Download Chapter 3: The Living Units

Chapter 3: The Living Units
Objectives:
1. Define cell.
2. List the three major regions of a generalized cell and indicate the
function of each.
3. Describe the chemical composition of the plasma membrane and
relate it to membrane functions.
4. Compare the structure and function of tight junctions,
desmosomes, and gap junctions.
5. Relate plasma membrane structure to active and passive transport
mechanisms. Differentiate between these transport processes
relative to energy source, substances transported, direction and
mechanism.
6. Define membrane potential and explain how the resting membrane
potential is maintained.
7. Describe the role of the glycocalyx when cells interact with their
environment.
8. List several roles of membrane receptors and that of voltagesensitive membrane channel proteins.
9. Describe the composition of the cytosol; define inclusions and list
several types.
10. Discuss the structure and function of mitochondria.
11. Discuss the structure and function of ribosomes, the endoplasmic
reticulum, and the Golgi apparatus including function
interrelationships among these organelles.
12. Compare the functions of lysosomes and peroxisomes.
13. Name and describe the structure and function of cytoskeletal
elements.
14. Describe the roles of centrioles in mitosis and in formation of cilia
and flagella.
15. Outline the structure and function of the nuclear envelope,
nucleolus, and chromatin.
16. List the phases of the cell life cycle and describe the key events
of each phase.
17. Describe the process of DNA replication.
18. Define gene and genetic code and explain the function of genes.
19. Name the two phases of protein synthesis and describe the roles
of DNA, mRNA, tRNA, and rRNA in each phase. Contrast triplets,
codons, and anticodons.
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20. Describe the importance of ubiquitin degradation of soluble
proteins.
21. Name and describe the composition of extracellular materials.
22. Discuss some theories of cell differentiation and aging.
Cell: structural units of all living things
I. Overview of the Cellular Basis of Life
A. Robert Hooke
1. observed plant cells in 1600s
B. Schleiden and Schwann
1. said living things were composed of cells in 1830s
C. Virchow
1. said cells only come from other cells
D. Cell Theory
1. A cell is the basic structural and functional unit of living
organisms. So when you define cell properties you are in fact
defining the properties of life.
2. The activity of an organism depends on both the individual and
the collective activities of its cells.
3. According to the principle of complementarity, the biochemical
activities of cells are dictated by the relative number of their
specific subcellular structures.
4. Continuity of life has a cellular basis.
E. Cell
1. varies in size, shape, function
2. Generalized, Composite Cell
a. plasma/cell membrane
b. cytoplasm
c. nucleus
II. The Plasma Membrane: Structure
A. Plasma Membrane
1. separates the body’s 2 major fluid compartments
a. intracellular fluid
b. extracellular fluid
B. The Fluid Mosaic Model
1. Fluid Mosaic Model
a. idea of plasma membrane as a think structure composed of a
bilayer of lipid (phospholipids) molecules
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b. protein molecules dispursed in bilayer constantly change
c. hydrophilic
1. head of phospholipids
2. hydro = water
3. philic = loving
d. hydrophobic
1. tail of phospholipids
2. phobic = hating
e. integral proteins
1. proteins firmly inserted into the lipid bilayer
2. transmembrane – go through the entire membrane layer
3. transporting things into & out of cell
4. channels – pores formed in membrane
5. carriers – bind to a substance and then movie it through
membrane
6. signal transduction – receptors that relay messages
f. periphe ral proteins
1. attached loosely to integral proteins or membrane lipid
2. supporting filaments
3. enzymes
4. mechanical functions
III. Specializations of the Plasma Membrane
A. Microvilli
1. minute fingerlike extensions of the plasma membrane project
from free or exposed cell surface
2. increase surface area
3. often found on absorptive cells; intestinal cells
B. Membrane Junctions
1. Tight Junctions
a. series of integral protein fused together to form impermeable
junction
b. prevents molecules from passing through extracellular space
c. found in epithelial cells lining the digestive tract
2. Desmosomes
a. anchoring junctions
b. spot welds between cells
c. found in tissues subjected to great mechanical stress; skin,
heart muscle
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3. Gap Junctions
a. communicating junction between adjacent cells
b. found in heart and smooth muscle
IV. The Plasma Membrane: Functions
A. Membrane Transport
1. Intersti tial Fluid
a. extra cellular fluid our cells are bathed in
b. helps to “feed” our cells
2. Selectively (differentially) Permeable Membrane
a. allows some things to pass, but blocks others
b. allows nutrients to enter cell
c. allows cell proteins to stay in cell, lets waste out
3. Two ways things enter/exit cell
a. Passive Processes
1. substances cross membrane without energy from cell
a. Diffusion
1) tendency of molecules or ions to scatter evenly
throughout the environment
2) molecules move from an area of higher
concentration to an area of lower concentration
3) molecules move along or down a concentration
gradient
b. Simple Diffusion
1) unassisted diffusion of lipid-soluble or very small
particles
2) Osmosis
a) unassisted diffusion of a solvent (water)
through membrane
3) oxygen, carbon dioxide, fat-soluble vitamins
c. Facilitated Diffusion
1) type of diffusion of molecules that cannot pass
through the membrane because they are
dissolved in water
2) get help from carrier proteins or channels
3) carrie r – transmembrane integral protein
4) channel – transmembrane tunnels
d. Osmosis
1) diffusion of a solvent through a selectively
permeable membrane
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2) occurs when water concentration differs on both
sides of cells
3) osmolarity – the total concentration of all solute
particles in a solution
4) if the membrane is impermeable to solute molecules
the volume of the solution will change
5) hydrostati c pressure – back pressure exerted by
water against membrane
6) water will diffuse until hydrostatic pressure is equal
to osmotic pressure
7) osmotic pressure – cell’s tendency to resist net
water entry
8) toni city – ability of a solution to change shape or
tone of cell by altering internal water volume
a) isontonic – solution with the same
concentration of solute inside and outside of cell
1. 0.9% saline
2. 5% sucrose
3. no net loss or gain of water
b) hypertoni c – solution with higher solute
concentration outside cell
1. cells lose water
2. cell shrink
c) hypotonic – solution with lower solute
concentration outside cell
1. cells gain water
2. cell burst (lyse)
e. Flitration
1) process that forces water and solutes through a
membrane or capillary wall by fluid or hydrostatic
pressure
2) used pressure gradient – pushes solutecontaining fluid from a higher-pressure area to a
lower pressure area
3) not selective
b. Active Processes
1. substances cross membrane with energy from cell
2. usually used with substances too large to pass through on
their own
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a. active transport – requires carrier proteins to go
against concentration gradient
b. vesicular transport – large particles and fluids are
transported across plasma and intracellular membranes
1) exocytosis – moving things out of the cell
2) endocy tosis – moving things into the cell
3) transcytosis – moving substances into, across, and
out of cell
4) trafficking – moving substances from one part of
the cell to another
5) phagocytosis – cell eating
6) pinocy tosis – cell drinking
V. The Cytoplasm
A. cell-forming material
B. cellular material between the plasma membrane and nucleus
C. 3 parts
1. cytosol – viscous, semi-transparent fluid, in which the other
elements are suspended
2. cytoplasmic organelles – metabolic machinery of the cell
3. inclusions – chemical substances that may or may not be
present
D. Cytoplasmic Organelles
1. 2 types
a. nonmembranous organelles – lack membranes
1) cytoskeleton
2) centrioles
3) ribosome
b. membranous organelles – have membrane to maintain internal
environment different than surrounding cytosol
1) mitochondria
2) peroxisome
3) lysosome
4) endoplasmic reticulum
5) Golgi apparatus
c. helps to keep biochemical activity organized
2. Mitochondria
a. threadlike or sausage-shaped membranous organelles
b. change shape constantly
c. power house of cell – ATP supply
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3.
4.
5.
6.
d. density in cell reflects energy requirement
e. enclosed in 2 membranes
1) outside membrane not special
2) inside membrane folded in on itself forming cristae
f. gel-like substance within Mitochondria called matrix
g. site of cellular respiration
Ribosomes
a. small granules composed of protein and DNA
b. site of protein synthesis
c. some free floating, some attached to membranes (RER)
d. make 2 types of proteins
Endoplasmic Reticulum (ER)
a. extensive system of interconnected tubes and membranes
enclosing fluid filled cavities (cisternae)
b. continuous with nuclear membrane
c. 2 varieties
1) Rough Endoplasmic Reticulum (RER)
a) external surface studded with ribosomes
b) functions
1. manufacture proteins
2. form part of all cellular membranes
3. enzyme active sites on external face of ER
membrane
2) Smooth Endoplasmic Reticulum (Smooth ER)
a) enzymes catalyse reactions
1. lipid metabolism, cholesterol synthesis
2. synthesis of sex hormones
3. absorption, synthesis and transport of fats
4. detox of drugs, pesticides and carcinogens
5. breakdown of stored glycogen to form free glucose
Golgi Apparatus (Body)
a. stacked and flattened membranous sacs
b. modify, concentrate & package proteins & lipids made at RER
c. secretory vesicles – contain proteins destined for export
Lysosomes
a. spherical membranous organelles containing digestive
enzymes
b. large & abundant in phagocytes
c. functions to
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1) digest particles taken in by endocytosis (bacteria, viruses,
toxins
2) degrading warn-out or nonfunctional organelles
3) perform metabolic functions (glycogen
breakdown/release)
4) break down nonuseful tissues
5) break down bone to release calcium ions
7. Endomembrane system
a. system of organelles work together to
1) produce, store, export biological molecules
2) degrade potentially harmful substances
b. organelles
1) ER
2) Golgi apparatus
3) secretory vesicles
4) lysosomes
5) nuclear membrane
8. Peroxisomes
a. membranous sacs containing a variety of powerful enzymes
b. neutralize free radicals – highly reactive chemicals
9. Cytoskeleton
a. cell skeleton
b. 3 types of rods
1) microtubules
a) element with largest diameter, hollow tubes
b) radiate from a small region called centrosome
c) determine overall shape of cell, distribution of
organelles
2) microfilaments
a) strengthens cell surface
b) responsible for membrane changes of endocytosis and
exocytosis
3) intermediate filaments
a) tough insoluble protein fibers
b) act as internal guy-wires to resist pulling motion on cell
4) centrosome
a) microtubules anchored near nucleus
b) containes paired centrioles – small barrel-shaped
organelles oriented at right angles forms mitotic
spindle
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E. Cellular Extensions
1. Cilia
a. whiplike motile cellular extensions, occur in large numbers, on
exposed surfaces of certain types of cells
b. moves substances in one direction across cell surface
2. Flagella
a. long singular cilia
b. propels cell itself
VI. The Nucleus
A. Control center of cell
B. Genetic Library
1. contains all instructions to build body’s proteins
2. dictates kinds and amounts of proteins to be synthesized
C. Most cells have one nucleus, some are multinucleate
1. skeletal muscle
2. bone desruction
3. liver cells
D. Once cell is anucleate
1. mature red blood cell
E. 3 structures
1. nuclear envelope
2. nucleoli
3. chromatin
F. Nuclear Envelope (Membrane)
1. Double membrane barrier separated by fluid filled space
2. Outer membrane continuous with RER
3. Nuclear Pore – areas where 2 membranes fuse
4. Selectively permeable
5. Contains nucleoplasm – like cytoplasm/cytosol
G. Nucleoli
1. Sites where ribosome subunits are assembled
2. Usually 1 or 2 per nucleus
H. Chromatin
1. 30% DNA
2. 60% Histone Protei n
a. compact the DNA
b. gene regulation
3. 10% RNA
4. Form chromosomes when cell is preparing to divide
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VII. Cell Growth and Reproduction
A. The Cell Life Cycle
1. Series of changes a cell goes through from the time it is formed
until it reproduces
2. 2 Major Periods
a. Interphase
1) cell growth
2) cell carries on normal activities
b. Cell Division
1) Mitotic Phase
3. Interphase
a. period from cell formation to cell division
b. metabolic phase
c. growth phase
4. Subphases
a. G 1 (gap 1)
1) cell is metabolically active
2) synthesizing proteins
3) rapid growth
b. G 0
1) phase for cells that permanently cease dividing
c. S phase
1) DNA replicates
2) new Histone proteins formed
d. G2
1) final phase of interphase
2) enzymes, proteins (other organelles) are replicated
5. DNA Replication
a. DNA helix begins to unwind
b. Enzyme untwists double helix and separates DNA
c. Free nucleotides serve as a template for a new DNA strand
d. New DNA segments spliced together
6. Mitosis
a. 4 phases
1) Prophase
a) distinct pairs of chromosomes become apparent
(tightly coiled DNA and protein)
b) each pair of chromosomes is made of identical sister
chromatids, held together by a centromer
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c) pairs of centrioles migrate to opposite ends of the cell,
form spindle fibers between them
d) nuclear envelope and nucleolus disappear
2) Metaphase
a) chromosomes line up midway between centrioles
b) centromere holding each pair of chromosomes together
attaches to spindle fiber between centrioles
3) Anaphase
a) centromere holding chromosome pair together
separates
b) individual chromosomes migrate in opposite directions
on the spindle fibers toward polar centrioles
c) cytokinesis begins
4) Telophase
a) chromosomes complete migration toward centrioles
b) nuclear envelopes develop around each set of
chromosomes
c) nucleoli develop
d) spindle fibers disappear
e) cleavage furrow nearly complete
7. Cytokinesis
a. division of the cytoplasm
B. Protein Synthesis
1. Gene
a. segment of DNA that carries instructions for creating one
protein
b. nucleotide bases are “letters” of DNA
c. triplet – sequence of 3 bases that form “words” or amino
acids
d. tRNA – transfer RNA
e. rRNA – ribosomal RNA
f. mRNA – messenger RNA
2. Transcri ption
a. the transfer of information from a DNA gene’s base sequence
to the complementary base sequence of an mRNA molecule
b. codon – 3-base sequence of mRNA
3. Translation
a. language of nucleic acids is translated into the language of
proteins
b. anticodon – 3-base sequence of tRNA
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