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Chapter 2: Cells and Organelles
Terms in this set (92)
hold cellular contents and are mainly composed of phospholipids, cholesterol, and proteins
glycerol backbone, one phosphate group, and two fatty acid tails. amphipathic
molecules have both polar and non polar parts, allowing them to form a lipid bilayer in an aqueous environment
four fused hydrocarbon rings and is a precursor to steroid hormones. Also amphipathic and helps regulate membrane fluidity
either integral or peripheral membrane proteins
integral (transmembrane) proteins
traverse the entire bilayer, so they must be amphipathic. Their non polar parts lie in the middle of the bilayer while 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
found on the outside of the bilayer, and they are generally hydrophilic
trigger secondary responses within the cell for signaling
attaches cells to other things (eg. other cells) and act as anchors for the cytoskeleton
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"). Furthermore, the cell membrane contains many different kinds of structures
The fluidity of the cell membrane can be affected by:
Degrees of unsaturation
How does temperature affect fluidity of the cell
increase temperatures increase fluidity while decrease temperatures decrease it
How does cholesterol affect fluidity of the cell
holds membrane together at high temperatures and keeps membrane fluid at low temperatures
How does degrees of unsaturation affect fluidity of the cell
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
flow of small, uncharged, non polar substances (eg. O2 and CO2) across the cell membrane down their concentration gradient (high to low) without using energy
a type of simple diffusion that involves water molecules (water is polar, bit is small enough to cross the membrane
integral proteins allow larger, hydrophilic molecules to cross the cell membrane
single substance, single direction
two substances, same direction
two substances, opposite directions
type of facilitated transport that is performed by channel proteins, bringing molecules down their concentration gradient without energy use.
ex. porins and ion channels
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. For example the sodium-potassium (Na/K) pump establishes membrane potential
secondary active tranport
uses free energy released when other molecules flow foes their concentration gradient to pump the molecule of interest across the membrane
bulk transport of large, hydrophilic molecules across the cell membrane and requires energy (active transport mechanism)
involves the cell membrane wrapping around an extracellular substance, internalizing it into the cell via a vesicle of vacuole
different forms of endocytosis
phagocytosis, pinocytosis, receptor-mediated endocytosis
cellular eating around solid objects
cellular drinking around dissolved material (liquids)
requires the binding of dissolved molecules to peripheral membrane receptor proteins, which initiates endocytosis
is the opposite of endocytosis, in which a material is released to the extracellular environment through vesicle secretion
cellular compartments enclosed by phospholipid bilayers (membrane bound). They are located within the cytosol and help make up the cytoplasm
aqueous intracellular fluid
cytosol and organelles
Only ________ cells contain membrane-bound organelle.
primary functions to protect and house DNA. DNA replication and transcription (DNA ->mRNA) occurs here
the cytoplasm of the nucleus
the membrane of the nucleus. It contains two phospholipid bilayers (one inner, one outer) with a perinuclear space in the middle
holes in the nuclear envelope that allow molecules to travel in and out of the nucleus
provides structural support to the nucleus, as well as regulating DNA and cell division
dense area that is responsible for making rRNA and producing ribosomal subunits (rRNA + proteins)
not considered to be organelles: they work as small factories that carry out translation (mRNA -> protein). They are composed of ribosomal subunits
Eukaryotic ribosomal subunits
(60S and 40S) assemble in the nucleoplasm and are then exported from the nucleus to form the complete ribosome in the cytosol (80S). (Note: S does not refer to mass, but to sedimentation characteristics)
Prokaryotic ribosomal subunits
(50S and 30S) assemble in the nucleoid and form the complete ribosome in the cytosol (70S).
make proteins that function in the cytosol while ribosomes embedded in the rough endoplasmic reticulum make proteins that are sent out of the cell or to the cell membrane
rough endoplasmic reticulum (rough ER)
continuous with the outer membrane of the nuclear envelope and is "rough" because it has ribosomes embedded in it.
Proteins synthesized by the embedded ribosomes are sent into the _________ for modifications
lumen (outside of the rough ER)
smooth endoplasmic reticulum
not continuous with other membranes. Its main function is to synthesize lipids, produce steroid hormones, and detoxify cells
made up of cistern that modify and package substances. Vesicles come from the ER and reach the cis face (side closest to ER) of the gold apparatus. Vesicles leave from the trans fave (side closest to cell membrane)
membrane-bound organelles that break down substances (through hydrolysis) taken in through endocytosis. They contain acidic digestive enzymes that function at a low pH. They also carry out autophagy and apoptosis
the breakdown of the cell's own machinery for recycling
programed cell death
transport materials between organelles
temporarily hold endocytosis food, and later fuse with lysosomes
very large in plants and have a specialized membrane called the tonoplast. Function in storage and material breakdown
helps maintain cell rigidity by exerting turgor
store starches, pigments, and toxic substances
found in single-celled organisms and works to actively pump out excess water
group of organelles and membranes that work together to modify, package, and transport proteins and lipids that are entering or exiting a cell. It includes the nucleus, rough and smooth ERs, Golgi apparatus, lysosomes, vacuoles, and cell membrane
perform hydrolysis break down stored fatty acids, and help with detoxification. These processes generate hydrogen peroxide which is toxic since it can produce reactive oxygen species (ROS)
ROS damage cells through
peroxisomes contain an enzyme called
catalase, which quickly breaks down hydrogen peroxide into water and oxygen
the powerhouses of the cell, producing ATP for energy use through cellular respiration
found in plants and some protists. They carry out photosynthesis
organelles found in animal cells containing a pair of centrioles. They act as microtubule organizing centers (MTOCs) during cell division
provides structure and function within the cytoplasm
the smaller structure of the cytoskeleton, and are composed of a double helix made of two actin filaments. They are mainly involved in cell movement and can quickly assemble and disassemble
cyclosis (cytoplasmic streaming)
stirring of the cytoplasm; organelles and vesicles travel on microfilament "tracks"
during cell division, actin microfilaments form contractile rings that split the cell
action microfilaments have directionality, allowing myosin motor proteins to pull on them for muscle contraction
are between microfilaments and microtubules in size. They are more stable than microfilaments and mainly help with structural support. For example, keratin is an important intermediate filament protein in skin, hair, and nails. Lamins are a type of intermediate filament which helps make up the nuclear lamina, a network of fibrous intermediate filaments that supports the nucleus.
are the largest in size and give structural integrity to cells. They are hollow and have walls made of tubular protein dimers. Microtubules also have functions in cell division, cilia, and flagella
kenesin and dynein
motor proteins that transport cargo along microtubules
microtubule organizing centers (MTOCs)
are present in eukaryotic cells and help organize microtubule extension
are hollow cylinders made of nine triplets of microtubules (9x3 array)
contain a pair of centrioles oriented at 90 degree angles to one-another. They replicate during the S phase of the cell cycle so that each daughter cellafter cell division has one centrosome.
cilia and flagella
have nine doublets of microtubules with two singles in the center (9+2 array). They are produced by a basal body, which is initially formed by the mother centriole (older centriole after S phase replication).
extracellular matrix (ECM)
provides extracellular mechanical support for cells
Proteoglycan - a type of glycoprotein that has a high proportion of carbohydrates.
Collagen - the most common structural protein; organized into collagen fibrils (fibers of glycosylated collagen secreted by fibroblasts).
Integrin - a transmembrane protein that facilitates ECM adhesion and signals to cells how to respond to the extracellular environment (growth, apoptosis, etc.).
Fibronectin - a protein that connects integrin to ECM and helps with signal transduction.
Laminin - behaves similarly to fibronectin. Influences cell differentiation, adhesion, and movement. It is a major component of the basal lamina (a layer of the ECM secreted by epithelial cells).
are carbohydrate-based structures that act like a substitute ECM because they provide structural support to cells that either do not have ECM, or have a minimal ECM. They are present in plants (cellulose), fungi (chitin), bacteria (peptidoglycan), and archaea.
is a glycolipid/glycoprotein coat found mainly on bacterial and animal epithelial cells. It helps with adhesion, protection, and cell recognition.
Cell-matrix junctions (connect ECM → cytoskeleton):
Focal adhesions - ECM connects via integrins to actin microfilaments inside the cell.
Hemidesmosomes - ECM connects via integrins to intermediate filaments inside the cell.
Cell-cell junctions (connect adjacent cells):
1. Tight junctions - form water-tight seals between cells to ensure substances pass through cells and not between them.
Desmosomes - provide support against mechanical stress. Connects neighboring cells via intermediate filaments.
Adherens junctions - similar in structure and function to desmosomes, but connects neighboring cells via actin microfilaments.
Gap junctions - allow passage of ions and small molecules between cells.
Plant cells contain a few unique cell junctions:
Middle lamella - sticky cement similar in function to tight junctions.
Plasmodesmata - tunnels with tubes between plant cells. Allows cytosol fluids to freely travel between plant cells.
have the same solute concentration as the cells placed in them.
have a higher solute concentration than the cells placed in them, causing water to leave the cell (cell shrivels).
have a lower solute concentration than the cells placed in them, causing water to enter the cell (cell swells up).
is the bursting of a cell when too much water enters.
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