bio ch 2: cells and organelles Flashcards
cell membranes
hold cellular contents and are mainly composed of (1) phospholipids and (2) proteins with (3) small amounts of cholesterol
phospholipids
glycerol backbone, one phosphate group (hydrophilic), and two fatty acid tails (hydrophobic)
- amphipathic: the molecules have both polar and nonpolar parts, allowing them to form a lipid bilayer in an aqueous environment
cholesterol
has four fused hydrocarbon rings
- precursor to steroid hormones
- amphipathic and helps regulate membrane fluidity
membrane proteins
are either integral or peripheral membrane proteins
integral (transmembrane) proteins
traverse the entire bilayer, must be amphipathic
- their nonpolar parts lie int he middle of the bilayer
- their polar ends extend out into the aqueous environment on the inside and outside of the cell
- usually assist in cell signaling or transport
peripheral membrane proteins
are found on the outside of the bilayer, and they are generally hydrophilic
receptor proteins
trigger secondary responses within the cell for signaling
- if a receptor protein transmits a signal all the way through the lipid bilayer, it is considered an integral protein
drugs that bind to receptors
can either be agonists or antagonists
agonists
are molecules that bind to receptors and functionally activate a target
antagonists
bind and prevent other molecules from binding, inhibiting production of a response
adhesion
attaches cells to other things (e.g. other cells) and act as anchors for the cytoskeleton
cellular recognition
proteins which have carbohydrate chains (glycoproteins)
- used by cells to recognize other cells.
fluid mosaic model
describes how the components that make up the cell membrane can move freely within the membrane (“fluid”)
- the cell membrane contains many different kinds of structures (“mosaic”)
the fluidity of the cell membrane can be affected by
● Temperature - ↑ temperatures increase fluidity while ↓ temperatures decrease it.
● Cholesterol - holds membrane together at high temperatures and keeps membrane fluid at low temperatures.
● Degrees of unsaturation - saturated fatty acids pack more tightly than unsaturated fatty acids, which have double bonds that may introduce kinks .
- Trans-unsaturated fatty acids pack more tightly than cis-unsaturated fatty acids (which have a more severe kink).
three types of transport across the cell membrane
- simple diffusion
- facilitated transport
- active transport
simple diffusion
flow of small, uncharged, nonpolar substances (e.g. O2 and CO2) across the cell membrane down their concentration gradient (high to low) without using energy
osmosis
is a type of simple diffusion that involves water molecules
- water is polar, but is small enough to cross the membrane
facilitated transport
integral proteins allow larger, hydrophilic molecules to cross the cell membrane
- proteins can be uniporters, symporters, or antiporters
- proteins can also be classified as channel proteins or carrier proteins
uniporters
single substance, single direction
symporters
two substances, same direction
antiporters
two substances, opposite directions
channel proteins
open tunnels that face both sides of bilayer
carrier proteins
bind to a molecule on one side and change shape to bring it to the other side
passive diffusion
is a type of facilitated transport that is performed by channel proteins
- bring molecules down their concentration gradient without energy use
- similar to simple diffusion, but a protein channel is used
- e.g. porins for hydrophilic molecules and ion channels for ions
active transport
substances travel against their concentration gradient and require the consumption of energy by carrier proteins
primary active transport
uses ATP hydrolysis to pump molecules against their concentration gradient
- e.g. the sodium-potassium (Na+/K+) pump establishes membrane potential
secondary active transport
uses free energy released when other molecules flow down their concentration gradient to pump the molecule of interest across the membrane
- the gradient is established by primary active transport
cytosis
refers to the bulk transport of large, hydrophilic molecules across the cell membrane and requires energy
- active transport mechanism
endocytosis
involves the cell membrane wrapping around an extracellular substance, internalizing it into the cell via a vesicle or vacuole
different forms of endocytosis
phagocytosis, pinocytosis, receptor-mediated endocytosis
phagocytosis
cellular eating around solid objects
pinocytosis
cellular drinking around dissolved materials (liquids)
receptor-mediated endocytosis
requires the binding of dissolved molecules to peripheral membrane receptor proteins
peripheral membrane receptor proteins
initiates endocytosis
clathrin
is a protein that aids in receptor mediated endocytosis by forming a pit in the membrane that pinches off as a coated vesicle
- this is known as clathrin mediated endocytosis
exocytosis
is the opposite of endocytosis, in which material is released to the extracellular environment through vesicle secretion
organelles
are cellular compartments enclosed by phospholipid bilayers (membrane bound)
- they are located within the cytosol and help make up the cytoplasm
- only eukaryotic cells contain membrane-bound organelles
- prokaryotes do not contain membrane-bound organelles but they have other adaptations, such as keeping their genetic material in a region called the nucleoid
- ribosomes not considered to be organelles
cytosol
aqueous intracellular fluid
cytoplasm
cytosol & organelles
nucleus
primarily functions to protect and house DNA
- DNA replication and transcription (DNA → mRNA) occurs here
nucleoplasm
the cytoplasm of the nucleus
nuclear envelope
the membrane of the nucleus
- contains two phospholipid bilayers (one inner, one outer) with a perinuclear space in the middle
nuclear pores
holes in the nuclear envelope that allow molecules to travel in and out of the nucleus
nuclear lamina
provides structural support to the nucleus, as well as regulating DNA and cell division
nucleolus
a dense area that is responsible for making rRNA and producing ribosomal subunits (rRNA+proteins)
ribosomes
work as small factories that carry out translation (mRNA → protein)
- composed of ribosomal subunits
- not considered to be organelles
eukaryotic ribosomal subunits
60S and 40S
- assemble in the nucleoplasm and then are exported rom the nucleus to form the complete ribosome in the cytosol
- S refers to sedimentation characteristics
- eukaryotic complete ribosome (in cytosol): 80S
prokaryotic ribosomal subunits
50S and 30S
- assemble in the nucleoid and form the complete ribosome in the cytosol
- prokaryotic complete ribosome (in cytosol): 70S
free-floating ribosomes
makes proteins that function in the cytosol
ER ribosomes
ribosomes that are embedded in the rough endoplasmic reticulum (rough ER)
- makes proteins that are sent out of the cell or to the cell membrane
rough ER
continuous with the outer membrane of the nuclear envelope
- “rough” because it has ribosomes embedded in it
- proteins synthesized by the embedded ribosomes are sent into the lumen for modification
- afterwards they are either sent out of the cell or become part of the cell membrane
lumen
inside of the rough ER
smooth ER
smooth endoplasmic reticulum, not continuous with other membranes
- main function is to synthesize lipids, produce steroid hormones, and detoxify cells
Golgi apparatus
stores, modifies, and exports substances that will be secreted from the cell
- made up of cisternae (flattened sacs) that modify and package substances
- vesicles come from the ER and reach the cis face of the Golgi apparatus
- vesicles leave the Golgi apparatus form the trans face
cis face of Golgi apparatus
the side closest to the ER
trans face of Golgi apparatus
the side closest to the cell membrane
lysosomes
membrane-bound organelles that break down substances that are taken in through endocytosis (break down by hydrolysis)
- contains acidic digestive enzymes that function at a low pH
- carries out autophagy and apoptosis
autophagy
the breakdown of the cell’s own machinery for recycling
apoptosis
programmed cell death
proteasomes
protein complexes that degrade unneeded or damaged proteins by proteolysis
- such proteins have a ubiquitin molecule attached, tagging these proteins for degradation
types of vacuoles
transport, food, central, storage, contractile
transport vacuole
transport materials between organelles
food vacuoles
temporarily hold endocytosed food, and later fuse with lysosomes
central vacuoles
very large in plants and have a specialized membrane called the tonoplast
- functions in storage and material breakdown
tonoplast
in central vacuoles
- helps maintain cell rigidity by exerting turgor
storage vacuole
store starches, pigments, and toxic substances
contractile vacuoles
found in single-celled organisms and works to actively pump excess water
endomembrane system
composed of the different membranes that are suspended in the cytoplasm within a eukaryotic cell
- it is a group of organelles and membranes that work together to modify, package, and transport proteins and lipids that are entering or exiting a cell
- the components includes: the nucleus, rough and smooth ERs, Golgi apparatus, lysosomes, vacuoles, and cell membrane
peroxisomes
perform hydrolysis, break down stored fatty acids, and help with detoxification
- these processes generate hydrogen peroxide
- hydrogen peroxide = toxic, it can produce reactive oxygen species (ROS)
- peroxisomes contain an enzyme called catalase → quickly breaks down hydrogen peroxide into water and oxygen
mitochondria
powerhouse of the cell, produces ATP for energy use through cellular respiration
- mitochondrial inheritance is maternal, meaning that all mitochrondrial DNA in humans originates from the mother
chloroplasts
found in plants and some protists
- carries out photosynthesis
- type of plastid
plastid
double-membraned organelles found exclusively within plant cells and algae
- functions in photosynthesis and storage of metabolites
centrosomes
organelles found in animal cells containing a pair of centrioles
- they act as microtubule organizing centers (MTOCs) during cell division
cytoskeleton
provides structure and function within the cytoplasm
