Transcript Chapter 4

Chapter 4
Physiology of Cells
Sean Ragain
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Slide 1
Movement of Substances through
Cell Membranes (Table 4-1)
• Passive transport –
does not require any
energy (ATP)
expenditure of the
cell; substances
move from high
concentration to low
concentration
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Slide 2
Movement of Substances
through Cell Membranes
• Two types of passive
transport

Diffusion – molecules move
through the membrane from
high concentration to low
• As molecules diffuse, a state
of equilibrium will occur

Osmosis – Diffusion of water
through a selectively
permeable membrane
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Slide 3
Osmosis
• Diffusion of water through a selectively
permeable membrane, which limits the diffusion
of at least some of the solute particles
• Water pressure that develops as a result of
osmosis is called osmotic pressure
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Slide 4
Osmosis
• Isotonic—two fluids that
have the same potential
osmotic pressure (Figure 45)
• Hypertonic—“higher
pressure”; cells placed in
solutions that are hypertonic
to intracellular fluid always
shrivel as water flows out of
cell
• Hypotonic—“lower
pressure”; cells placed in a
hypotonic solution may swell
as water flows into them
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Slide 5
Facilitated Diffusion (mediated
passive transport)
• A special kind of
diffusion whereby
movement of molecules
is made more efficient
by the action of
transporters embedded
in a cell membrane
• Transports substances
down a concentration
gradient
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Slide 6
Movement of Substances
through Cell Membranes
• Active transport – requires the
expenditure of metabolic energy by the
cell – REQUIRES ATP

Transport by pumps
• Pumps are membrane transporters that move a
substance against its concentration gradient –
the opposite of diffusion
• Examples: calcium pumps (Figure 4-8) and
sodium-potassium pumps (Figure 4-9)
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Slide 7
Calcium Pumps
• In the membranes of
muscle cells – allow the
cell to force nearly all
intracellular calcium ions
into special compartments
or out of the cell entirely

Muscle cells can not
function properly if calcium
ion concentrations are not
kept low during rest
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Slide 8
Sodium Potassium Pumps
• Operates in the membranes
of all human cells
• Essential for cell survival
• Transports sodium ions out
and potassium ions into the
cell

Creates a gradient of
sodium and potassium ions

Very important in neuron
function and the polarization
of neuronal cells
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Slide 9
Transport by Vesicles
• An active transport processes
• Transport by vesicles – allows substances to
enter or leave the interior of a cell without
actually moving through its plasma
membrane
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Slide 10
Endocytosis
• Endocytosis – the plasma membrane “traps” some extracellular
material and brings it into the cell in a vesicle

Two basic types of endocytosis (Figure 4-10):
• Phagocytosis—“condition of cell-eating”; large particles are
engulfed by the plasma membrane and enter the cell in vesicles;
vesicles fuse with lysosomes, where the particles are digested
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Slide 11
Exocytosis
• An active transport processes
• Process by which large molecules, notably
proteins, can leave the cell even though they are
too large to move out through the plasma
membrane
• Provides a way for new material to be added to
the plasma membrane
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Slide 12
Cell Metabolism
• Metabolism is the set of chemical reactions
in a cell

Catabolism – breaks large molecules into smaller
ones; usually releases energy

Anabolism – builds large molecules from smaller
ones; usually consumes energy
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Slide 13
Enzymes
• Enzymes are proteins that act as chemical catalysts (reduce
activation energy needed for a reaction) and regulate cell
metabolism
• Chemical structure of enzymes

Proteins of a complex shape

Active Site

Cofactors of enzymes include vitamins and
minerals
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Slide 14
General Functions of Enzymes
• Regulating metabolic
pathways
• Most enzymes catalyze
reversible reactions
• Enzymes are
continually destroyed
and are replaced
• Many enzymes are
synthesized as inactive
proenzymes
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Slide 15
Cell Metabolism
• General functions of enzymes (cont.)

Enzymes are continually being destroyed and are
continually being replaced

Many enzymes are first synthesized as inactive
proenzymes – proinsulin
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Slide 16
DNA

Deoxyribonucleic acid
(DNA)
• A double-helix polymer
that functions to transfer
information, encoded in
genes, that directs the
synthesis of proteins
(Figure 4-22)
• Gene – a segment of a
DNA molecule that
consists of approximately
1000 pairs of nucleotides
and contains the code for
synthesizing one
polypeptide (Figure 4-23)
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Slide 17
Cell Metabolism
• Anabolism – begins with reading the “genetic
code”

Protein synthesis is a central anabolic pathway in
cells (Table 4-2)
• Transcription (1)
• Translation (2)

Central Dogma
• DNA
1.
RNA
2.
protein
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Slide 18
Transcription
• Transcription – mRNA
forms along a segment
of one strand of DNA
(Figure 4-24)

Base Pair Rules

A-U, C-G

Occurs in the Nucleus

Be able to transcribe a
segment of DNA
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Slide 19
Translation, Figure 4-26
• mRNA associates with a ribosome in the cytoplasm
• tRNA molecules bring specific amino acids to the mRNA at the
ribosome; the type of amino acid is determined by the fit of a specific
tRNA’s anticodon with mRNA’s codon (Figure 4-27)
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Slide 20
Cell Metabolism
• Anabolism (cont.)

Genome
• The genes of the cell

Proteome
• All the proteins synthesized by a cell make up the
cell’s proteome
• All the proteins synthesized in the whole body are
collectively called the human proteome
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Slide 21
Growth and Reproduction of Cells
• Cell growth – depends on
using genetic information
in DNA to make the
structural and functional
proteins needed for cell
survival
• Cell reproduction –
ensures that genetic
information is passed from
one generation
to the next
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Slide 22
Growth and Reproduction of Cells
• Production of cytoplasm – more cell material
is made, including growth and/or replication
of organelles and plasma membrane

Occurs during Interphase
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Slide 23
DNA replication (Table 4-4)
• Replication of the genome prepares the cell for reproduction;
mechanics are similar to RNA synthesis

DNA strand uncoils and strands come apart
 Along each separate strand, a complementary strand forms

The two new strands are called chromatids, instead of chromosomes
 Chromatids are attached in pairs at the centromere
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Slide 24
Chromosomes
• 23 Pairs of Human Chromosomes
• 46 Total Chromosomes
• 1 set from mother and 1 set from father
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Slide 25
Cell Growth
• Growth phase of the
cell life cycle can be
subdivided into the
first growth phase
(G1),
the [DNA] synthesis
phase (S), and the
second growth phase
(G2)
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Slide 26
Cell Reproduction
• Cell reproduction – cells reproduce by splitting
themselves into two smaller daughter cells (Table 4-5)

Mitosis – the process of organizing and distributing nuclear DNA
during cell division has four distinct phases (Figure 4-31) –
Prophase, Metaphase, Anaphase, Telophase
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Slide 27
Prophase
• Prophase – “before-phase”

Nuclear envelope falls apart as the chromatids coil up to
form chromosomes

As chromosomes are forming, centriole pairs move toward
the poles of the parent cell, spindle fibers are constructed
between them

Nucleolous disappears
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Slide 28
Metaphase
• Metaphase – “position-changing phase”

Chromosomes align along the “middle” of the
mitotic spindle

Each chromatid attaches to a spindle fiber
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Slide 29
Anaphase
• Anaphase – “apart phase”

Centromere of each chromosome split to form two
chromosomes

Each chromosome is pulled apart toward the nearest
pole
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Slide 30
Telophase
• Telophase – “end phase”

DNA uncoils into chromatin

Nucleolous reappears

After completion of telophase, each daughter cell
begins interphase to develop into a mature cell
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Slide 31
Cytokinesis
• Division of the Cytoplasm

Begins in late anaphase and is completed at the
end of telophase
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Slide 32
Meiosis
• Meiosis (Figure 4-32;
see also Figure 33-1)
• Cell Division that occurs
in gametes (sex cells)
• Results in 4 haploid
gametes with 23
chromosomes
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Slide 33
Regulating the Cell Life Cycle
• Cyclin-dependent kinases (CDKs) are activating
enzymes that drive the cell through the phases of
its life cycle
• Cyclins are regulatory proteins that control the
CDKs and “shift” them to start the next phase
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Slide 34
Cycle of Life: Cells
• Different types of cells have different life
cycles
• Advancing age creates changes in cell
numbers and in their ability to function
effectively

Examples of decreased functional ability include
muscle atrophy, loss of elasticity of the skin, and
changes in the cardiovascular, respiratory, and
skeletal systems
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Slide 35
The Big Picture: Cells and the Whole Body
• Most cell processes are occurring at the
same time in all of the cells throughout
the body
• The processes of normal cell function
result from the coordination dictated by
the genetic code
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Slide 36
Mechanisms of Disease
• Cellular Diseases

Cell Transport

Cell Membrane
Receptors

Cell Reproduction

DNA and protein
synthesis

Infections
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Slide 37