Transcript Cells Chapter 3    I. Overview Cell Membrane Cytoplasm   Cytosol Organelles Nonmembranous: Cytoskeleton, Microvilli, Centrioles, Cilia, Flagella, Ribosomes  Membranous: Mitochondria, Nucleus, Endoplasmic Reticulum, Golgi Apparatus, Lysosomes, Peroxisomes, Vesicles 

Cells
Chapter 3
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I. Overview
Cell Membrane
Cytoplasm
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Cytosol
Organelles
Nonmembranous: Cytoskeleton, Microvilli,
Centrioles, Cilia, Flagella, Ribosomes
 Membranous: Mitochondria, Nucleus, Endoplasmic
Reticulum, Golgi Apparatus, Lysosomes,
Peroxisomes, Vesicles
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II. Plasma Membrane (Cell Membrane)
"Fluid Mosaic Model" - plasma membrane is
composed of a double layer (bilayer) of
phospholipid molecules with proteins that
float/move among the phospholipids, yet the
plasma membrane is stable.
Proteins function....
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As cell markers for recognition by immune
system
As receptors (e.g for hormones)
As catalysts
Transportation
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Proteins in the membrane...
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integral proteins (maintain selective transport)
peripheral proteins (catalyst and mechanical
function)
The plasma membrane also contains a
myriad of biological compounds such as
glycoproteins, glycolipids, and
proteoglycans (all referred to as
glycocalyx) that extend outward from the
plasma membrane
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III. Cytoplasm
Cytoplasm is the material found inside the cell and is
divided into two subdivisions: cytosol
and organelles.
 Cytosol (intracellular fluid) contains dissolved
nutrients, ions, soluble and insoluble
proteins, and waste products.
 Organelles are structures that perform specific
functions within the cell and are classified as
membranous and non-membranous.
Mitochondria
Rod-like, double membrane, inner membrane folded into projections
called cristae; Site of ATP synthesis.
Ribosomes
Dense particles consisting of two subunits, each composed of ribosomal
RNA and proteins; can be free or it can be attached to ER; site of
protein synthesis
E. R. (rough)
Coiling membrane system with ribosomes attached; proteins
synthesized are packaged into vesicles for transport to the golgi
apparatus
E. R. (smooth)
Coiling membrane system lacking ribosomes; synthesizes lipids and
carbohydrates
Golgi
apparatus
Stack of smooth membrane sacs adjacent to the nucleus; modifies
synthesized proteins, then packages the proteins (e.g. lysosomes &
peroxisomes) in vesicles for transport around/out of cell
Lysosomes
Membranous sacs containing hydrolytic enzymes used in cell digestion
Peroxisomes
Membranous sacs containing oxidative enzymes (e.g. peroxidase) that
degrade toxic compounds such as hydrogen peroxide
Vesicles
Membrane bound sac that transports cellular material
Microfilaments
Filaments containing the contractile protein actin; part of the
cytoskeleton and functions in intracellular movement
Intermediate filaments
Protein fibers that provides strength, stabilize the position of
organelles, and transport materials within the cytoplasm
Microtubules
Hollow tubes composed of the globular protein tubulin;
microtubules provide strength and rigidity and anchoring major
organelles
Thick filaments
Large and long strands of myosin protein found in muscle cells that
interact with thin actin filaments to produce muscle contraction
Centrioles
Cylindrical structure composed of nine triplets of microtubules;
centrioles direct the movement of DNA during cell division as well
as form the bases of cilia and flagella
Microvilli
Small, finger-shaped projections of the cell membrane that actively
absorb fluid and nutrients
Cilia
Cell surface projections composed of microtubules; cilia move to
propel substance across the cell surface
Flagella
Larger and longer cilia that provides cellular locomotion (e.g.
human sperm)
Nucleus
Structure housing genetic information and is surrounded by a
membrane (nuclear envelope)
Endoplasmic Reticulum
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IV. Membrane Transport Processes
Transportation of materials across the cell membrane is
determined by the components in the membrane that
impart permeability.
Most cells have selective permeability, free passage
of some materials and restricts the passage of others.
Permeability may be based on size, electrical charge,
molecular shape, solubility, etc... Passage across the
membrane is classified as active (requiring energy) and
passive (not requiring energy)
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Membrane transport processes:
 Passive
 Diffusion - net movement of particles from an
area of higher concentration to an area of lower
concentration.
 Osmosis - diffusion of water through a selectively
permeable membrane
 Facilitated diffusion - diffusion of a substance
with the aid of a membrane carrier.
 Filtration - movement of water and solutes
through a semipermeable membrane from a region
of higher hydrostatic pressure to a region of lower
hydrostatic pressure
b) Osmosis – movement of a solvent (water)
through a semi- permeable membrane
down a concentration gradient (higher to
lower)
Solutions:
Isotonic
Hypertonic
Hypotonic
A human red blood cell is composed of 0.9%
salt and 99.1% water. If this cell is placed
in a solution of 0.9% salt and 99.1% water
(saline) the solution is isotonic and the
blood cell will remain unchanged
Isotonic
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The same RBC is placed in a beaker of
distilled water (100% H2O and 0% salt),
water will enter the cell and cause it to
burst (lysis). Water goes from higher conc.
to lower conc. This solution is hypotonic
(hypo=less salt in solution).
Hypotonic
The same RBC is placed in a beaker of 50%
salt water (50% H2O and 50% salt), water
will leave the cell and cause it to shrink
(crenation). Water goes from higher conc.
to lower conc. This solution is hypertonic
(hyper=more salt in solution).
Hypertonic
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Active
 Active transport - movement of a substance (with the aid
of a membrane carrier) through a membrane against its
concentration gradient.
 Exocytosis - substances enclosed in a vesicle fuses with the
plasma membrane, the vesicle then ruptures, releasing the
substances outside the cell.
 Endocytosis (types):
 Phagocytosis - the cell membrane extends outward
and encloses large particles which are then transported
into the cell.
 Pinocytosis - particles attach to the cell membranes
which collapses, causing particles to be taken into the
cell.
 Receptor-mediated - pinocytotic movement initiated
by protein receptors on the plasma membrane.
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Movement of particle may be....
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Symport - movement of two or more different
kinds of material in the same direction across
the cell membrane.
Uniport - movement of one type of material in
one direction across the cell membrane.
Antiport - moving two types of material across
the cell membrane in opposite directions.
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V. Cell Division (Cell Life Cycle)
Multicellular organisms develop from a zygote,
which is formed by the fusion of a sperm and an
egg (gametes). Each gamete has half the
compliment of chromosomes (haploid number)
and when combined gives rise to a zygote with a
complete set (diploid number) of chromosomes.
In order for the zygote to develop into a
multicellular organism, it must repeatedly
undergo cellular divisions. The series of events a
cell (or zygote) undergoes that ultimately
produces a new cell is called the cell cycle.
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Nucleus
- located in the center of the cell
- controls all functions of organelles
- cell reproduction/division takes place
- DNA (Deoxyribonucleic Acid) is housed
- blueprint of heredity
- as cell divides the DNA coil tightly, called
chromatin, to form chromosomes (46)
- bound by nuclear envelope: double layered
membrane enclosing nucleoplasm
Nucleoli: are darkly stained areas within the
nucleus that indicate rapid RNA synthesis.
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Cell Growth and reproduction: produces
two identical daughter cells from one
parent cell
- cell life cycle has two major sections
Interphase (cell growth; not
dividing)
G1 phase : growth
S phase: growth and DNA
synthesis
G2 phase: growth and final
preparation for cell division
Mitotic phase (M): dividing phase
Prophase
Metaphase
Anaphase
Telophase
IPMAT
Interphase: G1 , S and G2 phases. (90% of
its time)
G1 (gap 1): cell grows vigorously and
metabolically very active.
- depending on cell type, this
phase may last minutes to years.
- centrioles begin replicating
S: DNA replicates itself; chromatin
condenses. Ensures daughter cells
receive identical genetic information.
DNA replication (S phase)
G2: phase is very brief.
- centriole replication is complete
- ready to divide
Mitotic phase (M):
Prophase: Chromosomes are visible.
- early prophase: longest phase of mitosis.
- chromatin condenses to form chromosomes.
- centriole pairs start to separate/nuclear
membrane breaks down.
- mitotic spindles (microtubules) start to develop
late prophase:
- centrioles migrate away from each to
opposite poles of cell.
Metaphase: (meta = middle)
- chromosomes cluster toward the center of
cell.
- centromeres align along the equator of the
spindle
- enzyme separase will separate the
chromatid.
Anaphase: (“apart”) shortest phase.
- centromeres of the chromosomes split
- each chromatid becomes its own
chromosome
- Each chromosome is pulled to opposite pole
Telophase: begins when chromosomal
movement stops.
- chromosomes uncoil; goes back to fine
threads of chromatin.
- new nuclear envelope forms
- cytoplasm pinches inward forming a
cleavage furrow (cytokinesis)
Somatic (body) cells contain a diploid
number of chromosomes.
Human cells contain two sets of
chromosomes (one member from each
pair is inherited from each parent);
homologous chromosomes
2n (n= # of different chromosomes).
n=23 in humans
2(23)= 46
22 pairs are called autosomes while the last
pair determines the sex of the individual;
sex chromosomes (X and Y)
Mapping of chromosomes is called a
karyotype
What can cause abnormal cell division?
- radiation: UV light, x-ray
- viruses
- organic chemicals: pesticide, nicotine
Teratogens: substances that can cause
severe congenital abnormalities.
Carcinogens: chemical or environmental
agent that produces cancer
Cancer:
- The p53 gene prevents these mutations
from causing problems.
- p53 is present in all DNA
- p53 is responsible for cell division to stop so
that mutated DNA can be repaired.
- If DNA cannot be repaired the cell
undergoes apoptosis in which the cell is
programmed to die.
- Defective or missing p53 can result in the cell
mutating uncontrollably causing a tumor.
- Normal cells will divide on average about 50
times then the cell dies. While tumors divide
without stopping.
Benign tumors are cell masses that do not
fragment or spread beyond its original
area of growth.
Malignant tumors are cell masses that
break apart and spread or invade other
parts of the body. This movement is
metastasis.
Cancer is the term used to refer to any
tumor that has the potential to become
malignant.
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VI. Protein Synthesis
Ribonucleic acid (RNA) links DNA's genetic instructions
for making proteins to the process of protein synthesis
It copies or transcribes the message from DNA and then
translates that message into a protein.
RNA, like DNA, is a nucleic acid or polymer of
nucleotides
RNA structure differs from DNA in the following ways:
 The five carbon sugar in RNA nucleotides is ribose
rather than deoxyribose
 The nitrogenous base uracil is found in place of
thymine
PROTEIN SYNTHESIS
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The linear sequence of nucleotides in DNA ultimately
determines the linear sequence of amino acids in a
protein.
Nucleic acids are made of four types of nucleotides
which differ in their nitrogenous bases
Hundreds or thousands of nucleotides long, each gene
has a specific linear sequence of the four possible bases.
Proteins are made of twenty types of amino acids linked
in a particular linear sequence (the protein's primary
structure).
Information flows from gene to protein through two
major processes, transcription and translation.
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Transcription - the synthesis of RNA
using DNA as a template
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A gene's unique nucleotide sequence is
transcribed from DNA to a complimentary
nucleotide sequence in messenger RNA
(mRNA).
The resulting mRNA caries this transcript of
protein-building instructions to the cell's
protein-synthesizing machinery.
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Translation - synthesis of a
polypeptide, which occurs under the
direction of messenger RNA (mRNA)
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During this process, the linear sequence of
bases in mRNA is translated into the linear
sequence of amino acids in a polypeptide.
Translation occurs on ribosomes, complex
particles composed of ribosomal RNA (rRNA)
and protein that facilitate the orderly linking
of amino acids into polypeptide chains.
Signals are contained in the RNA to start and
stop translation.
SUMMARY OF PROTEIN SYNTHESIS
GENETIC CODE
Translation