasma membrane

peroxisome

-Metabolic compartments that do not originate from the endomembrane system
-Breaks down fatty acids to be used as cellular fuel
-Detoxifies alcohol & other toxic compounds in liver cells

vesicles

small membranous sacs that specialize in moving products into, out of, & within a cell

vacuole

-Vesicle that stores materials such as water, salts, proteins, or carbohydrates
-Vacuoles in plants can have a digestive function similar to lysosomes
-Vacuoles in flower petals contain pigments that attract pollinating insects
-Can contain poisons/unpalatable compounds (nicotine, caffeine) for protection against herbivores

food vacuole

forms as a cell ingests food

large central vacuole

stores water & other chemicals

contractile vacuole (paramecium)

-balances water
-spokes collect water from the cell
-hub expels it to the outside

Endoplasmic Reticulum (ER)

-Network of flattened sacs & tubules
-Forms a maze of passageways in which proteins & other materials are carried from one part of the cell to another
-Continuous w/ the nuclear envelope
-Can be smooth/rough

endoplasmic

"within the cytoplasm"

reticulum

"little net"

smooth ER

-ER that is free of ribosomes
-Functions in metabolic processes
-Synthesizes lipids
-Detoxifies drugs & alcohol in liver cells, increasing body tolerance
-Stores Ca2+ (muscle cells)

examples of lipids

-oils
-phospholipids
-steroids