mod 3 chap 3 Flashcards
Cell theory
- all organisms made up of cell
- cell is fundemental unit of life
- cells come from prexisting cell
organsims are made up of cell - some unicellular, others multicellular - in multicelular organisms, the cells are specialized to carry out diff function
cells are fundmental unit of life - cell is the simplest entity that we can define as living - ability to reproduce, respond to envirnment, harness energy, evolve, etc. - cells have these features - they are the smallest most basic unit of life - no life without cells
cells arise from prexisting cell - cell division
prokayrote v eukaryote
Cells of prokayrotes lack nucelus while cells of uekayrotes have nucelus in which geentic material is housed
in prokaryotes the genetic material is in ciruclar chormsome in discrete region kown as nuceloid - have cell wall - sometimes have flagella - small in size - high ratio of surface area to vol which allows them to absorb nutreints from envrinment
eukaryotic cells are bigger - have extensive internal array of membranes - membranes deifne compartments knwon as organelles that divide the cell conetnts into smaller spaces pecilzied for diff fucntions - organelles carry out diff functions - nucleus is exmaple of organelle which has linear chromsomes - nucelus allows for complex regulation of gene expression because the process of tarsncription and transaltion are sperated in space and time
Cell Membranes
all cells are defined by membranes
they physically seperate cells from extrenal anvirnment and define space within that allow tme to carry out diverse functions
lipids are main component of membrane - have property that allow them to form a barrier in an aq enrvinemnt
proteins are embedded or asocciated with the membrane and there thy perform imprnat fucntions like trasnporting molecules
carbs can be found in cell membranes, usually attached to lipids (glycolipids) and proteins (glycoproteins)
lipids in cell membrane
major type of lipid in cell membranes is phospholipids
made up of glycerol backbone attachd to phshate group and two fatty acids
phosphat ehead is hydrophilic bc polar allowing it to form H bonds but the two fatty acid tails are hydrophobic - therefore molecule is amphipathic
in aq envrinments amphipathic molecules will arrange themselves into strcutures where polar head is on outside interatcing with water and nonpolar tails come together on inside away from water - results from tendency of polar molecules exlcuding nonpolar molecules
shape of strctures formed by phospholipids depends on bulkiness of head group relative to the hdyrophobic tails
- lipids with bulky head and single fatty acid tail are wedge shaped and packed into spherical strycres called micelles
- lipids with less bulky head and two fatty acid tails are roughly rectnagular and form bilayer
- when phospholipids are added to test tube of water at pH7 they sponatnesouly form a spherical bilayer strcyure called liposomes that surround a central space, resmbling a cell - bilayers form closed stryctyres with an inner space beacuse free edges would expose the hydrphobic chains to aq envrinment
small tears in a membrane are rapidly sealed by spontanous rearrangemnt of lipids becaus etendecy of water to exlcude nonpolar molecules
liposome tells us how life mightve orignated - strcture forms spontanously as long as cocn of free phosphilipds is high enough and teh pH of solution is neutral - pH is improant because it ensures that head groups are in ionized/charged form and suitibaly hydrophilic - as lipsome forms they may capture macrmolecuels in the solution
Dynamic cell membrane
Lipids freely associate with one another because of the extensive van der waal forces between teh fatty acid tails - these inetraction break and reform so lipid moelcules can move within plane of memebrane
lipids can move around vertical axis and indidual fattya cid chain can flex or bend
as a result memrbanes are dynamic - they are continually moving, forming and reforming
bc lipid can move in plane, membrane is called fluid
fluidity depends onlength and number of cc double bonds in fatty acid tails - longer the tail, less fluid because theres more surface area for waal interaction which would limit lipids to lateral moveemnts - the fewer cc double bonds, the less fluid because they are straight and tightly packed tails which reduce movility
celll membranes also have cholesterol which infleucnes fluidity - amphiptahic - hydrophilic is hydroxyl and hydrophoic are the 4 rings - this allows cholestrol to insert self into lipid bilayer so head interacts with hydrophicl head of phospholipids and the rings interact with fatty acid chain
- effect of cholesterol on fludity depends on temp - at high temp, cholestrol decrease membrane fluidty as the rigid ring strcure of cholestrol interacts with the tails which reduced movility - at low temps fluidty increases as choelstrol prveents phosphilpids from packing tightly
some specific lipids with assemble into defined patches called lipid rafts - cholestrol and othe rmerbane components like proteins appear to accumlate in these areas - membranes arent unfirm fluid bilayer
movement of lipid between layers - lipid flip flop- is rare because it require hdryphilic head to pass through hdyrphibc inetrior - little exchnage of compnents occurs between two layers of membrane which allows the two layers to differ in composioton
proteins associated with cell memrbanes
memrbane proteins serve diff fucntions
some act as trasnporters, moving ions or moelcules across membrane
Others acts as recpetors which allow cell to receive signals from enrbinment
Others are still enzymes which catalyze chem rxns or anchros that attach to other rpoetins and hekpt to maint cell strcture and shape
integral memrbane proteins are permamently ascoiated with teh cell membrane and cant be speerated from membrane without destroyin membrane itself
peripheral membrane proteins are temporarily assocauedt with the bilayer or with inetrnal membrane proteins through weak noncovalent interactions - they are easily seprated
most inetrgral proetins are transmembrane menaing they span the entire lipid bilayer - have three regions: two hydrphilic regions and one hydrophibc region which is inside the membrane
peripheral memrbanes may be associated withe ither internal or external side of membrane - only transently ascoaetd with membrane and can play a role in trasnmitting ifno received from external signals - other peripherla membran eproteins limit the ability of transmemrbane proteins to move within memrbane and assist proteins in clustering in lipid rafts
proteins arefree to move in membrane
fluid mosaic model
idea that lipids, proteins and carbs coexist in membrane and that they are able to move in plane led singer and nicolson to proose this model
accoridng to this model, the lipid bilayer is structure within which molecules move laterally (its fluid) and is a mixture (mosaic) of diff types of molecules
Cell mmebrane and homeostasis
Active maintance of stable envirnment within cells and orgnaisms is homeostaiss - cirtcial atrartibue of cells and life
Cell membrane is seletvly permeable - allows some moelcules in and out
membranes ability to act as selective barrier is result of combo of lipids and embedded proteins of which it is composed
hydrphobic ineterior of bilayer prevents ions and charged polar moelcuels from crossing
many macromoelcules are too large to cross the membrane
gasses and nonpolar moelcules can move across the bilayer
Small uncharged polar moelcules are able to move trhough but to an extent
Protein transprters in emmrbane can faciliate moevemnt of molecules that cant cross bilayer on their own
idenity and abundacne of membrane associated porteins vary among cell types, reflecting specific fucntions of diff cells
Passive transprot
Net movement of molecules can occur form one region to another when there is a con gradient in distrubtion of moleucles (area of high adnd low conc)
Net moevemt of substances from areas of high to low cocn is called diffsuion - when no more gradient, net moevemnt stops but random motion continues
passive transport- occurs when molecules move across a cell memrbane by diffsuion - move as result of differences in cocn between insde and outside of cell
- some moelcules diffsue directly through membrane through simple diffsuion
- passive trasnport also cocurs when moelcules move down cocn gradient through protein trasnported - passive transport by facilitated diffsuion - molecules move rthough a memrbane trasnporter - channel proteins provide opening between inside and outside of cell allowing certain molecules to pass dpeneing on shape and charge (can be gated) - carrier proteins bind to and trasnport specific molecules (open on one side, binds to moelcule and changes conformation and then allows the transports and dumps it on other side)
water move trhough passive trasnprot - moves through channel proteins called aquaporins - allow water to move more readily than how much moves through simple diffsuion
- net movement of water across memebrane is known as osmosis - water moves froma reas of high water cocn to areas of low water conc or low solute conc to high solute cocn
- during osmsi waters net movement happens until cocn gradient doesnt exist or until moevemnt is opposed by another force like pressure by gravity or cell wall - osmosis can be prevented by aplying force to compartment with igh solute conc
- osmotic pressure describes tendency of solutoon to draw water in by osmosis - high solut ocnc higher osmotic pressure
Primary active transport
Movement of susbatnces AGAINt cocn gradient is active transoprt - requires input of energy either diretcly or indirectly
duirng active transport, cells move susbtances through transport proteins embedded in cell membrane - some protein act as pump usng enegry to move susbatcne in or out of cell
ative transport that uses enegry of ATP directly is prmary active trasnport
protein transporter that transport moelcules in diff direction are antiporters and transporters that move in same direction are symporters
Secondayr active transport
Many cells have transport proteins that buildup conc of small ion on one side - resulting cocn gradient stores enegry that can be harnessed to dirve movement of otehr ussbatnces across the memrbane gaainst their cocn gradient - secondayr active transport
gradient with both chem and eletcrial compnents is kown as electrochemcial gradient
secodnary active transport uses potential enegry of electrochemcial gradient to dirve movement of molecules
cells maintaing size and comp using active trasnport
many cells use active transport to maintain their size
Animal cells solve prob of water moevemnt by keeping intracellular fluid isontonic with extracellular fluid - cells use active trasnprot of ions to maintina equal conc insie and out - soidum potassiump pump plays imprtant role in keeping the cell isontinc with extraclelular fluid
contractile vacuoles are organelles that take up excess water from insdie cell and then by contacton expel it into external envirnment
Cell wall and cystoskeleton
Cells have other strageies to mainatin theri shape
many organism have cell wall which miantins cell shape and szie
cell wall made up of cabrs and proteins - plant cell wall made up of poksycharides including celulose - fungi have cell walls of chitin
cell walls provide structral support and proetction for cell - its rigid and resist expansion - allows pressure to build up whne water enter cells - the force exerted by water pressing against an object is turgor pressure - turgor pressure builds as result of water mving by osmis ino cells surroudned by cell wall
vacuole absorbs water and contributes to turgor pressure - inc of turgor pressure keeps the shape in cell wall
shape of cell also dpeends on protein filaments called cytoskeleton - provide inetrnal support for cell - can also allow cells to change shape, move about and tarsnport susbayces within cell
Endomembrane system
membranes of organelles are eithe rphsyically connected by membranes bridges or transiently connected by vesicles, small membrane encolsed sacs that trasnport susbatnces within a cell or from the interir to exterior
- vesicles form by budding off an organelles, taking with them a piece of the membrane and internal conents of organelle from which they derive - they then fuse with another organelle or cell, reforming continous membrane and unloading conents
interconencted mmebranes makeup endomembrane system - includes nucelar envelope, ER, gogli, lyssoomes, cell memrbane and vesicles that move between them
in plants endomembrane system is continous between cells through plasmodesmata
endomembrane system divides interior of cell into two spaces: one inside the compartments defined by membranes and one outside of the compartments
vesicles bud off from and fuse with organelles and with teh clel membrane
- whne vesicle fuses with cell membrane, the process is exoctosis - vesicle empties conents into extracellular space or deliver porteins in vesicle memrbane to cell membrane
- vesicle can bud off cell membrane enclsong material from oysdie and bringing insde which is enocytsosi
nuclear envelope
innermost organelle of endomembrane system is nucelus whihc houses DNA
Nuclear enevelope deifne boudnary of nucelus - conssts of inner and outer membrane both which are lipid bilayer - they are continous with eachothe at nucelar pores - protein compelxes that allow moelcules to move in and out of nucelus
nucelar envelope and pores regulate which moelcules move in and out of nucelus
after exting nucelus, mRNA bidns to ribosomes which are site of protein synthesis - there are ribosomes in cytosol and ribsomes with ER
