Transcript PowerPoint

Chapter 3:
The Cellular
Level of Organization
1
Cellular Organization
• Cell = smallest living unit
• Performs all life functions
2
Figure 3–1
Two Categories of Cells
• Sex cells (germ cells):
– reproductive cells
– male sperm
– female oocytes (eggs)
• Somatic cells (soma = body):
– all body cells except sex cells
3
Cellular Organization
• Different cells have different shapes
• Unique morphology is related to function
• All cells surrounded by plasma membrane:
– Separates cells from the environment
• Plasma membrane “holds in” the cytoplasm
• Cytoplasm consists of cytosol (fluid) and
organelles (structures)
• Body cells surrounded by interstitial fluid
– Interstitial fluid = fluid outside the membrane
4
Organelle Functions
Table 3–1 (1 of 2)
5
Organelle Functions
Table 3–1 (2 of 2)
6
The structures
and functions of the
cell membrane.
7
1. The Plasma (Cell) Membrane
- Mostly phospholipid bilayer
- Interface between cell and environment
8
Figure 3–2
Functions of Plasma (Cell) Membrane
• Physical barrier:
– Maintain homeostasis:
• Separates intracellular fluid from extracellular fluid,
different conditions in each
• Regulates exchange with environment:
– ions and nutrients enter
– waste and cellular products released
• Monitors the environment:
– extracellular fluid composition
– Cell communication and signaling
• Structural support:
– anchors cells and tissues
9
Plasma Membrane: Components
•
•
•
•
Phospholipid bilayer
Cholesterol: resist osmotic lysis
Carbohydrates
Proteins
10
Plasma Membrane: Components
1. Phospholipid Bilayer:
– hydrophilic heads—toward watery
environment, both sides
– hydrophobic fatty-acid tails—inside
membrane
– barrier to ions and water soluble
compounds
2. Cholesterol: resist osmotic lysis
11
Plasma Membrane: Components
3. Carbohydrates:
• Membrane Carbohydrates including:
– Proteoglycans, glycoproteins, and glycolipids
• extend outside cell membrane
• form sticky carb layer or “sugar coat”
called the glycocalyx
12
Functions of Membrane
Carbohydrates
• Lubrication and protection
• Anchoring and locomotion
• Specificity in binding
– Acts as receptors
• Recognition
– Self recognition
– immune response
13
Plasma Membrane: Components
4. Protein:
– ½ mass of membrane
– Integral proteins: span width of membrane
• within the membrane
– Peripheral proteins:
• Adhere to inner or outer surface of the
membrane
14
6 Functions of Membrane Proteins
1. Anchoring proteins (stabilizers):
–
attach to inside or outside structures
2. Recognition proteins (identifiers):
–
Self identification by immune system
–
Label cells normal or abnormal
3. Enzymes:
–
catalyze reactions in cytosol in extra cellular fluid
4. Receptor proteins:
–
bind and respond to ligands (ions, hormones) or
signaling, or import/export
5. Carrier proteins:
–
transport specific solutes through membrane
6. Channels:
–
15
regulate water flow and solutes through membrane
Which component of the cell membrane is
primarily responsible for the membrane’s ability
to form a physical barrier between the cell’s
internal and external environments?
A.
B.
C.
D.
phospholipid bilayer
glycocalyx
peripheral proteins
proteoglycans
16
Which type of integral protein allows
water and small ions to pass through
the cell membrane?
A.
B.
C.
D.
receptor proteins
carrier proteins
channel proteins
recognition proteins
17
How things get in
and out of cells.
18
Overcoming the Cell Barrier
• The cell membrane is a barrier, but:
– nutrients must get in
– products and wastes must get out
• Permeability determines what moves in
and out of a cell:
• A membrane that:
– lets nothing in or out is impermeable
– lets anything pass is freely permeable
– restricts movement is selectively permeable
19
Selective Permeability
• Cell membrane is selectively permeable:
– allows some materials to move freely
– restricts other materials
• Restricts materials based on:
–
–
–
–
size
electrical charge
molecular shape
lipid solubility
20
Transport
• Transport through a cell membrane can
be:
– active (requiring energy and ATP)
– passive (no energy required)
• 3 Categories of Transport
– Diffusion (passive)
– Carrier-mediated transport (passive or
active)
– Vesicular transport (active)
21
Solutions
• All molecules are constantly in motion
• Molecules in solution move randomly
• Random motion causes mixing
22
Concentration Gradient
• Concentration is the amount of solute
(glucose) in a solvent (e.g. H20)
• Concentration gradient:
– more solute in 1 part of a solvent than another
• Function = Diffusion
–
–
–
–
molecules mix randomly
solute spreads through solvent
eliminates concentration gradient
Solutes move down a concentration gradient
• From high concentration to low concentration
23
Factors Affecting Diffusion Rates
• Distance the particle has to move
• Molecule size:
– smaller is faster
• Temperature:
– more heat, faster motion
• Gradient size:
– the difference between high and low concentration
• Electrical forces:
– opposites attract, like charges repel
24
Diffusion and the Cell Membrane
• Diffusion can be simple or channel-mediated
25
Figure 3–15
Simple Diffusion
• Materials which diffuse through cell
membrane:
– lipid-soluble compounds (alcohols, fatty
acids, and steroids)
– dissolved gases (oxygen and carbon
dioxide)
26
Channel-Mediated Diffusion
• Materials which pass through transmembrane
proteins (channels):
– are water soluble compounds
– are ions
• Passage depends on:
– size
– charge
– interaction with
the channel
27
Osmosis
• Osmosis is the diffusion of water across
the cell membrane
28
Figure 3–16
How Osmosis Works
• More solute molecules, lower concentration
of water molecules
• Membrane must be freely permeable to
water, selectively permeable to solutes
• Osmosis Water Movement
– Water molecules diffuse across membrane
toward solution with more solutes
– Volume increases on the side with more solutes
• Osmotic Pressure
– Is the force of a concentration gradient of water
– Equals the force (hydrostatic pressure) needed to
29
block osmosis
Osmotic Pressure
30
Isotonic
• A solution that does not
cause osmotic flow of
water in or out of a cell
– iso = same, tonos = tension
• The osmotic effect of a
solute on a cell:
– 2 fluids may have equal
osmolarity
31
Figure 3–17a
Cells and Hypotonic Solutions
• hypo = below
• Has less solutes
– Loses water through osmosis
• A cell in a hypotonic
solution:
– gains water
– ruptures (hemolysis of red
blood cells)
Lysis
32
Figure 3–17b
Cells and Hypertonic Solutions
• hyper = above
• Has more solutes
– Gains water by osmosis
• A cell in a hypertonic
solution:
– loses water
– shrinks (crenation of red blood
cells)
Crenation
33
Figure 3–17c
KEY CONCEPT
• Concentration gradients tend to even out
• In the absence of membrane, diffusion
eliminates concentration gradients
• When different solute concentrations exist
on either side of a selectively permeable
membrane, osmosis moves water through
the membrane to equalize the concentration
gradients
34
How would a decrease in the concentration of
oxygen in the lungs affect the diffusion of
oxygen into the blood?
A. decrease in molecule size results in
decreased diffusion
B. decrease in distance results in increased
diffusion
C. increase in electrical forces results in
increased diffusion
D. decrease in gradient size results in
decreased speed of diffusion
35
Some pediatricians recommend the use of a
10% salt solution to relieve congestion for
infants with stuffy noses.
What effect would such a solution have on the
cells lining the nasal cavity, and why?
A. Cells will lose water because this is a
hypertonic solution.
B. Cells will lose water because this is a
hypotonic solution.
C. Cells will gain water because this is a
hypertonic solution.
D. Cells will gain water because this is a
hypotonic solution.
36
Carrier-Mediated Transport
• Carrier-mediated transport of ions and
organic substrates:
– facilitated diffusion (No energy needed)
– active transport (Energy is needed)
37
Characteristics of
Carrier-Mediated Transport
• Specificity:
– 1 transport protein, 1 set of substrates
• Saturation limits:
– rate depends on transport proteins, not
substrate (same as enzymatic reactions)
• Regulation:
– cofactors such as hormones
38
Carrier-Mediated Transport
• Cotransport
– 2 substances move in the same direction
at the same time
• Countertransport
– 1 substance moves in while another moves
out
39
Facilitated Diffusion
• Passive, Carrier mediated
• Carrier proteins transport molecules too
large to fit through channel proteins
(glucose, amino acids):
– molecule binds to receptor site on carrier protein
– protein changes shape, molecules pass through
– receptor site is specific to certain molecules
40
Figure 3–18
Active Transport
• Active transport proteins:
– move substrates against concentration
gradient
– require energy, such as ATP
– ion pumps move ions (Na+, K+, Ca+, Mg2+)
– exchange pump countertransports 2 ions
at the same time
41
Active Transport, Carrier Mediated
• E.g. Sodium-Potassium Exchange Pump
– 3 Na+ out
– 2 K+ in
– 1 ATP Moves 3 Na+
EXTRACELLULAR FLUID
3 Na+
• 40% cell ATP
Sodium—
potassium
exchange
pump
2 K+
ATP
ADP
42
CYTOPLASM
Secondary Active Transport
• Na+ concentration gradient drives
glucose transport
• ATP energy pumps Na+ back out
Cotransport
Countertransport
43
Figure 3–20
Transport Vesicles
• Also called bulk transport
• Vesicles:
– endocytosis (endo = into)
– active transport using ATP:
• receptor-mediated
• pinocytosis
• phagocytosis
– exocytosis (exo = out of)
44
Receptor-Mediated Endocytosis
45
Figure 3–21
Receptor-Mediated Endocytosis
• Receptors (glycoproteins) bind target
molecules (ligands)
• Coated vesicle (endosome) carries
ligands and receptors into the cell
46
Pinocytosis
• Pinocytosis (cell drinking)
• Endosomes “drink” extracellular fluid and
enclose it in membranous vesicles at the
cell surface
– Similar to the steps in receptor-mediated
endocytosis, except that ligand binding is not
the trigger
47
Figure 3–22a
Phagocytosis
• Phagocytosis (cell eating)
– pseudopodia (psuedo = false,
podia = feet)
– engulf large objects in
phagosomes
48
Figure 3–22b
Exocytosis
• Is the reverse of endocytosis
49
Figure 3–7b
Summary
The 7 methods of transport
50
Table 3–3
Transmembrane potential
51
Electrical Charge
• Selective permeability of membrane allows
different concentrations of molecules in/outside
cells
• Cell membrane
– Inside cell: slightly negative
• due to the abundance of proteins
– Outside cell: slightly positive
• due to cations in extracellular fluids
• Phospholipids hold charges apart creating a
transmembrane potential
– Unequal charge across the cell membrane
• Resting potential ranges from
– 10 mV to —100 mV, depending on cell type
52
During digestion in the stomach, the
concentration of hydrogen ions (H+) rises to
many times that in cells of the stomach.
Which transport process could be responsible?
A.
B.
C.
D.
facilitated diffusion
osmosis
active transport
endocytosis
53
During digestion in the stomach, the
concentration of hydrogen ions (H+) rises to
many times that in cells of the stomach.
Which transport process could be responsible?
A.
B.
C.
D.
facilitated diffusion
osmosis
active transport
endocytosis
54
If the cell membrane were freely permeable
to sodium ions (Na+), how would the
transmembrane potential be affected?
A. it would move closer to zero
B. it would become more positive
C. it would become more
negative
D. it would become unstable
55
When they encounter bacteria, certain
types of white blood cells engulf the
bacteria and bring them into the cell.
What is this process called?
A.
B.
C.
D.
pseudocytosis
exocytosis
pinocytosis
phagocytosis
56
Increase Surface Area: Microvilli
• Surface area of membrane can be increased
by microvilli
– For absorption or secretion
• Microvilli: ‘fingers’ of cell membrane
containing a web of microfilaments and
cytoplasm, anchored to cytoskeleton
57
2. Cytoplasm
• Material enclosed by plasma membrane
• Occupies space between plasma membrane and
nuclear membrane
• Components:
– cytosol (fluid):
• High K+, low Na+
• Colloid Solution: proteins and enzymes
• Nutrient Reserves: carbohydrates, lipids, and amino acids
– Inclusions:
• Type and number varies with cell
• E.g. glycogen, melanin, steroids, etc.
– organelles:
•
•
•
•
Carry out cellular functions
Each has separate function
Some have membranes
Some free in cytosol
58
Cell organelles
and their functions
59
Types of Organelles
• Nonmembranous organelles:
– no membrane
– direct contact with cytosol
• Membranous organelles:
– covered with plasma membrane
– isolated from cytosol
60
Nonmembranous Organelles
• 6 types of nonmembranous organelles:
–
–
–
–
–
–
cytoskeleton
Microvilli
centrioles
cilia
ribosomes
proteasomes
61
3. The Cytoskeleton
• Structural proteins for shape and
strength (Internal Framework)
• 4 types of filaments
–
–
–
–
Microfilaments
Intermediate filaments
Thick filaments
Microtubules
62
Figure 3–3a
A. Microfilaments
•
•
•
•
Thin filaments (<6nm diameter)
Composed of the protein actin
Usually at periphery of the cell
Functions:
– provide additional strength by attaching the
membrane to the cytoplasm
– Attach integral proteins to cytoskeleton
– Pairs with thick filaments of myosin for muscle
movement
63
Intermediate Filaments & Thick
Filaments
B. Intermediate Filaments:
– 7-11 nm diameter
• Mid-sized between microfilaments and thick filaments
– Durable, type varies with cell (collagen, elastin,
keratin)
– Functions:
• strengthen cell and maintain shape
• stabilize position of organelles
• stabilize the cell relative to other cells
C. Thick Filaments
–
–
–
–
15 nm diameter
Composed of myosin
Muscle cells only
Function
• Interact with actin to produce movement
64
D. Microtubules
•
•
•
•
Large (25nm diameter), hollow tubes
Composed of tubulin protein
Originate from centrosome
Functions:
– Foundation of the cytoskeleton
– Allows the cell to change shape and assists in mobility
– Involved in transport
• Molecular motors travel along microtubule “tracks”
• move vesicles within cell
– Makes up the spindle apparatus for nuclear division
(mitosis)
– The structural part of some organelles
• Centrioles, cilia, flagella
65
4. Centrioles in the Centrosome
Centrioles :form spindle
apparatus during cell division
Centrosome: cytoplasm
surrounding centriole near the
nucleus
– Consists of matrix and paired
centrioles
– Functions as microtubule
organizing center
– Responsible for assembling
spindle apparatus during mitosis
66
Figure 3–4a
5. Cilia and Flagella
• Hair like projections
• Contain a microtubule core
with cytoplasm covered in
plasma membrane
• Anchored in the cytosol by
basal bodies
• Cilia: Short, numerous
– Function: sweep substances
over cell surface
• Flagella: Long, singular
– Function: propel cell through
environment
67
Figure 3–4b,c
6. Ribosomes
• Site of protein synthesis (polypeptide
formation)
• Two subunits composed of rRNA & protein:
– free ribosomes in cytoplasm:
• Manufacture proteins for use in cytoplasm
– fixed ribosomes attached to Endoplasmic
reticulum:
• Manufacture proteins for export or use in
membrane
68
Cells lining the small intestine have
numerous fingerlike projections on their free
surface. What are these structures, and
what is their function?
A. microvilli; move substances across
cell surface
B. microvilli; increase cell’s surface area
and absorptive ability
C. cilia; increase cell’s surface area and
absorptive ability
D. cilia; move substances across cell
surface
69
Membranous Organelles
• 5 types of membranous organelles:
–
–
–
–
–
endoplasmic reticulum (ER)
Golgi apparatus
lysosomes
peroxisomes
mitochondria
70
7. Endoplasmic Reticulum (ER)
Location:
- Attached to the
Nuclear
Envelope
71
Figure 3–5a
Endoplasmic Reticulum (ER)
• endo = within, plasm = cytoplasm, reticulum =
network
• Cisternae are storage chambers within
membranes
• Function:
–
–
–
–
Synthesis of proteins, carbohydrates, and lipids
Storage of synthesized molecules and materials
Transport of materials within the ER
Detoxification of drugs or toxins
72
Smooth Endoplasmic
Reticulum (SER)
• No ribosomes attached
• Tubular Membrane
• Functions:
–
–
–
–
–
Lipid metabolism (synthesis, breakdown, transport)
Synthesis of steroid hormones (reproductive system)
Detoxification of drugs
Breakdown of glycogen (storage in muscles) to glucose
Store ions (e.g. Ca2+)
73
Rough Endoplasmic
Reticulum (RER)
• Surface covered with ribosomes:
• Ribosomes synthesize proteins and feed
them into RER cisternae to be modified
– E.g. +carbs = glycoprotein
• Modified proteins are put into transport
vesicles to go to Golgi
• These proteins for exocytosis or use in
membrane
74
Golgi Apparatus
• Stack of cisternae
with associated
transport vesicles
• Near nucleus but
not attached
• Function:
– Modify, concentrate,
and sort export
proteins
75
Figure 3–6a
Golgi Apparatus
• Transport vesicles from
RER dock on cis (forming)
face of golgi and release
contents into golgi
• Proteins (and
glycoproteins) are
modified
– Phosphate, carbs, or lipids
attached
• Proteins transit between
cisternae via vesicles from
cis face (forming) to trans
face (maturing)
76
Vesicles of the Golgi Apparatus
• At trans face, proteins are packaged into:
– Secretory vesicles:
• modify and package products for exocytosis
– Membrane renewal vesicles:
• Carry products to membrane
– Lysosomes:
• Membrane bound sacs of digestive enzymes
77
Exocytosis
• Ejects secretory products and wastes
78
Figure 3–7b
9. Lysosomes
• Powerful enzyme-containing vesicles:
– lyso = dissolve, soma = body
• Digestion centers for large molecules or structures
• Endosomes or phagosomes containing endocytosed things, and
organelles targeted for destruction are fused with lysosome and
broken down
• Some solutes diffuse into cytoplasm for use, remaining debris
are exocytosed
79
Figure 3–8
Lysosome Structures and Function
• Primary lysosome:
– formed by Golgi and inactive enzymes
• Secondary lysosome:
– lysosome fused with damaged organelle
– digestive enzymes activated
– toxic chemicals isolated
• Functions:
– Clean up inside cells:
•
•
•
•
break down large molecules
Attack bacteria
recycle damaged organelles
ejects wastes by exocytosis
80
Autolysis
• Self-destruction of damaged cells:
–
–
–
–
–
auto = self, lysis = break
lysosome membranes break down
digestive enzymes released
cell decomposes
cellular materials recycle
81
Tay Sach’s Disease
• Caused by lysosomes that fail to break
down glycolipids in nerve cells
• Accumulation of glycolipids disrupts
nerve function
• Progressive mental retardation
• Death by age 18 months
82
10. Peroxisomes
• Are enzyme-containing vesicles:
– break down fatty acids
– Membrane sacs containing oxidases and
catalases to neutralize free radicals that are
formed during catabolism of organic
molecules
• produce hydrogen peroxide (H2O2)
– Peroxisomes not made by golgi
• appear to self replicate
83
11. Proteasomes
• Cylindrical structure composed of
protein digesting enzymes (proteases)
• Disassemble damaged proteins for
recycling
– E.g. degrade proteins tagged with
ubiquitin to recycle amino acids
84
KEY CONCEPT
• Cells: basic structural and functional
units of life
– respond to their environment
– maintain homeostasis at the cellular level
– modify structure and function over time
85
12. Mitochondrion Structure
• Sausage-shaped with double membrane
– Outer membrane: Smooth
– Inner membrane: folded into cristae
– Center: matrix
86
Figure 3–9a
Mitochondrial Function:
Power House of the Cell
• Aerobic respiration occurs on surface of cristae
– takes chemical energy from food (glucose)
– With the use of oxygen, Glucose is catabolized
creating CO2 waste to convert ADP into ATP
• Mitochondria supply most of cell’s energy
• Have their own DNA (maternal)
• Can replicate independent of the cell
glucose + oxygen + ADP
carbon dioxide + water + ATP
87
Figure 3–9b
KEY CONCEPT
• Mitochondria provide cells with energy
for life:
– require oxygen and organic substrates
– generate carbon dioxide and ATP
88
Certain cells in the ovaries and testes
contain large amounts of smooth
endoplasmic reticulum (SER). Why?
A. to produce large amounts of
proteins
B. to digest materials quickly
C. to store large amounts of
hormones
D. to produce large amounts of
steroid hormones
89
What does the presence of many
mitochondria imply about a cell’s
energy requirements?
A. a high demand for energy
B. a low demand for energy
C. fluctuating energy needs
requiring flexibility
D. number of mitochondria provides
no implication of energy needs
90
How the nucleus
controls the cell
91
13. The Nucleus
• Is the cell’s control center
• Contains DNA: genetic material
• Most cells have one, exceptions:
– Skeletal muscle (many), RBCs (none)
92
Figure 3–10a
Structure of the Nucleus
• Nucleus:
– largest organelle
• Nuclear envelope:
– double membrane around the nucleus,
connected to ER
• Nuclear pores with regulator proteins:
– Control exchange of materials between
cytoplasm and nucleus
93
Within the Nucleus
• Nucleoplasm:
– fluid containing ions, proteins
(enzymes), DNA, RNA, and
nucleoli
• Nucleoli: Dark areas
– site of rRNA synthesis and
packaging into ribosomal
subunits
• In non-dividing cells DNA is
loose
– Called chromatin
94
Organization of DNA
• DNA in chromatin is
organized into
Nucleosomes:
– DNA coiled around
histones
• During Nuclear Division,
Chromatin is tightly
coiled into visible
chromosomes (23 pairs
in humans)
• Chromosomes:
– tightly coiled DNA (cells
dividing)
95
Figure 3–11
The Genetic Code
96
DNA and Genes
• DNA: contains genes
– instructions for every protein in the body
• Gene: functional units of heredity
– DNA instructions for a product: RNA or protein
• Humans have 30-75 thousand potential genes (only
1.5% of total DNA)
– Remainder is involved with control of genes or
appear to be junk (25%)
– Noncoding parts of DNA (non-genes) is highly
variable from one person to the next
– Variability allows for identification of an individual
97
by DNA fingerprinting
Gene Activation
• In order for a gene to be expressed
(used to make a product) it must be
unwound from the histone proteins so
it can be read
• Disassembly of the nucleosomes and
unwinding of the DNA is called gene
activation
98
Genetic Code
• The chemical language of DNA
instructions:
– Read off a gene in order to assemble a
protein
– sequence of bases (A, T, C, G)
– triplet code:
• 3 bases of DNA = 1 amino acid (codon)
– A gene = all the codons for all the amino
acids in one protein in the correct order
99
Gene Structure and Expression
• Structure
Promoter
Start
Codon
Open Reading Frame
Terminator
Stop
Codon
• Expression
(original)
(copy)
(product)
DNA
RNA
Protein
100
Transcription
Translation
KEY CONCEPT
• The nucleus contains chromosomes
• Chromosomes contain DNA
• DNA stores genetic instructions for
proteins
• Proteins determine cell structure and
function
101
How DNA instructions become
proteins
102
Protein Synthesis
• Transcription:
– copies instructions from DNA to mRNA (in
nucleus)
• Translation:
– ribosome reads code from mRNA (in
cytoplasm)
– assembles amino acids into polypeptide chain
• Processing:
– by RER and Golgi apparatus produces protein
103
mRNA Transcription
• A DNA gene is transcribed to mRNA in 3
steps:
– gene activation
– DNA to mRNA
– RNA processing
104
mRNA Transcription
DNA
STEP
Gene
G
C
A
T
A
T
T
A
G
C
A
T
G
C
T
A
A
T
C
G
G
C
G
C
C
G
T
A
C
G
G
C
A
T
T
A
T
A
Template
strand
STEP
G
C
A
RNA
polymerase
A
T
Promoter
Coding
strand
Triplet 1
G
G
G
A
G
2
C
G
C
C
C
G
C
C
T
A
3
T
T
C
C
A
4
Codon 4
(stop codon)
•
T
G
A
Codon
1
G
G
G
Triplet 4
2
Codon
3
C
C
C
Codon
2
T
1
mRNA
strand
U
T
A
G
Triplet 3
A
G
C
Triplet 2
Codon
1
A
A
A
C
G
G
T
STEP
T
T
RNA
nucleotide
KEY
A
Adenine
G
Guanine
C
Cytosine
U
Uracil (RNA)
T
Thymine
105
Step 1: Gene Activation
• Uncoils DNA, removes histones
• Start (promoter) and stop codes on
DNA mark location of gene:
– coding strand is code for protein
– template strand used by RNA polymerase
molecule
106
Step 2: DNA to mRNA
• Enzyme RNA polymerase transcribes
DNA:
– binds to promoter (start) sequence
– reads DNA code for gene
– binds nucleotides to form messenger RNA
(mRNA)
– mRNA duplicates DNA coding strand,
uracil replaces thymine
107
Step 3: RNA Processing
• At stop signal, mRNA detaches from
DNA molecule:
–
–
–
–
code is edited (RNA processing)
unnecessary codes (introns) removed
good codes (exons) spliced together
triplet of 3 nucleotides (codon) represents
one amino acid
108
Codons
109
Table 3–2
Key Concept
• The timing of gene activation
(transcription) for any gene is
controlled by signals from outside the
nucleus, either from within the cell or
in response to external cues
– E.g. Hormones
110
Translation
• Making a protein using
the mRNA blueprint
• Occurs in the cytoplasm
on free ribosomes or on
fixed ribosomes on the
RER
• mRNA moves:
– from the nucleus
– through a nuclear pore
111
Figure 3–13
Translation
STEP
STEP
NUCLEUS
mRNA
The mRNA strand binds to the small
ribosomal subunit and is joined at the
start codon by the first tRNA, which
carries the amino acid methionine.
Binding occurs between complementary
base pairs of the codon and anticodon.
1
KEY
A Adenine
Small
ribosomal
subunit
•tRNA delivers amino
acids to mRNA
2
1
tRNA
Anticodon
tRNA binding sites
G Guanine
C
Amino acid
The small and large ribosomal subunits
interlock around the mRNA strand.
U A C
Cytosine
U Uracil
Start codon
mRNA strand
Large
ribosomal
subunit
112
Translation
STEP
STEP
A second tRNA arrives at the adjacent
binding site of the ribosome. The
anticodon of the second tRNA binds to
the next mRNA codon.
1
STEP
The first amino acid is detached from its
tRNA and is joined to the second amino
acid by a peptide bond. The ribosome
moves one codon farther along the
mRNA strand; the first tRNA detaches
as another tRNA arrives.
Peptide bond
2
1
The chain elongates until the stop
codon is reached; the components
then separate.
Small ribosomal
subunit
3
2
1
Stop
codon
U A C
A U G
Completed
polypeptide
2
3
G G C
C C G A G
C C G A G C U
Large
ribosomal
subunit
A
113
Genetic Code
114
Examples using the Genetic Code:
Coding Strand DNA:
ATgCAgTTTACgCAgAAgATCAgTTAg
Template strand DNA: complement A-T, C-G
TACgTCAAATgCgTCTTCTAgTCAATC
Transcription to form mRNA:
complementary base pairing to template, U replaces T
AUgCAgUUUACgCAgAAgAUCAgUUAg
Translation to form protein: read codons from genetic code
e.g. AUg = Met/Start (start codon)
Aug/CAg/UUU/ACg/CAg/AAg/AUC/AgU/UAg
Met-Gln-Phe-Thr-Glu-Lys-Ile-Ser
UAg = stop codon (no tRNA, no amino acid)
115
Mutations
• Most non-infectious disease, conditions, and disorders are
due to mutations in the DNA that change the amino acids in
the protein
– E.g. sickle cell anemia
• Point mutation in DNA: A  T
• Changes on codon: GAG  GTG
• Changes one amino acid:
– Glutamic acid (-charge)  valine (neutral)
• This alters the 3D shape of the whole hemoglobin
protein: globular  fibrous
• Which changes the shape of the red blood cell:
– Disc  crescent
• Which prevents the RBC from carrying oxygen, and
116
causes it to block capillaries
Mutations
• Point mutations = change in 1 base of DNA can
be a silent mutation if the amino acids is not
changed
– common at the 3rd base in a codon
• Insertion mutation = addition of a base which
changes the reading frame;whole protein after
the mutation is wrong
• Deletion Mutation = removal of a base, alter
reading frame, protein wrong.
117
KEY CONCEPT
• Genes:
– are functional units of DNA
– contain instructions for 1 or more proteins
• Protein synthesis requires:
– several enzymes
– ribosomes
– 3 types of RNA
• Mutation is a change in the nucleotide sequence of a
gene:
– can change gene function
• Causes:
– exposure to chemicals
– exposure to radiation
– mistakes during DNA replication
118
How does the nucleus control the
activities of a cell?
A.
B.
C.
D.
through nuclear pores
through the nuclear matrix
through DNA
through RNA
119
What process would be affected by
the lack of the enzyme RNA
polymerase?
A. nothing would be affected; DNA
polymerase would take over
B. cell’s ability to duplicate DNA
C. cell’s ability to translate DNA
D. cell’s ability to transcribe RNA
120
How cells reproduce
121
Cell Life Cycle
• Life span of cell depends on type of cell
• All cells eventually die
– Apoptosis: controlled cell death, lysosomes are
defused
• Some cells must divide to make cells to
replace dying cells; function of stem cells
• To divide, DNA must be replicated and equally
distributed between the stem cell and new
daughter cell
122
Figure 3–3
Interphase
• Most of a cell’s life is spent in a nondividing
state (interphase)
– Period of time that a cell performs its normal
functions
• The nondividing period:
– G-zero phase—specialized cell functions only
• If a cell never divides
• Cells preparing for dividing, will go through 3
stages
– G1 phase—cell growth, organelle duplication,
protein synthesis, synthesizes enough cytoplasm
for 2 cells
– S phase—DNA replication and histone synthesis
– G2 phase—finishes protein synthesis and centriole
replication
123
3 Stages of Cell Division
• Body (somatic) cells divide in 3 stages:
– DNA replication duplicates genetic
material exactly
– Mitosis divides genetic material equally
– Cytokinesis divides cytoplasm and
organelles into 2 daughter cells
124
DNA Replication
125
DNA Replication
• DNA helicases unwind the DNA and separates the strands
• DNA polymerase bind to the DNA and synthesizes
complementary antiparallel strands
– DNA polymerase only add to the 3’ end of the molecule
• Leading strand: synthesized continuously
• Lagging strand: synthesized in pieces called Okasaki
fragments
– Okasaki fragments are attached end to end into
one strand by DNA Ligase
• DNA rewinds into double helix molecules
– New molecules contains one strand of the original DNA
and one newly synthesized strand
126
Figure 3–24
Overview of Cell Life Cycle
INTERPHASE
S
DNA
replication,
synthesis
of
histones
G1
Normal
cell functions
plus cell growth,
duplication of
organelles,
protein
synthesis
G2
Protein
synthesis
THE
CELL
CYCLE
M
Indefinite period
G0
Specialized
cell functions
MITOSIS
(See Figure 3-25)
127
Mitosis
• Mitosis (nuclear division) divides
duplicated DNA into 2 sets of
chromosomes:
– DNA coils tightly into chromatids
– chromatids connect at a centromere
– protein complex around centromere called
the kinetochore
• Followed by cytokinesis:
– Separation of the cells
128
Stage 1: Prophase
• Nucleoli disappear
• Centriole pairs move to
cell poles
• Microtubules (spindle
fibers) extend between
centriole pairs
• Nuclear envelope
disappears
• Spindle fibers attach to
kinetochore
129
Figure 3–25 (Stage 1)
Stage 2: Metaphase
• Chromosomes align
in a central plane
(metaphase plate)
130
Figure 3–25 (Stage 2)
Stage 3: Anaphase
• Microtubules pull
chromosomes apart
• Daughter
chromosomes
groups near
centrioles
131
Figure 3–25 (Stage 3)
Stage 4: Telophase
• Nuclear membranes
reform
• Chromosomes uncoil
• Nucleoli reappear
• Cell has 2 complete
nuclei
132
Figure 3–25 (Stage 4, 1 of 2)
Overview of Mitosis
133
KEY CONCEPT
• Mitosis duplicates chromosomes in the
nucleus for cell division
134
Stage 4: Cytokinesis
• Division of the cytoplasm
• Cleavage furrow around metaphase plate
• Membrane closes, producing daughter cells
135
Figure 3–25 (Stage 4, 2 of 2)
What regulates cell division
136
Mitotic Rate and Life Span
• Rate of cell division:
– slower mitotic rate means longer cell life
– cell division requires energy (ATP)
• Cell Life Span:
– Muscle cells, neurons rarely divide
– Exposed cells (skin and digestive tract)
live only days or hours
137
Regulating Cell Life
• Normally, cell division balances cell loss
• Increases cell division:
– internal factors (MPF)
– extracellular chemical factors (growth
factors)
• Decreases cell division:
– repressor genes (faulty repressors cause
cancers)
– worn out telomeres (terminal DNA segments)
138
Chemicals Controlling
Cell Division
139
Table 3–4
A cell is actively manufacturing enough
organelles to serve two functional cells.
This cell is probably in which phase of its
life cycle?
A.
B.
C.
D.
S
G1
G2
M
140
During DNA replication, a nucleotide is
deleted from a sequence that normally codes
for a polypeptide. What effect will this
deletion have on the amino acid sequence of
the polypeptide?
A. no effect, deletion will be skipped
B. no effect, deletion will be
automatically repaired
C. amino acid sequence will disintegrate
D. the amino acid sequence would be
altered
141
What would happen if spindle fibers
failed to form in a cell during mitosis?
A. centromeres would not appear
B. nuclear membrane would not
disintegrate
C. chromosomes would not
separate
D. chromatin would not condense
142
Cancer
• Cell division: controlled by internal and external
factors
– In adult cell growth = cell death
– If growth exceeds death a tumor can form
• Cancer:
– illness that disrupts cellular controls
– produces malignant cells
143
Cancer
• Benign tumors:
– grow in a connective tissue capsule and
remain in one place
• Malignant tumor: ignore growth control
mechanisms
– spread into surrounding tissues (invasion)
– start new tumors (metastasis)
• Cancer develops in steps:
1. abnormal cell
2. primary tumor
3. metastasis
4. secondary tumor
144
Cancer
• Cancer: caused by mutation in a growth control gene
(oncogene = mutated genes that cause cancer)
– 1° tumor: cells grow uncontrolled
– 2° tumor: cells metastasize in blood and lymph to establish new
growth elsewhere
• Tumors trigger growth of blood vessels to support the cells
– In order for diffusion to bring nutrients and remove wastes all cells
have to be within 125µm of a vessel
• Eventually the tumor will crowd out normal tissues causing
organ failure
145
Figure 3–26
KEY CONCEPT
• Mutations disrupt normal controls over
cell growth and division
• Cancers often begin where stem cells
are dividing rapidly
• More chromosome copies mean greater
chance of error
146
Cell Differentiation
147
What is cell differentiation?
• Cells specialize or differentiate:
– All somatic cells in the body have the same DNA but
different sizes, shapes, and functions
– As cells specialize to become a specific cell type many
genes get turned off permanently, cells are considered
differentiated
– Differentiated cells only express genes related to their
function
– Stem cells are undifferentiated:
• Embryonic stem cells can express all of their genes and become
any cell type
• Other stem cells can express most of their genes
– All stem cells do not show many specialized functions
and can differentiate into many types of tissue
148
KEY CONCEPT
• All body cells, except sex cells, contain
the same 46 chromosomes
• Differentiation depends on which genes
are active and which are inactive
149
SUMMARY
• Structures and functions of human cells
• Structures and functions of membranous and
nonmembranous organelles
• ATP, mitochondria, and the process of
aerobic cellular respiration
• Structures and functions of the nucleus:
– control functions of nucleic acids
– structures and replication of DNA
– DNA and RNA in protein synthesis
150
SUMMARY
• Structures and chemical activities of the cell
membrane:
–
–
–
–
diffusion and osmosis
active transport proteins
vesicles in endocytosis and exocytosis
electrical properties of plasma
• Stages and processes of cell division:
– DNA replication
– mitosis
– cytokinesis
• Links between cell division, energy use, and
cancer
151
Homework
Lecture
• Study Chapter 1, 2, and 3 for Exam #1
• Complete Homework #1
Laboratory
152