Cell Biology Flashcards
Magnification Equation
Size of image over actual size
Four differences between theories and laws
- Theories provide the most logical explanation for what happens while laws explain what happens
- Theories can be proposed, challenged, revised while laws resist change
- Multiple theories compete to best explain a phenomenon while there is only a single law for a single phenomenon
- Theories need to be proven and are subject to tests while laws don’t need to be proven
7 Criteria of Life
- Metabolism
- Homeostasis
- Nutrition
- Excretion
- Sensitivity
- Reproduction
- Growth
Cell Theory
- The cell is the smallest unit of life
- All living things are made of cells
- Cells come form pre-existing cells
Three Exceptions to Cell Theory
- The striated muscle: cells have multiple nuclei, challenges that which makes up a cell
- Aseptate fungi: without septa (cell walls), one cell with several nucleii
- Giant algae: the foot, step and cap considered to be a single cell: is the cell the smallest unit of life?
Why do cells divide instead of keep growing larger and larger?
If the cell’s surace area becomes too small compared to the volume, the cell memrbane won’t be able to transport nutrients inside the cell fast enough to support the whole cell, nor will it be able to expel waste fast enough to make space for everything else
Nine Differences: Prokaryotes and Eukaryotes
Prokaryotes are…
1. Small and simple
2. Have no nucleus (nucleoid region)
3. No membrane bound organelles
4. Unicellular but may form colonies
5. One circular chromosome
6. DNA is circular
7. Mainly asexual reproduction
8. Many are anaerobic
9. 70s ribosomes
Eukaryotes are…
1. Larger and more complex
2. Have a nucleus
3. Membrane bound organelles
4. Multicellular
5. More than one chromosome
6. DNA is linear
7. Mainly sexual reproduction
8. Mainly aerobic
9. 80s ribosomes
Bacteria are too small to be seen with a …
Light microscope
Bacteriophage
Viruses that specifically target and kill bacteria
Phage therapy
Modifying viruses to attack bacteria
The nucleoid region isn’t called the nucleus because…
It’s not membrane bound
Prokaryotic pili
Attach to things and communicate with other cells and for bacterial conjugation.
Bacterial flagella
Allow for movement
Prokaryotic plasmid
Separate piece of DNA
Binary Fission vs. Mitosis
Bacteria cannot undergo mitosis because they don’t have nucleii
Two advantages of binary fission
- Can be done over and over again
- Fast and efficient
4 ways in which genetic diversity is created by bacteria
- Genetic mutations
- Errors that occur during the course of evolution
- Bacteria can swap plasmids with different species
- Plasmid gets copied alongside the DNA
Process of Plasmid Sharing (4 Steps)
- A factor triggers a bacterium to extend its conjugation pilus
- The pilus extends then pulls F- closer
- F+ donates the plasmid
- F- receives the plasmid
Two Possibilities during Plasmid Sharing
- The F- extends its own pilus and send plasmid back
- 2 bacteria exchange genetic information
Eukaryotic ribosomes
Have two subunits, one large and one small. SIze: 80s (Svedberg unit)
Endoplasmic Reticulum
Double layered, connected to the nucleus
Rough ER
Protein synthesis and modification
Smooth ER
Lipid synthesis
Golgi Apparatus
Made from membrane, fused together to make the cell membrane. Transports protein out of the cell
Vesicle
Any membrane bound organelle
Mitochondrion
Conducts cellular respiration, double membraned
Peroxisome
Breaks things down
Microtubule
Internal support system, maintains the shape of the cell
Cytoplasm
Everything inside the cell except for the nucleus
Cytosol
The jelly like substance suspending all the organelles mid - aor
Endosymbiotic Theory
Eukaroytic cells theorized to have evolved from early prokaryotes that were engulfed through phagocytosis. The engulfed cell remained undigested as it contributed new functions to the larger cell, forming an endosymbiont. Over time the engulfed cell evolved to become an organelle, as the cell provides it with nutrients and it with cellular respiration/photosynthesis
Endosymbiont
Mitochondrium, chloroplast. Possesses its own cell membrane, contains its own set of DNA and ribosomes, similar to bacteria in size.
Two Functions of the Cell Membrane
- Separate and dinstinguish a cell from its surroundings
- To allow certain substances in and out to supplt the cell with needed nutrients and to expel waste
Two Cell Membrane Models
Davson - Danielli (two protein layers sandwhiching tow phospholipid layers) and Singer and Nicholson (proteins are embedded within the bilayer)
Two Types of Proteins in the Singer and Nicholson Model
Both types are mobile
1. Integral: embedded within the membrane
2. Peripheral: attached to the inner (fatty acid chains) or outer surface
Three Proofs of the Singer Nicolson Model
- Freeze - etched electron micrograph: cell is frozen in liquid nitrogen, cleaved along the bilayer’s fracture plane: proteins were found to be embedded
- Structure of the membrane proteins: extracted and observed to be globular in shape; they are less likely to gorm continuous layers than fibrous proteins
- Fluorescent antibody tagging: two cells with red and green markers attached to antibodies binding to membrane proteins were fused; both colors spread throughout the cell
Structure of the Cell Membrane
Phospholipids, cholesterol and proteins
Structure of Phospholipids
The hydrophilic components: the phosphate group and glyverol molecule.
The hydrophobic component: fatty acid tails
Properties of Phospholipids
Amphipathic: prevent random materials from entering or leaving the cell and allows the membrane to spontaneously form a bilayer
Hydrophobic tail regions face x while hydrophilic head region associate with the y and z environments
X: inwards
Y: Cytosolic
Z: Extracellular
Phospholipid Movement Types
- Lateral (swap places with a phospholipid beside it)
- Flip - flop: swap places with a phospholipid on the layer opposite it)
Role of Cholesterol in Cell Membrane
Regulates membrane fluidity. At warmer temperatures, cholesterol restraints movement of the phospholipids; at colder temperatures, it increases movement
Transmembrane integral proteins
Stretch across the entirety of the phospholipid layers
5 Functions of the Proteins in Cell Membranes
- Intercellular joinings and anchorage
- Enzymatic activity
- Transport
- Cell - cell recognition
- Signal transduction
Fluidity created by the Phospholipid Bilayer allows for the…
Breaking and remaking of membranes during exocytosis and endocytosis
Three Main Goals of Intramembrane Transport
- Take in nutrients
- Expel waste
- Keep the internal environment within certain parameters (homeostasis)
Passive transport is driven by x and requires no y
X: Diffusion: the tendency of molecules within a closed space to spread out evenly among it
Y: Expenditure of cellular energy
Factors Affecting Diffusion
- Concentration gradient
- Size of particles
- Temperature
The concentration gradient is always naturally…
From high to low concentration
Dynamic Equilibrium
No net movement: the amount of particles traveling in either direction is equal
Osmosis
Diffusion of water across a selectively permeable membrane
Tonicity
The ability of a solution to cause a cell to gain or lose water
Hypotonic Solution
Cell gains water, becoming lysed
Isotonic Solution
No net water movement across the membrane
Hypertonic Solution
Cell loses water, becomes shriveled
Plant cells require more x than animal cells
X: water
Plant cells are x in a hypotonic solution, y in an isotonic solution, z in a hypertonic solution
X: turgid (normal)
Y: flaccid
Z: plasmolyzed
Only x and Y can cross the cellular membrane through diffusion
Small hydrophobic molecules and uncharged polar molecules
Facilitated diffusion is passive or active?
Passive
Facilitated Diffusion Mechanism
Transport proteins allow passage of hydrophilic substances across the membrane
Channel proteins are hydrophilic or hydrophobic?
Hydrophilic
An example of a channel protein
Aquaporin
Carrier Proteins Mechanism
Bind to molecules, then undergo conformational change and shuttle them across the membrane. Specific to the type of molecule it binds to
Active transport is the result of the cell’s need to…
Gain more control over its internal environment
Active transport requires energy in the form of…
ATP
Energy for primary active transport comes from…
The direct hydrolysis of ATP
Secondary Active Transport
Indirectly coupling transport with another molecule moving along its gradient
The Sodium Potassium Pump
A form of secondary active transport
1. Three Na ions bind to intracellular sites on the pump
2. A phosphate group is transferred to the pump through hydrolysis
3. The pump undergoes conformational change as it translocates Na across the membrane
4. 2 K binding sites are exposed outside
5. A catalyzed reaction releases the phosphate group, causing the pump to return to its original conformation
6. The potassium is pumped through the membrane
Proton Pump
Relies on an electrochemical gradient, also uses ATP to pump hydrogen ions from the negatively charged cytoplasm to the positively charged extracellular fluid
Co - Transport Types
Symport (same direction) and antiport (opposite directions)
Bulk Transport
For large molecules that need to travel in bulk through vesicles, which are moved by microtubules
2 Types of Bulk Transport
Endocytosis and Exocytosis
Endocytosis
The cell takes in a macromolecule by forming vesicles form the plasma membrane
Phagocytosis
The cell engulfs a particle in a vacuole, which then fuses with a lysosome to digest the particle
Pinocytosis
Molecule are taken up in tiny vesicles alongside extracellular fluid
Receptor - mediated endocytosis
Binding of ligands, a molecule that binds specifically to a receptor site of another molecule to receptors triggers vesicle formation. Restricts the type of substances allowed inside
Exocytosis
Transport vesicles migrate to the membrane, fuse with it, then release the contents
Types of Stem Cells
- Totipotent: can form ANY cell type
- Pluripotent: Can form any type except for extra - embryonic tissue
- Induced pluripotent: pluripotent that comes from an adult stem cell
- Multipotent: can form closely related types
- Unipotent: cannot differentiate
Disadvantages of stem cell therapy
Possibility of tumors forming, the body rejecting the foreign cells
Stargardt’s Disease
Macular degeneration, causing progressive vision loss. Stem cells can replaced compromised photoreceptor cells
3 purposes of mitosis
Cell/organism growth, asexual reproduction, tissue repair
Three Stages of Interphase
- G1: occurs in the cytoplasm, involves regular processes, growth, rapid protein synthesis, replication of mitochondria and chloroplasts
- S: occurs in the nucleus, proteins made during G1 used for DNA synthesis and replication
- G2: occurs in the cytoplasm, protein synthesis for components used during mitosis, like spindle fibers
Prophase Summary
Chromosomes, spindle fibers and centrosomes form, membranes dissolve
Metaphase Summary
Chromosomes line up along the equator of the cell
Anaphase Summary
Spindle fibers attach to the centromeres of the chromosomes and pull apart the sister chromatids
Telophase Summary
Cleavage furrow forms, the nucleus and the nuclear membrane reform
Cytokinesis Summary
In animal cells: microfilaments constrict to form a cleavage furrow, which pinches the cell into two. In plant cells: carbohydrate rich vesicles around the center of the cell fuse, forming a plate
Cyclins
- A protein that regulates mitosis
- Undergoes a cycle of synthesis and decomposition during cell division
How Cyclin Regulates Mitosis
Cyclins accumulate during G2 of interphase. The mitosis promoting factor (MPF) forms, signaling the cell to enter mitosis. Once the cyclin degrades, the MPF is deactivated, signaling the cell to exit mitosis, dividing into two
Three Factors that Control Cyclin Levels
Cell size, completion of DNA replication and the cellular environment
Cyclin Dependent Kinase
Enzyme that adds phosphates to molecules, activated by cyclin
Activation of G1/S Cyclin
Cyclin activates CdK, which phosphorylates targets, beginning the S phase, activating DNA replication enzymes
Mitotic Index Equation
NUmber of cells in mitosis over total number of cells
Mitotic indices differ due to…
Different cells’ differing locations and functions
Mitotic Index Usage
Cancer diagnosis
Cancer Definition
Abnormally fast growth of cells caused by multiple gene expression changes. The rate at which cells are forming is faster than that which they are dying off.
Pasteur’s Experiment
- A growth medium was boiled to kill any microorganisms already present
- Placed the medium in different containers
- It was observed that bacterial growth only occurred in the medium if the flask was exposed to the air
- Proved that bacterial growth came from external contaminants and is incapable of self - generation
Abiogenesis Process (5 Steps)
- Simple organic molecules are formed
- The simple organic molecules form more complex polymers
- The polymers must have the ability to self - replicate
- The polymers are eventually cut off from the environment by the formation of a cell membrane around them
- The polymers develop a different internal chemistry from their surroundings by becoming protobionts
Urey Miller Experiment (5 Steps)
- Water is boiled to vapor to mimic the high temperatures present on Earth during primordial times
- The vapor is mixed with gases like hydrogen, methane and ammonia to create a reducing atmosphere, where oxygen is limtied
- The mixture is exposed to an electrical discharge to mimic the effects of lightning as an energy source
- The mixture is allowed to cool and left alone for about a week
- The mixture is analyzed after the week and found to contain traces of simple organic molecules like amino acids and carbohydrates
Since the conditions of primordial earth no longer exist, cells can no longer…
Undergo abiogenesis and can only come from pre - existing cells
