Cells Flashcards
Cell Theory
- Cells are the smallest units of life
- Organisms activities are determined by the activitiesof their cells
- Activities of cells are determined by their shape and number
- Contimuity of life depends on cells — Mitosis and Meiosis
Cell Diversity
There are many different types of cells
What do all cells have?
All cells have nuclei at some point
Nucleus
control center of the cell; contains DNA and RNA
Nuclear envalope
membrane of nucleus
nuclear pore
holes in nuclear envalope; allows DNA and RNA through
Nucleolus
center of nucleus; creates ribosomes
Chromatin
Packed DNA into smaller volume to fit in the cell
Smooth ER
makes lipids and phospholipids
Rough ER
Transports Proteins
Ribosomes
makes proteins
Golgi Apparatus
modifies, recieves and sends out proteins in vesicles
Mitochondria
Makes ATP
Cytoskeleton
supports and gives shape to a cell
Plasma Membrane
Selectively permiable; protects cell
Cytoplasm
Colloid; suspends organelles in cell
Centrioles
involved in mitosis
Lysosomes
breaks down old organelles; disposes of things
Steps to Protein Synthesis (Transcription and Translation)
- The first stage of protein synthesis is transcription. The DNA helix is untwisted by the enzyme dna helixase
- Then the DNA is split into two as the hydrogen bonds are broken between the complementary base pairs by RNA polymerase
- Then a mRNA strand is made with complementary pairs, much like with DNA replication. However this mRNA strand leaves the nucleus via the nuclear pores.
- The second step of protein synthesis is translation, which occurs in the cytoplasm and requires ribosomes. A small ribosomal subunit attaches to the bottom of the mRNA strand, and a large ribosomal subunit to the top of the mRNA
- Then the synthesis can begin. For it to start the first codon (base triplet) must be methionine (AUG.) Then the anticodons on a tRNA with an amino acid comes into the large ribosome unit and matches with a codon
- The first anticodon must be (UAC) because it is complementary to AUG. Then the next anticodon comes along.
- Before the tRNA leaves the ribosome polmerase creates a peptide bond between the amino acids
- Then the tRNA leaves the ribosome, leaving the amino acid behind.
- This process repeats itself until it reaches a stop codon
- Then the amino acid chain (polypeptide) is released into the cytoplasm as a protein when the ribosome and mRNA separate
- This protein is in its primary structure (the arrangement.) It can then assume its secondary structure (alpha helix or beta pleated sheet.) Then tertiary 3d precise shape (globular of fibrous.)
Name the parts of this membrane
A. Glycoprotein
B. Glycocalyx
C. Glucose
D. Non-Polar tails of phospholipids
E. Phospholipid bilayer
F. Polar heads of phospholipid
G. Periphrial portein
H. Cholesterol
I. Integral Proteins
J. Filament of cytoskeleton
(not seen here glycolipid)
What does the plasma membrane do?
it separates ICF fro ECF (intersitial fluid; full of ions, wastes, nutrients, hormones; which bathe the cell)
What combines in unique ways to form a cell?
The 4 macromolecules
What is the cytoskeleton made of?
proteins
what makes up the phospholipid bilayer?
Carbs, lipids and proteins
What is the plasma membrane made of?
–Phospholipids
–Glycolipids
–Cholesterol
–Proteins
Fluid mosaic model
Thin bi-layer of lipids and proteins that move around.
Types of membrane proteins
- Transport proteins
- Receptors for signal transduction
- Anchor proteins: attached to the cytoskeleton and extracellular matrix
- Enzamatic Activity
- Intercellular joining
- Cell to cell recognition
Transport proteins
can be a channel, may hydrolyze ATP to ransport substances into and out of the cell
Proteins that serve as receptors for signal transduction
Has an active site on its outer aspect which binds with a specific chemical (hormone) The binding causes the protein to change shape and initiate a chemical reaction in the cell.
Anchor proteins
May bind adjacent cells together, play a role in cell movement. cytoskeleton and extracellular matrix fibers anchor to protien to maintain cell shape and location.
Enzyme proteins
A membrane protein that catalyzes chemical reactions, by binding substrates with its active sites. Proteins next to eachother can complete different steps in a metabolic process.
Intercellular joining proteins
proteins of adjacent cells may be attached by different types of junctions.
Cell to cell recogniton proteins
glycoproteins serve a s identification tags so cells can recognize eachother.
Three ways groups of cells can be held togther…
- Gap Junctions
- Desmosomes
- Tight junctions
Tight junctions
- Has interlocking junctional proteins with intercellular space
- Impermiable junctions prevent molecules from passing through the intercellular space
- Tight junctions seal adjacent epithelial cells in a narrow band just beneath their apical surface.
Desmosomes
- Plaques with intermediate filaments on the inside of the cell, and linker proteins (cadherins) on the outside between the intercellular space.
- Anchoring junctions bind adjacent cells togther like a molecular velcro and help form an internal tension-reducing network of fibers.
- found in skin
Gap junctions
- Channels between cells in inter cellular space cormed by connexons
- Communicating junctions allows ions and small molecules to pass for intercellular communication
- found in cardiac muscle in the heart
Intersitial fluid
- contains nutrients, wastes, ions, and hormones
- bathes the cells
Why is membrane transport necessary?
•Transport is necessary to deliver nutrients/water/hormones to cells
What is special about the plasma membrane?
its selctively permeable, selective permeability is a characteristic of healthy cells.
What are the 2 types of membrane transport?
- Passive transport
- Active transport
What are the 2 types of passive transport?
- Filtration
- Diffusion
What are the types of diffusion?
- Simple diffusion
- Facilitated diffusion
- Osmosis
What are the types of facilitated diffusion?
- Carrier mediated facilitated diffusion
- Channel mediated facilitated diffusion
What is the definition of diffusion?
movement of ions or molecules from High to Low concentration moving down their concentration gradient
Definition of Osmosis
a process by which molecules of a solvent tend to pass through a semipermeable membrane from a less concentrated solution into a more concentrated one, thus equalizing the concentrations on each side of the membrane.
Is ATP needed for passive processes?
No
What molecules are let into the cell via simple diffusion?
- Oxygen
- CO2
- Fat soluable vitamins
Simple diffusion
- Fat soluable molecules go directly through phospholipid bilayer
What molecules are let into the cell via carrier mediated facilitated diffusion?
- Glucose
- other sugars
- Amino Acids
Carrier mediated facilitated diffusion
- Molecules are let in via protein carrier specific for one chemical; binding of a substrate causes carrier protein to change shape.
What molecules are let into the cell via channel mediated facilitated diffusion?
- Water
- Molecules
Channel mediated facilitated diffusion
- molecules enter through a channel protein; mostly ions selected on basis of size and charge
- Channels can be leaky or gated
Osmosis (A type of diffusion specific to water)
- diffusion of a solvent such as water through a specific channel protein (aquaporin) or through he lipid bilayer
Definition of osmolarity
•Total concentration of all solutes particles in a solution (this can be the inside of a cell!)
Definition of Tonicity
- the ability of a solution to change the shape or “tone” of the cells by changing their internal water volume
Types of solutions
- Isotonic solutions
- Hypotonic solutions
- Hypertonic solutions
Hypertonic solutions can be infused (via IV) into patients with severe edema
Why?
- To counter act the hypotonic solution and cause the cells to give up the extra water
_______ of a cell can change because the ______ changed
- Tonicity
- Osmolarity
Homeostasis starts at the level of the _______.
- Cell
Membrane transport: Active processes
- Requires carrier proteins to bind specifically and reversibly with the solutes they transport
- Solutes are moved against their concentration gradient
[High] ——> [Low]
- down the concentration gradient
[Low] ——-> [High]
Against the concentration gradient
Active Transport is also known as _______.
- Solute pumping
Active transport requires ________.
- ATP
What are the 2 types of active transport?
- o 1 active (primary) transport
- o2 active (secondary) transport
o 1 Active transport
- Primary active transport: energy comes directly from Hydrolysis of ATP
- •Examples are
–Hydrogen pumps
–Calcium pumps
–Naᶧ/Kᶧ pumps
- They only move one substance at a time (move Na+ then K+)
•In the body [Kᶧ] is ____ times higher inside the cell, the reverse is true for [____] .
- 10x
- [Na+]
Ionic concentration differences are essential for cells that are excitable (i.e.______________)to function normally
- Cardiac muscle cells
- Nuerons
Na+/K+ pump AKA…
- Na+/K+ ATPase; the pump is an enzyme
The Na+/K+ pump is also….
•Important for other cells to maintain normal fluid volume
•Ions create an ________________ (accounts for both electrical and concentration forces)
- electrochemical gradient
Electrochemical gradient
An electrochemical gradient is a gradient of electrochemical potential, usually for an ion that can move across a membrane. Thegradient consists of two parts, the electrical potential and a difference in the chemical concentration across a membrane.
- Na+/K+ pump maintains electrochemical gradient across the cell
How the Na+/K+ pump works
- 3 Cytoplasmic Na+ bind to the sodium potassium pump
- Na+ binding stimulates hydrolysis of ATP
- Phosphorylation causes the protein to change its conformation, expelling Na+ to the outside
- 2 Extracellular K+ bind to the protein, triggering release of the phosphate group
- Loss of the phosphate restores the protein’s original conformation
- K+ is released and Na+ sites are receptive again; the cycle repeats
in the Na+/K+ pump how many Na+ and how many K+ are pumped?
- 3 sodiums for every 2 potassiums
The Na+/K+ pump is considered active transport because…
- You are going against the concentration gradient from low to high which requires extra energy
o2 Active transport
Moves substances indirectly using the energy stored in the ionic gradients created by primary active transport pumps
- No hydrolysis of ATP
Primary transport helps secondary transport to occur! HOW??
–Na⁺ moves back into the cell (down its gradient) and “drags” other molecules with it using a common transporter protein using stored energy in the ion gradients
How many things are moved at one time in secondary active transport?
- 2 things at a time
Examples of things moved with secondary transport in the body.
sugars/amino acids and ions move with 2° transport in the intestines
secondary active traansport is common in what type of cells
- Non excitable cells
Do leak channels undo differences in the ionic gradient?
No
Another form of transportation in and out of the cell.
Vesicular Transport
Vesicular transport…
Uses membranous sacs to move large particles and macromolecules into and out of cells by hydrolyzing ATP
Endocytosis
Vesicular transport moves substances into cells
Exocytosis
uses vesicals to move substances out of cells
Types of endocytosis
- Phagocytosis: “eating cell action” ex. Macrophages
- Pinocytosis: “drinking cell action” ex. Epilthelial cells in capillaries
- Receptor- mediated endocytosis; concentrating things into the cell ex. Enzymes, hormones, iron, viruses.. This is done to limit the amt. according to need.
Exocytosis
- Stimulated by cell-surface signals (hormone or change in voltage)
- –Hormone secretion
–Neurotransmitter release
–Mucus secretion
What is Resting Membrane potential?
- Literally, a voltage exists across a plasma membrane in a cell
What’s a voltage?
- Difference in energy potential between 2 points
- The inside and outside of the cell are oppositely charged
- Results fron the concentration of oppositely charged particles on both sides
What are the charged particles that cause the a voltage to exist across the plasma membrane? and what is keeping them apart?
- Na+
- K+
- The membrane keeps the (ions) charges apart
ALL BODY CELLS (at rest) have a membrane potential between….
- -50 to -100 mV (depends on cell)
Why have a – (negative) sign when refering to the mV of a cell’s resting potential?
- The negative refers to the inside of the cell being more negatively charged than the outside.
All cells are “polarized” ….
charge separation occurs only at the membrane
What keeps/maintains this polarization at the membrane?
- Largely due to K⁺ ions
- Because if you are losing potassium ions to the outside the inside will be negative
Anions
- Negatively charged proteins in cell
potassium leaves through…
K+ leak channels leaving anion proteins behind making the inside of the cell negative. because it wants to go to where there is low concentration.
When an excitable cell is excited the membrane potential will be…
- Reversed; action potential
- ex. excited neuron
why does resting membrane potential matter?
- Resting membrane is necessary for action potentials to happen; the separation of charges hold potential energy that is activated during an action potential.
What cells use pinocytosis and why?
- Epithelial cells in capillaries use pinocytosis to engulf the liquid portion of blood at the capillary surface. The resulting vesicles travel across the capillary cells and release their contents to surrounding tissues, whileblood cells remain in the blood.
What cells use transcytosis?
- Epithelial cells use transcytosis for immune defense, nutrient absorption, and plasma membrane biogenesis. Other cell types employ transcytosis as well, such as the endothelium and the endocrine system
definition of resting membrane potential
- Resting Membrane Potential (RMP) is the voltage (charge) difference across the cell membrane when the cell is at rest. Outside. 0. PotentialDifference Across. A Membrane.
what cells depend on resting membrane potential?
- excitable cells; neurons
What is the voltage for resting membrane potential?
- -70 mV
What keeps the charges of the on ether side of the cell separate?
- The cell membrane
what is an electrochemical gradient? What does it depend on?
- An electrochemical gradient is the combined difference in concentration and charge; influencesthe distribution and direction of diffusion of ions. Electrochemical gradients depend on Na+/K+ ATPase to establish the concentration of ions inside and outside the cell membrane.
