Post on 10-Jul-2020
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Chapter 03
Lecture and
Animation Outline
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Functions
• Basic unit of life
• Synthesis of molecules
• Communication
• Cell metabolism and energy release
• Reproduction and inheritance (DNA)2
Cell Structure
• Organelles:
- specialized structures in cells that perform
specific functions
- Ex. Nucleus, mitochondria, ribosomes, etc.
• Cytoplasm:
jelly-like substance that holds organelles
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Microtubule
Peroxisome
Centrioles
Centrosome
Phagocytic
vesicle
Lysosome
fusing with
incoming
phagocytic
vesicle
Lysosome
Nucleus
Nuclear
envelope
Nucleolus
MicrovilliCilia
Secretory
vesicles
Golgi
apparatus
Smooth
endoplasmic
reticulum
Rough
endoplasmic
reticulum
Free
ribosome
Ribosome
Mitochondrion
Cell
membrane
Cytoplasm
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Cell Membrane
• What is it?
outermost component of a cell
• Functions:
- selective barrier
- encloses cytoplasm
• Extracellular: material outside cell
• Intracellular: material inside cell
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Structure of Cell Membrane
• Called Fluid Mosaic Model
• Made of phospholipids and proteins
• Phospholipids form a double layer or bilayer
• Phospholipids contain 2 regions: polar and
nonpolar
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• Polar regions:
- “heads”
- hydrophilic (H2O loving)
- exposed to H2O
• Nonpolar regions:
- “tails”
- hydrophobic (H2O fearing)
- away from H2O
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Figure 2.14b
Figure 3.2a
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Movement through Cell Membrane
• Cell membrane selectively determines what can
pass in and out of the cell.
• Enzymes, glycogen, and potassium are found in
higher concentrations INSIDE the cell.
• Sodium, calcium, and chloride are found in higher
concentrations OUTSIDE the cell.
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Ways molecules Pass through Cell Membrane
1. Directly through (diffusion):
O2 and CO2 (small molecules)
2. Membrane channels:
- proteins that extend from one side of cell
membrane to other
- size, shape, and charge (+/-) determine what can
go through
- Ex. Na+ passes through Na+ channels
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3. Carrier molecules:
- bind to molecules, transport them across, and
drop them off
- Ex. glucose
4. Vesicles:
- can transport a variety of materials
- fuse with cell membrane
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Gated Na+
channel
(open)
Gated Na+
channel (closed)
K+ leak
channel
(always open)K+
Na+
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Diffusion• What is it?
movement of molecules from areas of high to low concentration
• Solution:
solid, liquid, or gas that contains one or more solutes
• Solute:
substance added to solvent that dissolves
• Solvent:
substance such as H2O that solute is being added to
Ex. Add salt to H2O. H2O =solvent, salt=solute,
mixture=solution
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• Concentration gradient:
- measures conc. difference at 2 points
- greater the distance the faster the solute
will travel
• Filtration:
movement of fluid through a partition with holes
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Mediated Transport Mechanisms
• Facilitated diffusion:
- diffusion with aid of a carrier molecule
- requires no ATP
• Active transport:
- moves substances from low to high conc.
- requires ATP
- Ex. Sodium-potassium pump
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Na+–K+ pump
Three sodium ions (Na+) and adenosine
triphosphate (ATP) bind to the
sodium–potassium (Na+–K+) pump.
Na+–K+ pump
changes shape
(requires energy).The ATP breaks down to adenosine diphosphate
(ADP) and a phosphate (P) and releases energy.
That energy is used to power the shape change in the
Na+–K+ pump.
The Na+–K+ pump changes shape, and the Na+ are
transported across the membrane and into the
extracellular fluid.
Two potassium ions (K+) bind to the Na+–K+ pump.
The phosphate is released from the Na+–K+ pump
binding site.P
K+
Na+–K+ pump
resumes original
shape.
The Na+–K+ pump changes shape, transporting K+
across the membrane and into the cytoplasm. The
Na+–K+ pump can again bind to Na+ and ATP.
P
ATP
Na+
Na+
K+
ADP
K+Na+
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K+
A Na+–K+ pump maintains a concentration of Na+ that is higher outside
the cell than inside.
Na+ move back into the cell by a carrier molecule that also moves glucose.
The concentration gradient for Na+ provides the energy required to move
glucose, by cotransport, against its concentration gradient.
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1
2
Na+–K+
pump Na+
Carrier
molecule
Glucose
Glucose
Na+
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Osmosis
• What is it?
diffusion of water across a cell membrane
• Osmotic pressure:
force required to prevent movement of water across
cell membrane
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*
1 2 3
Because the tube contains salt ions
(green and pink spheres) as well
as water molecules (blue spheres),
there is proportionately less
water in the tube than in the beaker,
which contains only water. The
water molecules diffuse with their
concentration gradient into the
tube (blue arrows). Because the
salt ions cannot leave the
tube, the total fluid volume inside
the tube increases, and fluid moves
up the glass tube (black arrow) as a
result of osmosis.
The solution
stops rising when
the weight of the
water column
prevents further
movement of
water into the
tube by osmosis.
Water moves by osmosis into
the tube until the weight of
the column of water in the
tube (hydrostatic pressure)
prevents further movement
of water into the tube. The
hydrostatic pressure that
prevents net movement of
water into the tube is equal
to the osmotic pressure of
the solution in the tube.
The tube is immersed in
distilled water. Water
moves into the tube by
osmosis (see inset above*).
The concentration of salt in
the tube decreases as
water rises in the tube
(lighter green color ).
Distilled
water
Water
Selectively
permeable
membrane
3% salt solution
Weight
of water
columnSalt solution
rising
Osmosis
The end of a tube
containing a 3% salt
solution (green) is closed
at one end with a
selectively permeable
membrane, which allows
water molecules to pass
through but retains the
salt ions within the tube.
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Types of Osmotic Solutions
• Hypotonic solution:
- lower conc. of solutes outside cell
- higher conc. of H2O outside cell
- H2O moves into cell
- lysis (burst)
• Hypertonic solution:
- higher conc. of solutes outside cell
- higher conc. H2O inside cell
- H2O moves out
- crenation (shrinks)
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• Isotonic solution:
- equal conc. of solutes
- water doesn’t move
- cell remains intact
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Endocytosis• What is it?
process that brings materials into cell using
vesicles
• 2 types
- Phagocytosis:
cell eating (solid particles)
- Pinocytosis:
cell drinking (liquid particles)
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Exocytosis
• What is it?
process that carries materials out of cell
using vesicles
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The vesicle membrane
fuses and the vesicle
separates from the cell
membrane.
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2
3
Receptor
molecules
Molecules to
be transported
Receptor molecules on
the cell surface bind to
molecules to be taken
into the cell.
The receptors and the
bound molecules are
taken in to the cell as a
vesicle is formed.
Cell membrane
Vesicle
2
1
3
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Cell Structures
• Cytoplasm
Location: inside cell
Characteristic: jelly-like fluid
Function: give cell shape and hold organelles in
place
• Nucleus
Location: center of cell
Characteristic: all cells contain nucleus at some
point
Function: houses DNA
• Nuclear envelope:
Location: edge of nucleus
• Nuclear pores:
Location: surface of nucleus
Function: where materials pass in and out of
nucleus
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Figure 3.13a
• Chromosome:
Location: inside nucleus
Characteristic: made of DNA and proteins
Function: part of genetic makeup
• Chromatin:
Location: inside nucleus
Characteristic: loosely coiled chromosomes
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• Nucleolus
Location: in nucleus
Function: produce ribosomes
• Ribosome
Location: attached to RER or cytoplasm
Function: produce proteins
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Ribosomal proteins, produced in the
cytoplasm, are transported through
nuclear pores into the nucleolus.
The small and large ribosomal subunits
leave the nucleolus and the nucleus
through nuclear pores.
rRNA, most of which is produced in the
nucleolus, is assembled with ribosomal
proteins to form small and large ribosomal
subunits.
The small and large subunits, now in the
cytoplasm, combine with each other and
with mRNA during protein synthesis.
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3
4
1
2
3
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rRNA
Ribosomal
proteins from
cytoplasm
Small
ribosomal
unit
Large
ribosomal
unit
Nuclear pore
mRNA
Ribosome
Nucleolus
Nucleus
DNA
(chromatin)
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• RER (Rough Endoplasmic Reticulum)
Location: cytoplasm
Characteristic: membranes with ribosomes attached
Function: site of protein synthesis
• SER (Smooth Endoplasmic Reticulum)
Location: cytoplasm
Characteristic: membranes with no ribosomes
Function: site of lipid synthesis (Ex. Cholesterol)
Figure
3.16
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• Golgi apparatus
Location: cytoplasm
Characteristic: closely, packed stacks of
membranes
Function: collect, sort, package, and distribute
proteins and lipids
• Secretory vesicle
Location: cytoplasm
Function: distributes materials out of cell
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• Lysosome
Location: cytoplasm
Function: enzymes that digest foreign material
• Mitochondria
Location: cytoplasm
Characteristic: contains folds (cristae)
Function: produces ATP
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• Cilia
Location: cell surface
Characteristic: many per cell
Function: move materials across cell’s surface
• Flagella
Location: cell surface
Characteristic: 1 per cell
Function: move cell, Ex. sperm
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• Microvilli
Location: cell surface
Characteristic: shorter than cilia
Function: increase surface area
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Cytoskeleton
• What is it?
- cell’s framework
- made of proteins
• Functions:
- provide support
- hold organelles in place
- enable cell to change shape
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Types of Cytoskeleton
• Microtubules:
- largest diameter
- provide structural support
- form cilia and flagella
• Intermediate filaments:
- medium diameter
- maintain cell shape
• Microfilaments:
- smallest diameter
- involved in cell movement
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TEM 60,000x
Centriole
(in longitudinal
section)
Centriole
(in cross
section)
(b)
Microtubule
triplet
(a)
(b): © Biology Media/Photo Researchers, Inc.
Whole Cell Activity• A cell’s characteristics are determine by the
type of proteins produced
• Proteins’ function is determined by genetics
• Information in DNA provides the cell with a
code for its cellular processes
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DNA
• What is it?
- double helix in nucleus
- composed of nucleotides
- contains 5 carbon sugar (deoxyribose,
nitrogen base, phosphate
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Flow of Genetic Information
• Also called Central Dogma
• Occurs in three stages:
– DNA replication
– Transcription
– Translation
DNA
Replication
Gene Expression
• What is it?
- information in DNA directs protein
synthesis
- proteins provide code for gene expression
- enzymes regulate chemical reactions
- uses transcription and translation
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Transcription
• What is it?
- process by which DNA is “read”
- occurs in ribosomes
- produces mRNA (messenger RNA)
- mRNA contains codons
- codons: set of 3 nucleotide bases that code for
a particular amino acid
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Translation
• What is it?
- process by mRNA is converted into amino
acids (polypeptides)
- produces proteins
- codons pair with anticodons
- anticodons: 3 nucleotide bases carried by tRNA
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Cell Division
• What is it?
- formation of 2 daughter cells from a single
parent cell
- uses mitosis and meiosis
- each cell (except sperm and egg) contains
46 chromosomes (diploid)
- sperm and egg contain 23 chromosomes
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Mitosis
• What is it?
- cell division that occurs in all cells except
sex cells
- forms 2 daughter cells
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Components of Mitosis
• Chromatid:
2 strands of chromosomes that are genetically
identical
• Centromere:
where 2 chromatids are connected
• Centrioles:
small organelle composed of 9 triplets
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Stages in Mitosis
1. Interphase:
- time between cell divisions
- DNA is in strands (chromatin)
- DNA replication occurs
2. Prophase:
- chromatin condenses into chromosomes
- centrioles move to opposite ends
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3. Metaphase:
chromosomes align
4. Anaphase:
- chromatids separate to form 2 sets of
chromosomes
- chromosomes move towards centrioles
5. Telophase:
- chromosomes disperse
- nuclear envelopes and nucleoli form
- cytoplasm divides to form 2 cells74
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