Transcript Human Genetics


Chapter 2 – What abnormality at the cellular
or molecular level lies behind each of the
following disorders? (a) cystic fibrosis (b)
neurofibromatosis and (c) syndactyly.
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Cellular activities and abnormalities underlie
our inherited traits, quirks, and illnesses
Understanding genetic diseases can suggest
ways to treat the condition
Figure 2.1
Lack of
dystrophin
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Our bodies include more than 260 cell types
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Somatic (body) cells have two copies of the
genome and are said to be diploid
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Gametes, sperm and egg cells have one copy
of the genome and are haploid
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Stem cells, which are diploid, can both
replicate themselves and differentiate
themselves for repair and replacement of
specialized cells
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Must maintain basic functions for growth and reproduction,
responding to environment, and utilizing energy.
All cells can be divided
into two main types
Prokaryotic cells
- Lack a nucleus
Eukaryotic cells
- Possess a nucleus
and other organelles
Figure
2.2
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Biologists recognize three broad categories
of organisms based on cellular complexity
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Archaea – extreme bacteria
Eubacteria – more common forms of
bacteria
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Eukarya – Includes both unicellular and
multicellular eukaryotes; higher cells
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The Archaea and Eubacteria are similar in that they are
single-celled organisms, but they differ in certain features of
their RNA and membranes. These cells lack nuclei and other
organelles and therefore are categorized as prokaryotes.
Eukaryotic cells are complex, with abundant and diverse
organelles that compartmentalize biochemical reactions.
Human cells are therefore eukaryotic.
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Cells contain four types of macromolecules
Type
Examples
Functions
Carbohydrates Sugars, starches Energy,
structure
Lipids
Fats, oils
Membranes,
hormones
Proteins
Myosin, collagen Enzymes,
structure
Nucleic Acids DNA, RNA
Genetic
information
Enzymes are proteins that catalyze the multitude of
biochemical reactions that occur in the cell.
The study of nucleic acids is key to the field of genetics.
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An Animal Cell
Surrounded by the plasma membrane
Contains:
- Cytoplasm
- Organelles
- Divide labor by partitioning certain
areas or serving specific functions
Figure 2.3
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An Animal Cell
Figure 2.3
Figure 2.3
The Nucleus
The largest structure in a cell
Surrounded by a double-layered nuclear
envelope
Contains:
- Nuclear pores that allow movement of some
molecules in and out
- Nucleolus, which is the site of ribosome
production
- Chromosomes composed of DNA and
Figure 2.3
proteins
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The Nucleus
Figure 2.4
Figure 2.3
Figure 2.4
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Secretion
illustrates
how
organelles
function
together
to
coordinate
the basic
functions
of life
Figure 2.5
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
Figure 2.3
Golgi Apparatus
Stack of flat membrane-enclosed sacs
Processing center that adds sugars forming
glycoproteins and glycolipids
Site of final protein folding
Products are released into vesicles that bud
off to the plasma membrane
Figure 2.3
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Lysosomes
Membrane-bound sacs
containing > 40 types
of digestive enzymes
Degrade bacteria,
cellular debris, and
nutrients
Tay-Sachs is an
inherited lysosomal
Figure 2.6
storage disorder Figure 2.3
Peroxisomes
Sacs with outer membranes studded with
several types of enzymes that:
Detoxify compounds from free radicals
Break down lipids, rare biochemicals
Synthesize bile acids
Abundant in liver and kidney cells
Figure 2.3
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Mitochondria
Surrounded by two
membranes
Site of ATP (energy)
production
“powerhouse of cell”
Contain their own
circular DNA
Human mitochondrial
DNA is inherited
only from the mother
Figure 2.3
Figure 2.7
Structures and Functions of
Organelles
Table 2.1
Plasma Membrane
Forms a selective
barrier
A phospholipid
bilayer
- Phosphate end
(hydrophilic)
- Fatty acid chains
(hydrophobic)
Figure 2.3
Figure 2.8
Plasma Membrane
Contains proteins,
glycoproteins,
and glycolipids
- Important to cell
function and
interactions
- May be receptors
- Form channels for
ions
FigureFigure
2.3 2.9
Faulty Ion Channels Cause Inherited
Diseases
Sodium channels
- Mutations lead to absence or extreme pain
Potassium channels
- Mutations lead to impaired heart function and
deafness
Chloride channels
- Mutations leadFigure
to cystic
2.3 fibrosis
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Cytoskeleton
A meshwork of
protein rods and
tubules
Includes three major
types of proteins
- Microtubules
- Microfilaments
- Intermediate
filaments
Figure 2.3
Figure 2.10
Cytoskeleton Functions
Maintain cell shape
Connect cells to each other
Transport organelles and small molecules
Provide cell motility (some cell types)
Move chromosomes in cell division
Compose cilia and flagella
Figure 2.3
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▪ Spherocytosis is a heredity defect in the
cytoskeleton of the red blood cell. An
abnormal cytoskeleton protein beneath the
cell membrane and causes the red blood
cells to balloon out, blocking narrow blood
vessels in organs
.
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Cell Division and Death
Normal growth and development require an
intricate interplay between the rates of two
processes
Mitosis – Cell division
- Produces two somatic cells from one
Apoptosis – Cell death
- Precise genetically-programmed sequence
Figure 2.3
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Figure 2.13
Figure 2.12
The Cell Cycle
The sequence of events associated with cell division
G phase: Gap for
growth
S phase: DNA
synthesis
M phase: Mitosis
(nuclear division)
Cytokinesis: Cell
division
Figure 2.3
Figure 2.14
Stages of the Cell Cycle
Interphase
- Prepares for cell division
- Replicates DNA and subcellular structures
- Composed of
G1 – proteins, lipids, & carbs are produced
S – DNA and proteins are made
G2 – more proteins produced
- Cells may exit the cell cycle at G1 or enter G0, a
dormant phase
Mitosis – Division of the nucleus
Cytokinesis – Division
of the2.3
cytoplasm
Figure
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Replication of Chromosomes
Chromosomes are
replicated during
S phase prior to
mitosis
Figure
2.15
The result is two
sister chromatids
held together at
the centromere
Figure 2.3
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Mitosis
Used for growth, repair, and replacement
Consists of a single division that produces
two identical daughter cells
A continuous process divided into 4 phases
- Prophase
- Metaphase
- Anaphase
- Telophase
Figure 2.3
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Mitosis in a Human Cell
Figure 2.15
Figure 2.16
Prophase
Replicated
chromosomes
condense
Microtubules
organize into a
spindle
Nuclear envelope
and nucleolus
break down
Figure
Figure2.3
2.16
Metaphase
Chromosomes line
up on the cell’s
equator or
metaphase plate
Spindle microtubules
are attached to
centromeres of
chromosomes
Figure
Figure2.3
2.16
Anaphase
Centromeres divide
Chromatids separate and
become independent
chromosomes
- They move to opposite
ends of the cell
Figure
Figure2.3
2.16
Telophase
Cell pinches in middle
Chromosomes uncoil
Spindle disassembles
Nuclear envelope reforms
Figure
Figure2.3
2.16
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
Figure 2.3
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Mitosis Animation
Figure 2.3
Cell Cycle Control
Checkpoints ensure that mitotic events
occur in the correct sequence
Internal and external factors are involved
Many types of cancer result from faulty
checkpoints
Figure 2.3
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Cell Cycle Control
Figure 2.17
Figure 2.16
Telomeres
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Located at the ends of the chromosomes
Cellular clock limits number of divisions based
on shrinking telomeres, after about 50 divisions
Crowding, hormones, & growth factors are
extracellular influences on mitosis
Sperm, eggs, bone marrow, and cancer cells
produce telomerase that prevent shortening of
telomeres
Why is this important?
Figure 2.3
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Apoptosis
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Begins when a cell receives a “death
signal”
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Killer enzymes called caspases are
activated
-Destroy cellular components
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Phagocytes digest the remains
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Figure 2.3
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Programmed cell death is part of normal development
Figure 2.19
Mitosis and apotosis work
together to form functional body
Cancer or other disorders can
result from too much mitosis,
too little apotosis
Figure 2.18
Stem Cells
A stem cell divides by
mitosis
- Produces daughter
cells that retain the
ability to divide and
some that specialize
Progenitor cells do
not have the capacity
of self-renewal
Figure 2.3Figure 2.22
Stem Cells
All cells in the human body descend from
stem cells via mitosis and differentiation
Cells differentiate down cell lineages by
differential gene expression
Stem cells are present throughout life and
provide growth and repair
Figure 2.3
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Figure 2.23
Figure 2.3
Stem 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 fates
Figure 2.3
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Stem Cells in Health Care
There are 3 general sources of human stem cells
1) Embryonic stem cells – Created in a lab dish
using the inner cell mass (ICM) of an embryo
2) Induced pluripotent stem (iPS) cells –
Somatic cells reprogrammed to differentiate into
any of several cell types
3) Adult stem cells – Tissue-specific or somatic
stem cells
Figure 2.3
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Stem Cells in Health Care
Figure 2.24
Figure 2.24
Stem Cell Applications
Stem cells are being used in four basic ways
1) Discovery and development of drugs
2) Observing the earliest sign of disease
3) Treatment of disease via implants and
transplants
4) Stimulating stem cells in the body via the
introduction of reprogramming
proteins
Figure 2.3
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Stem Cell Applications
Figure 2.25
Figure 2.3
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