Exam 2 : Lecture

Question 1

Microscopy

Answer 1

Using microscope to view small-scale structures, staining techniques provide contrast

Question 2

How Are Cells Studied?

Answer 2

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

Question 3

Cells Size and Shape

Answer 3

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

Question 4

The Range of Cell Sizes

Answer 4

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

Question 5

The Variety of Cell Shapes

Answer 5

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

Question 6

Three Main Structural Features of A Cell

Answer 6

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)

Question 7

Cytoplasmic Components (Cytosol, Organelles - membrane bound and non membrane bound, Inclusions)

Answer 7

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

Question 8

Structure of A Cell

Answer 8

Question 9

General Functions Cells Perform

Answer 9

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

Question 10

What is the advantage of using a TEM instead of an LM to study intracellular structure?

Answer 10

TEM provides greater magnification and resolution than LM allowing for more details to e seen

Question 11

Which cell is larger, an erythrocyte or a human oocyte? What are their respective sizes?

Answer 11

Human oocyte : 120um , while red blood cell (erythrocyte) is 7-8 um

Question 12

Diagram the three main components of the cell and label the plasma membrane, nucleus, and cytoplasm.

Answer 12

Question 13

What cellular structure is responsible for forming the boundary of a cell and maintaining its integrity?

Answer 13

Plasma Membrane

Question 14

Lipid Components of Plasma Membrane

Answer 14

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

Question 15

Lipid Components (Phospholipids, Cholesterol, Glycolipids)

Answer 15

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

Question 16

Structure and Function of the Plasma Membrane

Answer 16

Question 17

Membrane Proteins

Answer 17

Half of plasma membrane by weight, float and move in fluid bilayer, performs most of membranes functions

Two Structural Types :

Integral Proteins - embedded within and extended across, phospholipid bilayer hydrophobic regions interact w/ hydrophobic interior, hydrophilic regions are exposed to aqueous environments on either side of membrane, many are glycoproteins (protein+carbohydrate)

Peripheral Proteins - not embedded in lipid bilayer, loosely attached to external or interior surfaces of membrane

Question 18

Functional Categories of Proteins (6 Major Roles Played by Membrane Proteins)

Answer 18

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

Question 19

How do lipids maintain the basic physical barrier of the plasma membrane?

Answer 19

The function as hydrophobic barriers

Question 20

What type of plasma membrane protein provides the means for moving materials across the plasma membrane? What are three subtypes?

Answer 20

Transport proteins : carriers, channels, pumps

Question 21

Membrane Transport (2 Categories)

Answer 21

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)

Question 22

Passive Processes : Diffusion (Simple and Facilitated Diffusion)

Answer 22

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

Question 23

Simple Diffusion

Answer 23

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

Question 24

Facilitated Diffusion

Answer 24

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

Question 25

Passsive Processes : Osmosis

Answer 25

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.

Question 26

Osmotic Pressure

Answer 26

Pressure exerted by movement of water across semipermeable membrane Hydrostatic Pressure - pressure exerted by a fluid on the inside wall of its container

Question 27

Osmosis and Tonicity

Answer 27

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

Question 28

Active Processes (Active Transport)

Answer 28

Organized into active transport and vesicular transport Active Transport - movement of solute against its concentration gradient, maintains gradient between cell and interstitial fluid, source of energy determines whether movement is primary or secondary Primary - uses directly from breakdown of ATP Phosphorylation of carrier occurs - breakdown of ATP results in phosphate group added to transport protein, changes proteins shape and result in movement of substance across the membrane Secondary - uses energy from movement of second substance down its gradient kinetic energy providing power to pump other substance, dependent on Na/K pumps for energy, Na moves down concentration gradient Two Types : Symport - two substances moved in same direction (symporters) process is called symport secondary active transport Antiport - two substances move in opposite directions (antiporters), called antiport secondary active transport

Question 29

Active Processes (Ion Pumps, Sodium-Potassium Pump

Answer 29

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

Question 30

Vesicular Transport ( or Bulk Transport)

Answer 30

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

Question 31

Types of Endocytosis (Phagocytosis, Pinocytosis, Receptor mediated Endocytosis)

Answer 31

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)

Question 32

Pinocytosis - cellular drinking, multiple small vesicles formed, performed by most cells internalization of droplets of interstitial fluid containing dissolved solutes

Answer 32

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

Question 33

Clinical View : Familial Hypercholesterremia

Answer 33

Inherited genetic disorder, defects in LDL receptor or proteins of LDLs, results in elevated cholesterol causes atherosclerosis, increased risk of heart attack

Question 34

Membrane Transport Chart

Answer 34

Question 35

Resting Membrane Potential (RMP)

Answer 35

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

Question 36

Ligand-Receptor Signaling and 3 Types of Receptors

Answer 36

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

Question 37

Enzymatic Receptors - protein kinase enzymes, provides mechanism for altering enzymatic activity

Answer 37

G Protein Coupled Receptors - Indirectly activate protein kinase enzymes