Exam 2 Flashcards
Cell Theory
Unifying principle of biology:
- Cells are fundamental unit of life
- All organisms are made of cells.
- All cells come from preexisting cells
- Modern cells evolved from a common ancestor
Site of cellular transport of nutrients and waste for all cells
Cell membrane
Cellular intake of nutrients and release of waste products happens faster when what ratio is higher
Surface area to volume
What limits how big a cell can get
Surface area
Components of all cells
- Cell Membrane: Outer boundary of every cell; phospholipid bilayer with embedded proteins
- Cytoplasm: Everything in cell (except nucleus if applicable)
- Cytosol: Fluid cytoplasm not contained inside other compartment.
What organelles do prokaryotic cells have that eukaryotic cells don’t
Nucleoid, cell wall, capsule (not in all prokaryotes)
Prokaryotic cell walls are polymers of
Peptidoglycan
Difference between gram negative and positive bacteria
Gram negative bacteria have a thin peptidoglycan cell wall surrounded by a polysaccharide-rich outer membrane (rod-shaped) vs positive bacteria that have no outer membrane but have layers of thick peptidoglycan cell wall (spherical)
Hairlike structures that help bacteria adhere to other cells
Pili
Used by prokaryotes to swim, made from protein flagellin
Flagella
Function of slimy capsule that some bacteria have outside their cell wall
- Prevents detection by host immune cells
- Keeps cells from drying out
- Sometimes help with adhesion to other cells
- Mostly made of polysaccharides
Steps of cell fractionation
- Break cells open through homogenization; amphipathic cells could do this
- Separate homogenate using centrifugation; organelles with greatest density would fall first (nuclei first)
Nucleus in DNA
- Stores DNA
- Site of DNA replication, transcription, ribosome assembly
How is DNA packed in the nucleus?
Chromatin+chromosomes (compacted chromatin)
Chromatin
DNA and the histone proteins it wraps around
Where is DNA stored in prokaryotes
Nucleoid
Where does transcription and translation occur in prokaryotes
In cytoplasm (happens at the same time and place)
Mitosis
Process of nuclear division in eukaryotic cells
How did nucleus form
Through invagination of the cell membrane
Mitochondria
- Powerhouse of cell
- Uses glucose to produce ATP
- Next dense organelle after nucleus
- Many layers of membrane
- Has own DNA and can divide separately from cell division but can’t divide or grow outside cell
Which cells have the most mitochondria
Cells that require a lot of ATP (e.g muscle cells)
Endosymbiotic Theory
Some eukaryotic organelles are a result of our ancestors engulfing from ancient bacteria
Chloroplasts
- Helps provide plants cells with energy
- Has own DNA and can divide separately from cell division but can’t grow outside of cell
Plant Vacuoles
May provide structure, hold pigment, aid in digestion, and/or store water or waste
Thylakoids
Located in the inner membrane of the chloroplast; harvests light for photosynthesis
Endoplasmic Reticulum
Where some new proteins are made, modified, and sent off to specific locations
Immunofluorescence
One technique for finding locations and relative abundance of specific proteins; allows us to see multiple cell structures at the same time
Cytoskeleton
The dynamic network of varied proteins that gives cell structure and facilitates movement
Roles of the cytoskeleton
- Supports and maintains cell shape
- Holds organelles in position
- Moves organelles
- Involved in cytoplasmic streaming
- Interacts with extracellular structures to hold cell in place
Microfilaments
One of the three filaments that make up the cytoskeleton; long chains of the monomer actin
Roles of microfilaments
- Maintain cell shape by resisting tension (pull)
- Move cells via muscle contraction or crawling
- Divide animal cells in two
- Moves organelles and cytoplasm in plants, fungi, and animals
- Has distinct plus/minus ends
How do microfilaments move?
Via cytoplasmic streaming; actin and the motor protein myosin interact to cause movement; myosin head attaches to actin and uses ATP to move, causing filament to slide
Intermediate filaments
One of the three filaments that make up the cytoskeleton; tough rope-like structures that maintain cell shape by resisting tension and anchor cell structures (nuclei) in place (many different compositions like keratin)
Microtubules
One of the three filaments that make up the cytoskeleton; long hollow cylinders (polymers) made of dimers of the a and b tubulin
Roles of microtubules
- Forms a rigid internal skeleton
- Maintains cell shape by resisting cell tension (push)
- Can change length rapidly by adding or losing dimers at plus or minus ends
- Acts as train tracks for motor proteins; moves cells via flagella or cilia and moves chromosomes during cell division
What are eukaryotic flagella and cilium made of
Microtubules in “9+2” array called an axoneme
Kinesin
The motor protein that uses ATP to move cargo along a microtubule
What bonds to microtubule doublets and allows cilia and flagella to slide past each other to facilitate movement
Dynein
Evolution of mitochondria/ chloroplasts in a eukaryotic cell probably occurred through endosymbiosis, but that of nucleus/ ER/ Golgi was likely through
Nuclear Envelope
Comprised of 2 layers of protein studded membrane that protects the DNA in the nucleus and regulates entry and exit of other molecules
Endoplasmic Reticulum
Network of tubes where some proteins are made, modified, packaged, and sent to specific locations
Where are ribosomal proteins synthesized
RER; Proteins made in the RER are destined to become embedded in the membrane, end up in the lysosome, or leave the cell
Does the smooth ER contain ribosomes
No
Smooth Endoplasmic Reticulum
Another site of protein modifications but has other functions including
- Chemically modifying small molecules such as drugs
- Site of glycogen degradation in animal cells
- Synthesis of lipids and steroids
- Stores calcium ions
What are all new proteins routed through
ER and Golgi (secretory pathway)
What do proteins leave the ER in to go to the Golgi Apparatus
COPII-coated transport vesicles
What happens to proteins in the Golgi Apparatus
They’re further modified, packaged, and sorted
Order that cargo travels in vesicles in secretory pathway in Golgi
cis –> medial –> trans; from there could end up in lysosome, membrane, or outside cell
The endomembrane system is an interconnected system of membrane-enclosed compartments including
Nuclear envelope, ER, golgi apparatus, lysosomes, and cell membrane
Fluid Mosaic Model
Describes membrane structure; phospholipids form a liquidy bilayer which is like a lake in which some proteins float
How does fatty acid saturation affect membrane fluidity
Saturated (straight) = Rigid
Unsaturated = Fluid
How does fatty acid chain length affected membrane fluidity
Long = Rigid
Short = Fluid
How does cholesterol/lipid composition affect membrane in fluidity in animal cells
Low = Fluid
High = Rigid (more van der waals forces)
How does temperature affect membrane fluidity
Low (low kinetic energy) = Rigid
High = Fluid
What does a rigid membrane mean for permeability of a cell
More rigid = less permeability
What are biological membranes comprised of
Phospholipids and proteins
Steps for protein co-translation into the RER membrane
- ER signal sequence is synthesized by ribosome
- ER signal sequence binds to signal recognition particle (SRP) and halts synthesis
- SRP binds to receptor in ER membrane
- SRP is released; protein synthesis continues; protein enters ER through the translocon
- ER signal sequence is removed; protein synthesis then proceeds to completion
Glycosylation of a protein
Occurs in RER by glycosyltransferase protein; essential for a proteins folding/function, stability, cell-cell communication, and transport
What determines where a protein goes after they leave the trans face of the Golgi in their vesicles?
Proteins carry tags in the endomembrane system that serve as zip codes for different destinations
ER Signal Peptides
Example of zip code for protein targeting; stops translation until docked at ER; detected by SRP during translation; detected co-translationally
KDEL
Example of zip code for protein targeting; tells protein to stay in the ER lumen
Nuclear Localization Sequence
Example of zip code for protein targeting
Peroxisomal Targeting Signal
Example of zip code for protein targeting
Mannose-6-Phosphate
Example of zip code for protein targeting; tells protein to go to the lysosome
Integral Membrane Proteins
One of the three types of membrane proteins; at least partially embedded in the bilayer; some are transmembrane and extend all the way through the bilayer
Anchored Membrane Proteins
One of the three types of membrane proteins; covalently attached to fatty acids or other lipids inside the membrane
Peripheral Membrane Proteins
One of the three types of membrane proteins; lacks exposed hydrophobic regions, are noncovalently attached to the membrane and don’t penetrate the bilayer
Homotypic Cell Adhesion
The same molecule sticks out from both cells and binds to each other (less common)
Heterotypic Cell Adhesion
The cells have different proteins that bind together (more common)
Cell Junctions
Specialized structures comprised of many different proteins that hold cells together
Tight Cell Junctions
Forms a tight seal (barrier) between cells, which helps ensure directional movement of materials
Gap Cell Junctions
Forms tunnels called channels so that adjacent cells can communicate by exchanging small molecules, electrical impulses, etc
Desmosome Cell Junction
Holds cells together like velcro; also allows materials to move around in the intercellular space
Cells can move within a tissue by the binding and reattaching of adhesion receptors to the
Extracellular matrix
Integrals
One type of adhesion receptor that can facilitate movement through binding/reattaching to extracellular matrix
Extracellular Matrix
Macromolecule-rich gel outside of cells
Diffusion
Process of random movement of solute from a region of higher to lower concentration
Diffusion works better over
Short Distances
Molecules move across permeable membrane in diffusion until
Concentration is equal on both sides
What factors affect the rate at which substances diffuse
- Concentration gradient
- Size and mass of particles
- Temperature of solution
- Density of solution
- Area and distance
Osmosis
Process by which water diffuses across membrane
Isotonic
Equal solute concentration inside and outside cell
Hypotonic
Lower solute concentration outside of cell
Hypertonic
Higher solute concentration outside cell
Passive Transport
Process by which substances can cross membranes without energy input
Aquaporins
Channels made of transmembrane tunnels made of protein through which water moves across membrane (example of facilitated diffusion)
Facilitated Diffusion
Carried out by protein channels or carriers that increase the ……
Ion Channels
Penetrate the membrane and have hydrophilic pores (facilitated diffusion)
What stimulates the protein of an ion channel to open
- A chemical signal (ligand)
- An electrical charge (voltage gated)
- A mechanical signal (force)
Carrier Protein
Transports specific polar molecules, like glucose, across membrane in both direction (facilitated diffusion)
What is it called when glucose transporters are all occupied
Saturated
Active Transport
Requires energy; movement against concentration gradient
Three kinds of proteins that active transport involves
- Uniporter: One molecule in one direction
- Symporter: Two in one direction
- Antiporter: Two in different directions
Primary Active Transport
Requires direct hydrolysis of ATP (ex: sodium-potassium pump)
Secondary Active Transport
Energy comes from an ion concentration gradient that is established by primary active transport
Endocytosis
Process where eukaryotic cells may take up and release fluids, large molecules, particles, and smaller cells (way that larger molecules can cross membrane)
Phagocytosis
Type of endocytosis; molecules/entire cells are engulfed; a food vacuole or phagosome forms, which fuses with a lysosome where the contents are digested
Pinocytosis
Type of endocytosis; vesicle forms to bring small dissolved substances or fluids into a cell; vesicles are much smaller than in phagocytosis
Receptor-Mediated Endocytosis
Type of endocytosis; uses proteins
How do cells process info from the environment
A ligand binds to a receptor in a specific binding site; cells must have a specific receptor molecule that can detect it
How do chemical signals differ in their source and distribution (mode of delivery)
- Autocrine Signaling: On same cell
- Juxtacrine: Not far, touching cells
- Paracrine: Across extracellular space
Hormones
Travels to distant cells via the circulatory system; circulating signals are transported by the circulatory system
Signal Transduction Pathway
A signal from outside the cell is relayed through a series of internal messengers that can cause short or long term changes in the cell
Short terms changes from signal transduction pathways
Enzyme activation, cell movement
Long term changes from signal transduction pathways
Altered DNA transcription
Agnonists
Type of drug; has the same effect as ligand when binding to a receptor
Antagonists (inhibitors)
Type of drug; prevents ligand from binding but doesn’t trigger a response when binding to receptor
Ion Channel Linked Receptor
Type of eukaryotic membrane receptor; allows ions to enter or leave a cell; signal binding results in change in shape of the channel protein, and the channel opens
Protein Kinase Receptors
Type of eukaryotic membrane receptor; When ligand is present at the extracellular ligand binding domain, PKR catalyzes phosphorylation of themselves and/or other proteins to change their shapes/functions
What does phosphorylation of a protein do?
- Changes shape of protein
- Alters its catalytic activity
- Affects its activity with other proteins
G Protein Coupled Receptor
Type of eukaryotic membrane receptor; activates a special protein called a G protein, which then activates an effector
When are G proteins active
When connected to a GTP; not GDP
Intracellular Receptors
Responds to signals such as light or small molecules that can cross the cell membrane; many are transcription factors, which alter gene expression
What are the three amino acids that can be phosphorylated by protein kinase activity
Serine, threonine, and tyrosine
In a protein kinase cascade
- The signal is amplified at each step
- Info that arrived at the cell membrane is communicated to the nucleus
- Different target proteins provide variation in the response
Cyclic AMP (cAMP)
A 2nd messenger that amplifies and distributes a signal
Second Messengers
Nonprotein signaling molecule that increase in concentration inside a cell in response to a signaling molecules that binds at the surface
How is Protein Kinase A activated
By a high concentration of cAMP
Epinephrine (adrenaline)
Mediates the fight or flight response
IP3 and DAG
Second messengers made from hydrolysis of PIP2 by phospholipase C
CA2+ Channel role
IP3 binds to and activates a CA2+ channel in the ER membrane; the activated CA2+ channel releases stores of CA2+ from ER; the increased CA2+ helps activate protein kinase C; with CA2+ bound, PKC binds and becomes fully activated by DAG; activated PKC phosphorylates other proteins to stimulate a cellular response
How do cells respond to signals
- Opening ion channels
- Changing enzyme activity
- Differential gene expression
NO Gas
A 2nd messenger between acetylcholine and the relaxation of smooth muscle in blood vessels, allowing more blood to flow
What determines the cellular response to a signal
The balance between enzymes that activate and enzymes that inactivate transducers
How are signal transduction pathways turned off/regulated
- Kinases can be inactivated by phosphatase enzymes which removes phosphate groups
- GTPases inactivate G proteins by hydrolyzing GTP (becomes GDP)
- 2nd messengers can be broken down (ex: phosphodiesterases degrade cAMP to AMP or cGMP to GMP)
