cell bio exam 4

cytoskeleton

network of protein filaments extending throughout the cell

types of protein filaments

intermediate filaments, microtubles, actin filaments

intermediate filaments

intermediate in size, heterogeneous family of proteins, provides mechanical strength, tough, durable

microtubules

tubulin protein subunits, long hallow rigid tubes, often rapidly assembled and disassembled

actin filaments

actin protein subunits, flexible, helical filaments, abundant cytoskeletal protein

keratin intermediate filament

in epithelial cells, basal lamina

nuclear lamina

in animal cells, stregthens nuclear envelope

basal lamina

thin sheet of tissue supporting epithelial cells

microtubules have a

+ end and - end

tubulin subunits bound to GTP assemble

when GTP —> GDP they disassemble

microtubules guide transport of

organelles, vesicles, and macromolecules

mitotic spindles

move chromosomes within cell

some stable microtubule structures exist

cilium and flagellum, arranged in characteristic 9+2 array

assembly of actin monomers into polymers requires

ATP

actin binds to various proteins, large range of functions

assists in cell division- ability of cells to move or change shape

motor proteins

proteins able to use energy from ATP hydrolysis to generate motion

motor protein functions

muscle contraction, intracellular movement of organelles and vesicles

3 classes of motor proteins__, have two domains __

myosin, kinesins, dyneins; motor head and cargo binding

myosin

molecules can associate with actin and function in muscle cells, uses ATP to move along an actin filament, in the absence of ATP, myosin won’t move (cause of rigor mortis)

myosin creates a __ in animal cell division, they also assist in the movement of __ in plants and algae

contractile ring; chloroplasts

kinesins and dynesis

different motor proteins transport different types of cargo along microtubules

transport is directional along microtubules

kinesin move toward +, dynesins move toward -

most organelles have 1+

motor proteins associated with them

cell signaling

communication, information, signal, receptor, response, includes communication between cell to cell, and cell to environment

transduction

information can change from one form to another, cells are able to respond to a signal, even though signal doesnt enter cell

cell — cell communication process

molecule produced/released by one cell- signaling cell, received by another cell- target cell (by receptor protein- not always on the surface)

overview of cell signaling

receipt of signal by cell receptor, transmission/transduction of signal into cell, distribution of message within cell, cell response

cell communication

proper receptor required to respond to signal, cell have many different receptors, respond tomany different signals, including combinations of signals

types of signaling molecules

proteins/peptides, nucleotides, lipids, ions, amino acids, gasses

animal cell signaling forms

endocrine, paracrine, neuronal, contact-dependent, autocrine

autocrine

signaling and target cell are the same

endocrine

signals travel long distances via the bloodstream

paracrine

diffuses short distance to nearby cell

signals induce different responses like__, they can also cause different responses in different cells

survive, grow & divide, differentiate, die

receptor proteins

on surface or inside target cell, most signal molecules cant cross membranes, small hydrophobic signaling molecules can cross

3 classes of cell surface receptors

G protein-coupled receptors, ion channel receptors, and enzyme-linked receptors

G protein-coupled receptors __, inactivated when bound to __

comprised of receptor protein, G protein, target protein; GDP, activated when bound to GTP

overview of G protein-coupled receptor

extracellular signal binds to receptor, G protein activated (exchanged GDP for GTP), activated G protein acivates a target protein

target proteins may be:

ion channels or enzyme channels

Most common target protein of G protein receptor

adenylyl cyclase (adenylate cyclase) ATP —> cAMP

cAMP

a major intracellular messenger catalases

cell surface receptors are targets for many foreign substances like

drugs, medicines, and spices

extracellular signals can alter protein activity which alters

cell behavior

when an extra cellular signal is transduced,

a new intracellular signal is generated

signal cascade

pathway amplifies and distributes intracellular signals

types of second messengers

cyclic nucleotides (cAMP), lipid molecule (IP3, DAG), Ca2+, NO (nitric oxide)

ATP —> cAMP

major secondary messenger

Phospholipase C

membrane-associated enzyme, breaks down plasma membrane phospholipids, produces DAG and IP3

Ca2+

mechanisms are needed to keep low background levels in cytosol, Ca2+ moves out of the cell

NO

diffused across membrane, short half life (5-10 secs), nitroglycerine, sildenafil

NO ex. Nitroglycerine

dilates blood vessels, increases blood flow to heart

sildenafil

dilates blood vessels, increases blood flow to the penis

cellular response to extracellular signals: rapid

modification of activity of existing proteins

cellular response to extracellular signals: slow

altered gene expression

signaling pathways

often complex, highly integrated, challenging to elucidate

cell cycle

life of a cell, new cells are produced by division of existing cells, has both growth and division

phases

when cells reproduce

DNA is replicated, new proteins and membranes synthesized, distribution of cell contents

4 phases of cell cycle

G1, S, G2, M, first 3 phases are interphase or growth phases

G1

new daughter cells begin life, cell grows, increase in cytoplasmic contents

S

DNA replication

G2

cell growth and preparation for division

M

mitosis or meiosis, nucleus divides first then the cytokinesis (cytoplasic division)

nuclear division + cytoplasmic division =

cell division

celll cycle highly regulated by

cyclins and cycle-dependent kinases- cell regulatory proteins

major checkpoints of the cell cycle

prior to S phase, prior to M phase, during M phase

p53 gene

codes for p53 protein- a tumor suppressor gene

p53 protein

inhibits progression of cell cycle, accumulates when DNA is damaged, prevents cell from entering S phase

mitosis

occurs during the formation of gametes

gametes

sex cells (sperm, egg)- have 1 set of chromosomes: haploid (1n)

somatic cells

all cells other than gametes, have 2 sets of chromosomes: diploid (2n)

cytokinesis

division of cytoplasm, divides by cleavage, in plant cell includes formation of new cell wall

cell defense

different cells utilize different mechanisms of defense, Plants: physical and chemical, animals: vertebrate immune system

physical cell defense in plants

cell wall (support and protection), surfaces covered by cuticle (fatty acids: waxes, resists pathogens and conserves water)

chemical defense mechanism of plants

secondary metabolites- main role of defense and communication (no direct role in growth/development)

chemical examples

Pharmaceuticals, food flavorings, natural dyes, cosmetics, industrial materials, insecticides; hypersensitive response (defense, cell accumulates toxins, cell death)

vertebrate immune system

innate immune system- induced following infection/attack, antibody proteins, highly specific

antibodies

protein molecules, produced by vertebrate immune system

antigen

antibody generator; ligands, bind tighly to antibodies

B cell

(lymphocyte) white blood cell, produce antibodies

how a large number of antibodies are generated

combinations of polypeptides, recombination of DNA sequences, alternate splicing of mRNA, mutations

necrosis

death from damage or injury

necrosis characteristics

affects groups of cells, cell swells and bursts, plasma membrane ruptures, inflammatory response, occurs slowly

apoptosis

programmed cell death, first reported in 1972, cellular components broken down

apoptosis is initiated by

mitochondria through extrinsic or intrinsic pathway

cascades

activated by a cascade process

apoptosis characteristics

affects individual cells, cell shrinks; cytoplasm contracts, plasma membrane remains intact, no inflammatory response, occurs rapidlyy

intrinsic pathway

initiated by internal signal

extrinsic pathway

initiated by external signal

intracellular initiation of apoptosis (intrinsic pathway)

mitochondria and cytochrome C play key roles

cytochrome C

protein in ETC released from mitochondria

apoptosis kills cells that

are generated in excess, develop improperly, have completed their function

apoptosis in plants

hypersensitive response, formation of vascular tissues

extracellular matrix

tissues comprised of cells and extracellular matrix, located between cells in tissues, provides strength to tissues, in plants the cell wall is ECM

ECM is made from

polysaccharides and proteins, secreted by cells

plant cell walls comprised of

cellulose fibers, and other polysaccharides, and proteins walls are strong and tough

ECM in animals

abundant in connective tissue, lesser amounts in other tissues (bones, tendons, cartilage, interior of the eye)

collagen fibers are

major protein in animal ECM

epithelial tissues

sheets of cells covering external both surfaces, lining of internal body cavity, cells sit on the basal lamina- thin sheet of ECM

epithelial sheets are polarized

two surfaces are asymmetrical, apical surface is free and exposed, basal surface attached to basal lamina

cell junctions

tight junction, adherent junction, desmosome, hemidesmosome, gap junction