The Cell Flashcards
Where did all organisms on Earth come from?
one common ancestral cell (3.5 billion years ago)
theory of endosymbiosis
mitochondria and chloroplasts (free-living prokaryotes) taking up permanent residence inside other larger cells (1.5 billion years ago) creating eukaryotic cells
eukaryotic cells are much more complex cells with internal membrane dividing the cell causing rapid evolution of multicellular organisms
modern cell theory (2)
- all organisms are made of cells
- all cells come from pre-existing cells
What are the sizes of animal and plant cells?
most animal and plant cells have diameters between 10 and 100 μm (many can be smaller, human red blood cells are 8 μm)
cells share 3 characteristics
- enclosed by plasma membrane (protective + selective barrier)
- contain cytosol (semifluid substance) suspending components
- contain ribosomes and genetic material in form of DNA
prokaryotes (7)
- no internal membranes (nucleus is replaced with nucleoid region: non-membrane-bound region with chromosome)
- circular, naked DNA
- small ribosomes
- anaerobic or aerobic metabolism
- no cytoskeleton
- mainly unicellular
- 1-10 μm
eukaryotes (7)
- distinct membrane-bound organelles
- DNA wrapped with histone proteins into chromosomes
- large ribosomes
- aerobic metabolism
- cytoskeleton
- mainly multicellular with different cell types
- 10-100 μm
What is notable about the structure of different cells?
(Different cells have different structures)
Function dictates form, so different cells have different structures depending on the purpose
Examples:
nerve cells long and spindly to send electrical impulses
cells that store fat are rounded, large, distended
cells that make up a peach pit look like square building blocks
Why are cells small?
the surface area of the cell membrane must be able to accomodate the metabolic needs/volume of the cytoplasm
ratio of surface area to volume should be greater (6:1) for more efficiency
as a cell grows and the volume becomes greater, the cell will be divided into 2
nucleolus (5)
- found in the nucleus of a nondividing cell
- synthesises rRNA (ribosomal RNA) as instructed by DNA
- subunits of ribosomes also assembled
- combines the protein from the cytoplasm with the rRNA made
- not membrane-bound, but a tangle of chromatin + unfinished ribosomal precursors
ribosomes (2)
- protein factories
- found free in the cytoplasm or bound to the ER
free = protein produced for the cell’s own use
bound = meant for export out of the cell
peroxisomes (3)
- found in both plant and animal cells
- contain catalase which converts hydrogen peroxide into water with release of oxygen atoms
- detoxifies alcohol in liver cells
hydrogen peroxide = waste product of respiration
endomembrane system
- regulates protein traffic
- performs metabolic functions in cells
- includes: nuclear envelope, ER, Golgi apparatus, lysosomes, vesicles, vacuoles, plasma membrane
nucleus (3)
- contains chromosomes wrapped with special proteins into a chromatin network
- surrounded by selectively permeable nuclear envelope seperating contents of nucleus from cytoplasm
- nuclear envelope has pores to allow for transport of large molecules that can’t diffuse directly through (e.g. mRNA)
endoplasmic reticulum (ER)
- membranous system of channels and flattened sacs that cross the cytoplasm
- has two types: rough and smooth
Rough ER: studded with ribosomes + produces proteins
Smooth ER: has 3 functions
1. assist in synthesis of steroid hormones and other lipids
2. stores Ca++ ions in muscle cells to facilitate normal muscle contractions
3. detoxifies drugs and poisons from body
the ER accounts for more than 50% of the total membranes in eukaryotic cells
Golgi apparatus
- near the nucleus
- flattened membranous sacs stacked next to each other surrounded by vesicles
- process and package substances produced in the rough ER
- secrete the substances to other parts of the cell or surface for export
lysosomes
- sacs of hydrolytic (digestive) enzymes surrounded by a single membrane
- principal site of intracellular digestion
- helps cell continually renews itself by breaking down + recycling cell parts (autophagy)
- programmed destruction of cells (apoptosis) by own hydrolytic enzymes is critical part of development of multicelled organisms
not found in plant cells
mitochondria
- site of cellular respiration
- with outer double membrane and inner series of membranes called cristae
- contains their own DNA
- divide and fuse with each other to exchange DNA to fix defects
mitochondria having their own DNA supports endosymbiotic theory
up to 2500 mitochondria found in an active cell
vacuoles
- membrane-bound structures for storage
- large vesicles from ER and Golgi apparatus
- mature plant cells have single central vacuole
- freshwater protists have contractile vacuoles to pump out excess water
- food vacuoles formed by phagocytosis of foreign material
chloroplast
- contain green pigment chlorophyll that absorbs light energy and synthesizes sugar (along with enzymes)
- found in plants and algae
- double outer membrane with inner membrane system called thylakoids
theory of endosymbiosis: once tiny, free-living prokaryotic cells that were engulfed by a larger prokaryotic cell and eventually become one
have their own DNA that resembles bacterial DNA
cytoskeleton (4)
complex mesh of protein filaments that extends throughout cytoplasm
Important for:
1. maintaining cell shape
2. controls position of organelles within cell by anchoring them to plasma membrane
3. flow of cytoplasm (cytoplasmic streaming)
4. anchors cell in place by interacting with outside element
Has microtubules + microfilaments
parts of the cytoskeleton
microtubules
hollow tubes made of the protein tubulin making up cilia, flagella, and spindle fibers
parts of the cytoskeleton
cilia and flagella
- moves cells from one place to another
- 9 pairs of microtubules organized around 2 singlet microtubules (9 + 2 formation)
| flagella are not made of microtubules in prokaryotes
parts of the cytoskeleton
spindle fibers
- helps seperate chromosomes during mitosis and meiosis
- microtubles organized into 9 triplets with none in the center
parts of the cytoskeleton
microfilaments (3)
assembled from actin filaments and support the shape of the cell
Helps:
1. animal cells form cleavage furrow during cell division
2. amoeba to move by sending out pseudopods
3. skeletal muscle to contrast as they slide along myosin filaments
centrioles, centrosomes, MTOCS (microtubule organizing centers)
- nonmembranous structures that lie outside nuclear membranes
- organize spindle fibers, and give rise to spindle apparatus for cell division
- 2 centrioles at right angles = one centrosome and consists of 9 triplets of microtubules in a circle
plant cells have no centrosomes, but have MTOCs
centrosome = MTOC in animal cell
cell wall
- made of cellulose in plants and algae
- made of chitin in fungi
- consist of polysaccharides + complex polymers in prokaryotes
primary and secondary cell wall
primary cell wall is immediately outside plasma membrane
some cells have second cell wall underneath primary
middle lamella
thin gluey layer between 2 new cells after a plant cell divides
plasma membrane
selectively permeable membrane that regulates what enters and leaves cell
eukaryotic plasma membrane consists of a phopholipid bilayer with proteins dispersed throughout the layers
around 40% lipid to 60% protein
parts of the plasma membrane
integral proteins
nonpolar regions that completely span hydrophobic interior of membrane
parts of the plasma membrane
peripheral proteins
loosely bound to surface of membrane
parts of the plasma membrane
cholestrol molecules
embedded in interior of bilayer to stabilize membrane
parts of the plasma membrane
glycolipids and glycoproteins
carbohydrates covalently bounded to proteins or lipids extending form external surface
may serve as signalling molecules that distinguish cell type
Function of proteins in the plasma membrane
- Transport: molecules, electrons, ions carried through channels, pumps, carriers, and electron transport chain, which manufactor ATP
- Enzymatic activity: adenylate cyclase (membrane-bound enzyme) synthesizes cyclic AMP (cAMP) from ATP
- Signal transduction: binding sites on protein receptors fit chemical messengers (signaling molecule) like hormones, protein changes shape and relays message to the inside of the cell
- Cell-to-cell recognition: some glycoproteins serve as identificant flags that are recognized by other cells
- Cell-to-cell attachments: desomosomes, gap junctions, tight junct ions
- Attachment to the cytoskeleton and extracellular matrix: helps maintain cell shape and stabilizes location of certain membrane proteins
transport
movement of substances into and out of cell
2 types: active or passive
passive transport
movement of molecules down a concentration gradient (from high to low) until equilibrium is reached
diffusion and osmosis
does not require energy
simple and facilitated diffusion
simple does not involve protein channels, but facilitated diffusion does
facilated diffusion requires a hydrophilic protein channel
countercurrent exchange
special case of simple diffusion
flow of adjacent fluids in opposite directions maximizes rate of simple diffusion
osmosis
term used for water across a membrane diffusion
solvent and solute
solvent = substance that does the dissolving
solute = substance that dissolves
hypertonic, hypotonic, and isotonic
hypertonic: having greater concentration of solute than another solution
hypotonic: having lesser concentration of solute than another solution
isotonic: 2 solutions having equal concentration of solutes
osmotic potential
tendency of water to move across permeable membrane into a solution
water potential
- movement of water
- pure water has 0 water potential, addition of solutes lower the value to less than 0
- water moves across a membrane from solution with higher water potential to lower
aquaporins
special water channel proteins found in certain cells to facilitate diffusion of massive amounts of water across membrane
only affects the rate at which water diffuses down its gradient
active transport
movement of molecules against a gradient
requires energy (ATP)
pumps or carriers
examples of active transport
carries particles across membrane by active transport
examples include the sodium potassium pump (pumps Na+ and K+ ions across nerve cell membrane to return the nerve to its resting state) and the electron transport chain (proteins that pump protons across the cristae membrane in mitochondria)
contractile vacuole
examples of active transport
pumps out excess water that is diffused inward
found in freshwater Protista which lives in a hypotonic environment
exocytosis
examples of active transport
vesicles release neurotransmitters into a synapse (nerve cells)
pinocytosis
examples of active transport
cell drinking, uptake of large, dissolved particles
phagocytosis
examples of active transport
engulfing of large particles/small cells by pseudopods
receptor-mediated endocytosis
examples of active transport
enables cell to take up large quantities of specific substances
when extracellular substances bind to receptors on the membrane
bulk flow
overall movement of fluid in one direction in organism
always from source to sink (where it’s used)
quorum sensing in bacteria
cell communication
- bateria monitors population density and uses information to control gene expression
- can allow different bacteria species to communicate
direct contact
cell communication
signalling substances dissolved in cytosol can pass freely between cells by gap junctions or plasmodesmata (plant cells)
local signaling
cell communication
release of local signals
For example: growth factors from cell to nearby cells, gives instructions to grow and divide
synaptic signalling (neuron releases neuro-transmitter into synapse) will stimulate adjacent neuron to fire or a muscle to contract
long-distance signalling
planst use hormones, animals use endocrine glands to release hormones in blood to reach organs/structures
Example: helper T white blood cells can send alarm to entire immune system
Three stages of cell signalling:
- Reception: signal molecule (ligand) from outside target cell binds with receptor on or inside target cell
- **Transduction: **signal converted to form that triggers specific response
- Response: specific response occurs, by regulation of transcription or cytoplasmic action
cell surface receptors
- span entire thickness of membrane, in contact with outside and inside
- hydrophillic signaling molecules cannot diffuse through membrane
- receptor changes shape on the cytoplasmic side and is carried by a second messenger (commonly cyclic AMP or cAMP)
- first messenger (ligand) never enters the cell
cell surface receptors make up 30% of all human protein
3 types of cell surface receptors
- ion-channel
- G protein-coupled
- protein kinase
ion channel receptors
- allosteric receptor that open and shuts gate in membrane, allowing influx of ions (Na+, K+, Ca2+, Cl-)
- basis of normal nerve function
G protein-coupled receptors (GPCR)
- spans cell membrane
- when a ligand (first messenger) binds to outside domain of receptor, it changes conformation of cytoplasmic side of receptor
- activates G protein (on/off molecular switch) which bonds to GTP (high energy nucleotide similar to ATP) that activates enzyme adenylyl cyclase
- enzyme catalyzes conversion of ATP to cyclic-AMP (cAMP) or second messenger
protein tyrosine kinases (RTKs)
- has enzymatic activity
- spans entire membrane
- part of receptor that extends into cytoplasm functions as tyrosine kinase
- before ligand binds, receptors are individual units
- after bind, individual units activate tyrosine kinase region, which bonds to ATP
- after fully activated, receptor activates relay proteins that lead to cellular response
tyrosine kinase = enzyme that catlyzes transfer of phosphate groups from ATP to amino acid tyrosine)
intracellular receptors
- small nonpoplar ligands diffuse through membrane and bind to receptors inside
- hydrophobic chemical messengers: steroids, thyroid hormones, nitric oxide
some substances in environment (like bisphenol A) mimic hormones like estrogen, believed to be responsible for problems in fetal development
transduction
activated receptor converts molecular signal into cell response
transduction can sometimes be done in 1 step, but often takes more
signal transduction pathway
multistep process where little amount of signal molecules produce great response (cascade effect)
good because multistep pathway provides more opportunities to amplify signal
5 things about signal transduction pathway
- characterized by signal, transduction, response
- highly specific and regulated
- 1 signal molecule can cause cascade effect, releasing thousands of molecules inside
- regulate cellular activity, altering gene expression, protein activity, or protein synthesis
- pathways evolved millions of years ago in common ancestor
apoptosis
- programmed death of infected, damaged, aged cell
- DNA, organelles, and other components chopped up, packaged in vesicles, and engulgfed by special scavenger cells
- relies on cell-signallying pathways and outside/inside signals
reasons for apoptosis
- during embryonic development, when cells/tissues are no longer needed and are engulfed by neighboring cells
- sustained too much genetic damage and can lead to cancer (esp skin cells)
- important for defense against infection by fungus/bacteria in plants
- in mammals, several different pathways involving enzymes called caspases carry out apoptosis, signals from inside/outside cell trigger pathways, can be because cell has irreparably damaged DNA in nucleus, or excessive protein misfolding has happened
