Download Essential knowledge 2.E.1: Timing and coordination of specific

Essential knowledge 2.E.1:
Timing and coordination of specific
events are necessary for the normal
development of an organism, and these
events are regulated by a variety of
mechanisms
Cell Differentiation is…
• the process by which a less specialized cell
becomes a more specialized cell type.
• Differentiation occurs numerous times during
the development of a multicellular organism as
the organism changes from a simple zygote to a
complex system of tissues and cell types.
Cell Differentiation
• Differentiation is a common process in adults as
well: adult stem cells divide and create fully
differentiated daughter cells during tissue repair
and during normal cell turnover.
• Blood cells are derived
through adult stem cells
Observable cell differentiation results
from the expression of genes for
tissue-specific proteins.
• Every cell in our bodies contain our entire
genome, yet on a few genes get expressed.
• Each cell type is defined by the particular genes
that they express.
• Cell differentiation is thus a transition of a cell
from one cell type to another and it involves a
switch from one pattern of gene expression to
another.
Induction of transcription factors(TFs)
during development results in
sequential gene expression.
• Transcription factors are one of the groups of
proteins that read and interpret the genetic
"blueprint" in the DNA.
• They bind to the DNA and help initiate a
program of increased or decreased gene
transcription.
• The regulation of gene target networks by
specific TFs at different stages constitutes the
transcriptional programs that direct cellular
differentiation.
Homeotic genes are involved in
developmental patterns and
sequences.
• Homeotic genes are genes that
determine which parts of the body form
what body parts
• For example, homeotic genes are
involved in determining where, when,
and how body segments develop in flies.
• Alterations in these genes cause
changes in patterns of body parts,
sometimes causing dramatic effects
such as legs growing in place of
antennae or an extra set of wings or, in
the case of plants, flowers with
abnormal numbers of parts.
Embryonic induction in development
results in the correct timing of events.
• Induction is the process by which the presence
of one tissue influences the development of
others.
• Certain tissues, especially in very young
embryos, have the potential to direct the
differentiation of adjacent cells.
• Absence of the inducing tissue results in lack of
or improper development of the induced tissue.
An example of embryonic induction is…
• the development of the eye lens from epidermis
under influence of the eye cup, which grows
toward the skin from the brain.
• As the eye cup comes into contact with any
neighboring epidermis, it transforms that
particular region into a lens.
Temperature and the availability of
water determine seed germination in
most plants.
• Germination is the growth of an embryonic plant
contained within a seed
• Water is required for germination. Mature seeds
are often extremely dry and need to take in
significant amounts of water, relative to the dry
weight of the seed, before cellular metabolism and
growth can resume.
• Temperature affects cellular metabolic and
growth rates. Seeds from different species and even
seeds from the same plant germinate over a wide
range of temperatures.
Genetic mutations can result in
abnormal development.
• To function correctly, each cell depends on
thousands of proteins to do their jobs in the right
places at the right times.
• Sometimes, gene mutations prevent one or more of
these proteins from working properly. By changing a
gene’s instructions for making a protein, a mutation
can cause the protein to malfunction or to be
missing entirely.
• When a mutation alters a protein that plays a critical
role in the body, it can disrupt normal development
or cause a medical condition. A condition caused by
mutations in one or more genes is called a genetic
disorder.
Genetic
Transplantation
• Genetic transplantation
experiments support the link
between gene expression and
normal development.
• John Gurdon transplanted
nuclei from a tadpole cell into
eggs from which the nuclei had
been removed.
• This indicates that the nuclei
of cells in later stages of
development retain genetic
information necessary to
direct development of all other
cells in an individual.
Genetic regulation by microRNAs plays an
important role in the development of organisms
and the control of cellular functions.
• MicroRNAs - post-transcriptional regulators;
• They are short RNAs, about 22 nucleotides long;
bind to the mRNAs, usually silencing them.
• Wow that is short! Must be why they are called
MicroRNAs!!
• What do they do again?
• That’s right, they bind to mRNAs before they
have time to get translated—This usually silences
them(stops them from translating into a
protein).
Apoptosis
• Programmed cell death (apoptosis) plays a role
in the normal development and differentiation.
• normal development of the fingers and toes
depends on death of the cells forming webs
between them.
Apoptosis and the immune response
• Apoptosis of lymphocytes occurs in order to control
an excessive immune response. When the immune
system is activated, it produces lots of lymphocytes
that work to fight the infection. If this immune
response becomes too extreme, the excessive
lymphocytes can begin to attack the body’s own
normal cells.
• apoptosis also directly fights infection as part of the
immune system’s first line of defense against foreign
invaders such as bacteria, viruses, or fungi. As part
of the first response to infection, apoptosis is
activated in cells infected by the invader, leading to
their destruction.
Apoptosis in development
Nat Rev Mol Cell Biol. 2006 Feb;7(2):97-108.
Developmental apoptosis in C. elegans: a complex CEDnario.
Lettre G, Hengartner MO.
Source
Division of Genetics, Children's Hospital, 300 Longwood Avenue,
Boston, Massachusetts 02115, USA.
Abstract
Apoptosis, an evolutionarily conserved programme of cellular selfdestruction, is essential for the development and survival of most
multicellular animals. It is required to ensure functional organ
architecture and to maintain tissue homeostasis. During
development of the simple nematode Caenorhabditis elegans,
apoptosis claims over 10% of the somatic cells that are generated these cells were healthy but unnecessary. Exciting insights into the
regulation and execution of apoptosis in C. elegans have recently
been made. These new findings will undoubtedly influence our
perception of developmental apoptosis in more complex species,
including humans.
Apoptosis & Flower Development
• The duration of the flower is species-specific and
carefully tailored to its ecological requirements. This is
important because firstly the flower can be a
substantial sink on the plant’s resources, and as such
is energetically expensive to maintain beyond its
useful life.
• In addition, its architecture has been exploited by
pathogens that use the stigma as a point of entry, and
thus the flower poses an added risk of pathogen
attack.
• Another important reason for floral death after
pollination is to remove it from the population so that
it does not compete for pollinators with the remaining
blooms.
Essential knowledge 2.E.2:
Timing and coordination of
physiological events are
regulated by multiple
mechanisms.
In plants, physiological events involve
interactions between environmental
stimuli and internal molecular signals.
2 examples:
• Phototropism, or the response to the presence of
light
• Photoperiodism, or the response to change in
length of the night, that results in flowering in
long-day and short-day plants
Tropisms- plant response to
environmental stimuli
• Phototropism
• Gravitropism
• Thigmotropism
Plant hormones, such as auxin, are
responsible for plant movement
• ✘✘Memorization of the names, molecular structures and specific
effects of all plant hormones are beyond the scope of the course and
the AP Exam.
Photoperiodism
In fungi, protists and bacteria, internal and
external signals regulate a variety of
physiological responses that synchronize with
environmental cycles and cues.
• Two illustrative examples of this are:
• Fruiting Body Formation in Fungus
• Quorum Sensing in Bacteria
Fruiting body formation in fungi, slime
molds and certain types of bacteria
• Fruiting bodies are spore producing structures
• Fruiting body formation is influenced by
external factors such as season (which affects
temperature and air humidity)
Quorum sensing in bacteria
• Quorum sensing is a system of stimulus and
response correlated to population density.
• Used to coordinate gene expression according to
the density of their local population.
• Bacteria use it to coordinate certain behaviors
based on the local density of the bacterial
population.
• http://www.ted.com/talks/bonnie_bassler_on_
how_bacteria_communicate.html