Download Human Genetics - Chapter 2

Chapter 2
Cells
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Learning Outcomes
• Explain why it is important to know the cellular
basis of a disease
• Define differentiated cell
• List the four major chemicals in cells
• Describe how organelles interact
• Describe the structure and function of a biological
membrane
• List the components of the cytoskeleton
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Learning Outcomes
•
•
•
•
•
Distinguish between mitosis and apoptosis
Describe the events and control of the cell cycle
List the characteristics of a stem cell
Define stem and progenitor cell
How can the bacteria that live in and on our
bodies affect our health?
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Introducing Cells
• Cellular activities underlie our inherited traits,
quirks, and illnesses
• Understanding genetic diseases can suggest ways
to treat the condition
Figure 2.1
Duchenne muscular
dystrophy - Lack of
dystrophin
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Introducing Cells
• Our bodies include more than 290 cell types
• Somatic (body) cells have two copies of the
genome and are said to be diploid
• Sperm and egg cells have one copy of the genome
and are haploid
• Stem cells can divide to give rise to differentiated
cells and replicate themselves through selfrenewal
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Tissue Types
Figure 2.2
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Types of Cells
• Prokaryotic cells
• Lack a nucleus
• Eukaryotic cells
• Possess a nucleus and
organelles
Figure 2.3
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Domains of Life
• Biologists recognize three broad categories of
organisms
• Archaea and Bacteria - Unicellular prokaryotes
• Eukarya - Includes both unicellular and
multicellular eukaryotes
• Cells of domains contain globular assemblies of
RNA and protein called ribosomes
• Essential for protein synthesis
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Chemical Constituents
• Cells contain four types of macromolecules
Type
Carbohydrates
Examples
Sugars, starches
Functions
•
•
Lipids
Fats, oils
•
•
•
Proteins
•
•
Nucleic Acids
DNA, RNA
Provide energy
Contribute to cell structure
Basis of hormones
Form membranes
Provide insulation, store
energy
Antibodies
Enzymes catalyze
biochemical reactions
Translate genetic information
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Organelles
• Divide labor by partitioning certain areas or
serving specific functions
• Keep related biochemicals and structures close to
one another to interact efficiently
• Functions
• Enable a cell to retain and use its genetic
instructions
• Acquire energy, secrete substances, and dismantle
debris
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Figure 2.4
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The Nucleus
• Prominent organelle
• Surrounded by a layer of nuclear envelope
• Contains:
• Nuclear pores that allow movement of
biochemicals
• Nuclear lamina provides mechanical support and
holds nuclear pores in place
• Nucleolus produces ribosomes
• Other contents - Chromosomes, RNA and
nucleoplasm
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The Nucleus
Figure 2.5
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An Animal Cell
• Surrounded by the plasma membrane
• Contains:
•
•
•
•
Cytoplasm
Stored proteins, carbohydrates, and lipids
Pigment molecules
Other small chemicals
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• Secretion
illustrates how
organelles
function
together to
coordinate the
basic life
functions
Figure 2.6
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Endoplasmic Reticulum (ER)
• Interconnected membranous tubules & sacs
• Winds from the nuclear envelope to the plasma
membrane
• Rough ER contains ribosomes and is involved in
protein synthesis
• Smooth ER does not contain ribosomes and is
important in lipid synthesis
• Proteins exit the ER in membrane-bounded,
saclike organelles called vesicles
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Golgi Apparatus
• Stack of interconnected flat, membrane-enclosed
sacs
• Processing center that adds sugars forming
glycoproteins and glycolipids
• Products are released into vesicles that bud off to
the plasma membrane
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Lysosomes
• Membrane-bound sacs
containing 43 types of
digestive enzymes
• Dismantle bacterial
remnants, worn-out
organelles, and excess
cholesterol
• Engages in autophagy
Figure 2.7
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Lysosomes
• Cells differ in the number of lysosomes they
contain
• Absence or malfunction of an enzyme causes a
lysosomal storage disease
• Tay-Sachs is an inherited disorder
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Peroxisomes
• Sacs with outer membranes studded with several
types of enzymes
• Break down lipids, rare biochemicals
• Synthesize bile acids
• Detoxify compounds from exposure to oxygen
free radicals
• Abundant in liver and kidney cells
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Mitochondria
• Surrounded by two
membranes
• Provide energy by
breaking chemical
bonds that hold
together nutrient
molecules in food
• Freed energy is
stored in adenosine
triphosphate (ATP)
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Figure 2.8
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Biological Membrane
• A phospholipid bilayer
• Phosphate end
(hydrophilic)
• Fatty acid chains
(hydrophobic)
Figure 2.9
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Biological Membrane
• Proteins aboard lipids:
• Contribute to cell’s
identity
• Transport molecules
• Keep out toxins and
pathogens
• Some membrane
proteins form channels
for ions
Figure 2.10
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Plasma Membrane - Cell-to-Cell
Communication
• Molecules that extend from the plasma membrane
are receptors
• Signal transduction
• Molecules form pathways that detect signals from
outside the cell and transmit them inward
• Cellular adhesion
• Plasma membrane helps cells attach to certain
other cells
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Structures and Functions of Organelles
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Cytoskeleton Functions
• Maintain cell shape
• Connect cells to each other
• Transport organelles, cellular contents, and
motor molecules
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Cytoskeleton
• Meshwork of protein
rods and tubules
• Includes three major
types of proteins
• Microtubules
• Microfilaments
• Intermediate
filaments
Figure 2.11
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Figure 2.12
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Cell Division and Death
• Growth, development, maintaining health, and
healing from disease or injury require an intricate
interplay between the rates of:
• Mitosis and cytokinesis - Division of DNA and rest
of the cell
• Apoptosis - Cell death
• Precise, genetically programmed sequence of events
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Figure 2.13
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The Cell Cycle
• The sequence of events
associated with cell
division
Figure 2.14
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Stages of the Cell Cycle - Interphase
•
•
•
•
Prepares for cell division
Replicates DNA and subcellular structures
Composed of G1, S, and G2 phases
Cells may exit the cell cycle at G1 or enter G0, a
quit phase
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Stages of the Cell Cycle - Interphase
• Chromosomes are replicated during S phase prior
to mitosis
• Result in each chromosome consisting of two
copies joined at the centromere
• Proteins forming the mitotic spindle are
synthesized
• Microtubules form centrioles near the nucleus
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Replicated and Unreplicated
Chromosomes
Figure 2.15
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Mitosis - Prophase
•
•
•
•
DNA coils tightly
Microtubules organize into a spindle
Nuclear membrane breaks down
Nucleolus is not visible
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Mitosis - Metaphase
• Chromosomes attach to
the spindle at their
centromeres
• Align along the cell’s
equator
• Chromosomes are pulled
with equal force on both
sides
Figure 2.16
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Mitosis - Anaphase
• Centromeres divide
• Chromatids separate and
become independent
chromosomes
• Move to opposite ends of
the cell
Figure 2.16
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Mitosis - Telophase
• Spindle falls apart
• Nucleoli and membranes
around the nuclei re-form
at each end of the elongated
cell
Figure 2.16
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Mitosis - Cytokinesis
• Cytoplasmic division occurs after nuclear
division is complete
• Organelles and macromolecules are distributed
between the two daughter cells
• Microfilament band contracts, separating the two
cells
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Cell Cycle Control
• Checkpoints ensure that chromosomes are
replicated and apportioned into daughter cells
• Internal and external factors can affect a cell’s
mitotic clock
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Cell Cycle Control
Figure 2.17
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Telomeres
• Located at the ends of the chromosomes
• Contain hundreds to thousands of repeats of a 6base DNA sequence
• Lose 50-200 endmost bases after each cell
division
• After 50 divisions, shortened telomeres signal the
cell to stop dividing
• Sperm, eggs, bone marrow, and cancer cells
produce telomerase that prevent shortening of
telomeres
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Figure 2.18
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Hormones and Growth Factors
• Hormone is made in a gland and transported in
the bloodstream to another part of the body
• Exerts a specific effect
• A growth factor acts locally
• Epidermal growth factor (EGF) stimulates cell
division in the skin beneath a scab
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Apoptosis
• Begins when a cell receives a “death receptor”
• Killer enzymes called caspases are activated
• Destroy cellular components
• Phagocytes digest the remains
• Dying cell forms bulges called blebs
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Figure 2.19
• Mitosis and apotosis work together
to form functional body
• Cancer can result from too much
mitosis or too little apotosis
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Stem Cells
• A stem cell divides by
mitosis
• Produces two daughter
cells or a stem cell and a
progenitor cell, which
may be partially
specialized
• Progenitor cells do not
have the capacity of selfrenewal
Figure 2.20
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Stem Cells
• Cells differentiate down cell lineages of stem,
progenitor, and increasingly differentiated cells
• Stem cells and progenitor cells are described in
terms of their developmental potential
• Totipotent - Can give rise to every cell type
• Pluripotent - Have fewer possible fates
• Multipotent - Have only a few developmental
choices
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Figure 2.21
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Stem Cells in Health Care
• There are 3 general sources of human stem cells
• Embryonic stem cells - Created in a lab dish using
the inner cell mass (ICM) of an embryo
• Induced pluripotent stem (iPS) cells - Somatic
cells reprogrammed to differentiate into any of
several cell types
• Adult stem cells - Tissue-specific or somatic stem
cells
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Stem Cells in Health Care
Figure 2.22
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Stem Cell Applications
• Stem cells are being used in four basic ways
• Discovery and development of drugs
• Observing the earliest sign of disease
• Create tissues and organs, for use in implants and
transplants, or to study
• Stimulating stem cells in the body via the
introduction of reprogramming proteins
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The Human Microbiome
• Ninety percent of the cells in a human body are
microorganisms, constitute the human
microbiome
• Different body parts house different communities
of microbes
• Genes interact with the microbiome and with
environmental factors to mold most traits
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