Exam 2 : Lecture Flashcards
Microscopy
Using microscope to view small-scale structures, staining techniques provide contrast
How Are Cells Studied?
Light Microscope (LM) : produces two-dimensional image and passes light through specimen
Electron Microscope (EM) : beam of electrons eliminates specimen and has a greater magnification and resolution than light light microscope
Two Types of EM:
Transmission Electron Microscope (TEM) - directs electron beam through thin-cut sections and gets 2D images
Scanning Electron Microscope (SEM) - directs an electron beam across surface of specimen and get 3D images
Cells Size and Shape
Cells vary greatly in size and shape
- erythrocyte (red blood cell containing hemoglobin ; a biconcave disc w/o nucleus) between 7 to 8 m
- oocyte (cell in ovary that may undergo meiotic division to form ovum ; eggs has a diameter of 120 um
Most cells are microscopic and shapes may vary from : spherical, cubelike, columnlike, cylindrical, disc-shaped, or irregular
The Range of Cell Sizes
Unaided Eye : human height, some muscle and nerve cells, ostrich egg
Light Microscope : human oocyte, most plant and animal cells (average 30 um), red blood cell, mitochondrion, most bacteria
Electron Microscope : viruses, ribosomes large macromolecules (proteins), small molecules (amino acids), atom
The Variety of Cell Shapes
Irregular-shaped : Nerve Cells
Biconcave disc : Red Blood Cells
Cube-shaped: Kidney Tubule Cells
Column-shaped : Intestinal lining cells
Spherical : Cartilage Cells
Cylindrical : Skeletal Muscle Cells
Three Main Structural Features of A Cell
Plasma Membrane - forms outer layer , barrier separating internal contents from external environment
(Modified extensions of plasma membrane - cilia flagellum, microvilli)
Nucleus - largest structure in cell enclosed by a nuclear envelope, contains genetic material (DNA), nucleolus, nucleoplasm (inner fluid)
Cytoplasm - cellular contents between plasma membrane and nucleus
(Includes : cytosol, organelles and inclusions)
Cytoplasmic Components (Cytosol, Organelles - membrane bound and non membrane bound, Inclusions)
Cytosol - intracellular/viscous fluid of cytoplasm, high water content and contains dissolved macromolecules and ions
Organelles - complex, organized structures within cells, unique shapes and functions
Two Categories
Membrane bound organelles - enclosed by a membrane, separates contents from cytosol, includes ER, golgi aparatus, lysosomes, peroxisomes, mitochondra
Non-membrane bound organelles - not enclosed within a embrane, composed of protein, includes ribosomes, cytoskeleton, centrosome, proteasomes
Inclusions - cytosol stores temporarily, not considered organelles, molecules added to and removed from continuously, ex: pigments, glycogen, triglycerides
Structure of A Cell
General Functions Cells Perform
Maintain integrity and shape of a cell - dependent on plasma membrane and internal contents
Obtain nutrients and form chemical building blocks - harvest energy for survival
Dispose of wastes - avoid accumulation that could disrupt cellular activities
Some are capable of Cell Division - help maintain tissue by providing cells for new growth and replacing dead cells
What is the advantage of using a TEM instead of an LM to study intracellular structure?
TEM provides greater magnification and resolution than LM allowing for more details to e seen
Which cell is larger, an erythrocyte or a human oocyte? What are their respective sizes?
Human oocyte : 120um , while red blood cell (erythrocyte) is 7-8 um
Diagram the three main components of the cell and label the plasma membrane, nucleus, and cytoplasm.
What cellular structure is responsible for forming the boundary of a cell and maintaining its integrity?
Plasma Membrane
Lipid Components of Plasma Membrane
Fluid mixture composed of equal parts lipid and protein by weight
Regulates movement of most substances in and out of cell
Contains : phospholipids, cholesterol, glycolipids
Lipid Components (Phospholipids, Cholesterol, Glycolipids)
Phospholipids - balloon with two tails; polar head and nonpolar tails hydrophobic tails form internal environment of membrane and hydrophilic heads directed outward
(Phospholipid bilayer is the basic structure of the framework - ensures cytosol remains inside the cells and interstitial fluid remains outside
Cholesterol - four ringed lipid molecule scattered within phospholipid bilayer, it strengthens and stabilizes the membrane against temperature extremes
Glycolipids - lipids with attached carbohydrate groups, located on outer phospholipid layer only, helps form glycocalyx (sugar coat) ; glycolipid + carbohydrate = glycocalyx
Structure and Function of the Plasma Membrane
Functional Categories of Proteins (6 Major Roles Played by Membrane Proteins)
Transport proteins - regulate movement of substances across membrane, ex: carrier proteins, channels, pumps, symporters and antiporters
Cell Surface Receptors - bind molecules called ligands, ex: neurotransmitters released from a nerve cell that binds to a muscle cell to initiate contraction
Identity Markers - Communicate to other cells that they belong to the body, are used to distinguish healthy cells from cells to be destroyed
Enzymes - catalyze (causes) chemical reactions, may be attached to either internal or external surface of a cell
Anchoring Sites - secure cytoskeleton to plasma membrane
Cell Adhesion Proteins - perform cell to cell attachments
Membrane Transport (2 Categories)
Process of obtaining and eliminating substance across the plasma membrane
Two Categories :
Passive Processes - do not require energy, depend on substance moving down concentration gradient (from area of more substance to area of less)
2 Types : Diffusion and Osmosis
Active Processes - require energy, substance must be moved up/against its concentration gradient (from less to more), membrane-bound vesicle must be released vesicular transport)
Passive Processes : Diffusion (Simple and Facilitated Diffusion)
Net movement of ions or molecules from area of greater concentration to area of less concentration (down the concentration gradient)
Due to Kinetic Energy (energy of motion) of ios/molecules - influenced by temperature and steepness, steeper gradient causes faster rate of diffusion, increased in temperature increased kinetic energy and rate of diffusion
If unopposed, diffusion continues until substance reaches equilibrium - molecules evenly distributed throughout a given area
Simple Diffusion
Molecules move unassisted between phospholipid molecules, small and nonpolar solutes, not regulated by plasma membrane, movement dependent on concentration gradient, continues to move as long as gradient exists
Includes ethanol urea, respiratory gasses (O2, CO2), some fatty acids
Facilitated Diffusion
Transport process for small charged or polar solutes requires assistance from plasma membrane proteins
Two Types:
Channel-mediated Diffusion - movement of small ions through water-filled protein channels, channels specific for one ion type, important in normal function of muscle and nerve cells
Leak Channels - continuously open
Gated Channel - usually closed, opens in response to stimulus for fraction of second
Carrier-mediated Diffusion - small polar molecules assisted across membrane by carrier protein, binding of substance causing change in carrier protein shape, releases substances on other side of membrane, moves substances down their gradient
Uniporter - carrier transporting only one substance
The number of channels and carriers determines the max rate of substance transport
Passsive Processes : Osmosis
Passive movement of water through Semipermeable Membrane - membrane allows passage of water, prevents passage of most solutes, it is also selectively permeable meaning it regulates movement of specific solutes
Osmosis is promoted by difference in water concentration on either side of a membrane
Two ways water crosses membrane :
Slips between molecules of phospholipid bilayer or moves through integral protein water channels (aquaporins)
Two types of Solutes :
Permeable - pass through bilayer, ex: small and nonpolar solutes O2, CO2, urea
Nonpermeable - prevented from passing through bilayer, ex: charged, polar, or large solutes such as ions, glucose proteins
Between cytosol and interstitial fluid - solutes are prevented from moving across the bilayer
Movement of water by Osmosis is dependent upon concentration gradient between cytosol and solution surrounding the cell
Water moves down gradient until equilibrium is reached.
Osmotic Pressure
Pressure exerted by movement of water across semipermeable membrane
Hydrostatic Pressure - pressure exerted by a fluid on the inside wall of its container
Osmosis and Tonicity
Cells gains or loses water, change in cell volume and osmotic pressure with osmosis
Tonicity is the ability of a solution to change the volume or pressure of a cell by osmosis
3 Relative Concentration of Solutions :
Isotonic - both cytosol and solution are the same, no net movement of water
Hypotonic - solution has a lower concentration of solutes, higher concentration of water than in cytosol (ex: erythrocytes in pure water), water moves down concentration gradient from outside to inside increases volume and pressure of cell
Lysis - rupturing of red blood cells occurs if difference is large enough
Hemolysis - rupturing erythrocytes
Hypertonic - solution with higher concentration of solutes than cytosol (ex: erythrocytes in 3% NaCl water solution, water moves down concentration gradient, decreases volume and pressure of cell
Crenation - cell shrinks
Active Processes (Ion Pumps, Sodium-Potassium Pump
Ion pumps - cellular protein pumps that move ions across membrane, maintain internal concentrations of ions
ex: Ca2+ pumps in plasma membrane of erythrocytes (prevent cell rigidity from accumulated calcium, erythrocytes remain flexible enough to move
Na/K Pump - an exchange pump that move one type of ion into cell against gradient while moving another type of ion out of cell against gradient, plasma membrane preserves steep gradient differences, continuously exports Na+ out of the cell and moves K into the cell
Vesicular Transport ( or Bulk Transport)
Involves energy input to transport large substances across the plasma membrane by a Vesicle (membrane-bound sac filled with materials
Organized into processes of :
Exocytosis - large substances secrete from cell, macromolecules too large to be moved across membrane, material packed within intracellular transport vehicles, vesicles and plasma membrane in fusion (requires ATP), contents released to outside of cell following fusion (ex: release of neurotransmitters from nerve cells)
Endocytosis - cellular uptake of large substances from external environment, steps in reverse of exocytosis (pocket invagination forms, pinches off to form vesicle), used for uptake of materials for digestion, retrieval of membrane protein composition to alter cellular processes
Types of Endocytosis (Phagocytosis, Pinocytosis, Receptor mediated Endocytosis)
Phagocytosis - cellular eating, occurs when a cell engulfs a large particle external to cells, forms pseudopodia, contents digested after fusing with lysosome, few cells perform this (ex: white blood cells engulfs and digests a microbe)
Pinocytosis - cellular drinking, multiple small vesicles formed, performed by most cells internalization of droplets of interstitial fluid containing dissolved solutes
Receptor-mediated Endocytosis - uses receptors on plasma membrane to bind molecules, enables cell to obtain bulk quantities of substances, ex: transport of cholesterol (bound to low-density lipoproteins (LDLs) from blood to cell
Membrane Transport Chart
Resting Membrane Potential (RMP)
Plasma membranes establishes and maintains electrochemical gradient, essential for muscle and nerve cell function
Electrical charge difference at membrane
Membrane potential - potential energy of charge difference
RMP - potential when cell is at rest
Two Conditions of RMP :
Unequal distribution of ions/molecules across plasma membrane (more K in cytoplasm than in fluid, more Na in in fluid than cytoplasm)
Unequal relative amounts of positive and negative charges (more positive outside)
Movement depends on electrochemical gradient, negatively charged proteins remain inside cells
Maintaining RMP - Na/K pumps significant
Na pump out and K pumped in, opposite directions, against concentration gradient
Ligand-Receptor Signaling and 3 Types of Receptors
Most cell communication occurs through ligands
3 Types of Receptors that bind ligands :
Channel linked receptos - permit ion passage into or out of cells, occures in response to neurotransmitter binding, help initiate electrical changes to RMP in muscle and nerve cells
Enzymatic Receptors - protein kinase enzymes, provides mechanism for altering enzymatic activity
G Protein Coupled Receptors - Indirectly activate protein kinase enzymes
Enzymatic Receptors - protein kinase enzymes, provides mechanism for altering enzymatic activity
G Protein Coupled Receptors - Indirectly activate protein kinase enzymes
