Dev bio first lecture ppt 1
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Transcript of Dev bio first lecture ppt 1
Basic attributes common to many forms of life
Cellular structure and intracellular compartmentalization; and
Metabolism and transfer of energyStorage and transmission of genetic informationReproduction
Development- each individual will go through certain changes of form and function during its life
A After a corn grain (seed) germinates, its radicle and coleoptile emerge. The radicle develops into the primary root. The coleoptile grows upward and opens a channel through the soil to the surface,
B The plumule develops into the seedling’s primary shoot, which pushes through the coleoptile and begins photosynthesis. In corn plants, adventitious roots that develop from the stem afford additional support for the rapidly growing plant.
Fig. 31-3, p. 525
Stepped Art
hypocotyl
radicle
branch root
branch root
primary root
primary root
adventitious (prop) root
primary leaf
coleoptile
coleoptile
coleoptile
Early Growth of a Bean (Eudicot)
Fig. 31-4a, p. 525
seed coat radicle
cotyledons (two)
hypocotyl
primary root
A After a bean seed germinates, its radicle emerges and bends in the shape of a hook. Sunlight causes the hypocotyl to straighten, which pulls the cotyledons up through the soil.
Fig. 31-4b, p. 525
primary leaf
primary leaf
withered cotyledon
branch rootprimary root
root nodule
B Photosynthetic cells in the cotyledons make food for several days, then the seedling’s leaves take over the task. The cotyledons wither and fall off.
Fig. 31-22, p. 535
germinationmature
sporophyte (2n)
zygote in seed (2n)
fertilizationmeiosis in anther
meiosis in ovary
DIPLOID
HAPLOID
microspores (n)
megaspores (n)
eggs (n) sperm (n)
male gametophyte (n)
female gametophyte (n)
Plant Development
• Plant development includes seed germination and all events of the life cycle, such as root and shoot development, flowering, fruit formation, and dormancy
• These activities have a genetic basis, but are also influenced by environmental factors
Pollination and fertilization
Development- process – complex, multicellular organism arises from a single cell, a gradual process, so the complexity of the embryo increases progressively.
Development –progressive-i.e. a simple embryo with few cell types organized in a crude pattern gradually refined to generate a complex organism with many cell types showing highly detailed organization.
Development- process by which an organism changes to acquire new structures and abilities. It occurs in response to various levels of control:
1. Genetic instructions2. Intercellular interaction3. Environmental factors
gametes
zygote
Differentiation Pattern formation
MorphogenesisCell division
Growth
Diversificationof cell types
OrganizationGenerationof shapes & structures
Increase incell number
Increase
in size
Adult
Gametes
Major overlapping processes
Growth : increase of size and weight,.Diameter, height, volume and weight can be measured. Biochemical properties can also be established:
Enzyme activity, pigment content, protein content, DNA and RNA content may be used to characterize the organism.
Single cells show 2 major components of growth: division and enlargement
After imbibition of water by seeds, the growth by whichthe embryo becomes a young seedling occurs by bothexpansion of cells originally present in the dormant embryoand mitotic divisions resulting in an increase in cell number
gametes
zygote
Differentiation Pattern formation
MorphogenesisCell division
Growth
Diversificationof cell types
OrganizationGenerationof shapes & structures
Increase incell number
Increase
in size
Adult
Gametes
Major overlapping processes
Cell division
The plane in which a cell divides is determined during late interphase.
First sign of this spatial orientation is rearrangement of the cytoskeleton In the cytoplasm into a ring called pre-prophase band. Band disappears before metaphase but it predicts the future plane of division. It predicts where the cell plate will be inserted (the division site).
The “imprint” consist of actinmicrofilaments that remainafter microtubules disperse.
Fig. 35-25
Plane ofcell division
(a) Planes of cell division
Developingguard cells
Guard cell“mother cell”
Unspecializedepidermal cell
(b) Asymmetrical cell division
If planes of division of the descendants are parallel to the plane of the ist cell division, single file of cells results.
Cell division in 3 planes gives rise to a cube. If planes vary randomly, will be a disorganized clump.
Guard cells form perpendicular to the first division
PLANES OF DIVISION VARY AS DEVELOPMENT OF CALLUS
Cell expansion contributes to plant form.Orientation of cell growth is in the plane perpendicular to the orientation of the cellulose microfibrils in the wall. Enzymes weaken cross-links in the wall, and allow it to expand as water diffuses into vacuole by osmosis.
The orientation of cellulose microfibrils (CMFs) is a determining factor in cell growth. Elongation is favored when CMFs are oriented transversely to the direction of growth while elongationis limited when CMFs are oriented in the oblique or longitudinal direction.
Orientation of cellulose microfibrils in growth- cell expansion. CA 80 CELLULOSE IN A MICROFIBRIL
Auxins in cell expansionENZYME THAT BREAKS CROSS LINKSOR HYDROGEN BONDS BETWEENCELLULOSE MICROFIBRILS
gametes
zygote
Differentiation Pattern formation
MorphogenesisCell division
Growth
Diversificationof cell types
OrganizationGenerationof shapes & structures
Increase incell number
Increase
in size
Adult
Gametes
Major overlapping processes
Cell DifferentiationCells become specialized in structure and function. A fertilized egg gives rise to many different kinds of cells, each with a different structure and function.
A program of differential gene expression (the expression of different sets of genes by cells with the same genome) leads to the different cell types in a multicellular organism
Gene expression Cells must continually turn genes on and off in response to signals from external and internal environment.
Regulation of gene expression is necessary for cell specialization in multicellular organisms.
The differences between cell types are not due to different genes being present but to differential gene expression, the expression of different sets of genes by cells with the same genome
DNA
Primary RNA transcript
proteininactive mRNA
Inactive protein
mRNA degradation control
Translational control by ribosome selection among mRNAs
Protein activity control
Transcriptional control
1
2 Processing control
3 Transport control
mRNA
mRNA
6
4 5
Steps at which gene expression can be controlled in eukaryotes
NUCLEUS
CYTOPLASM
Each stage is a potential control point at which gene expression can be turned on or off, accelerated or slowed down.
In all organisms, a common control point for gene expression is at transcription
. In this stage regulation is often in response to signals coming from outside cell e.g. hormones or other signaling molecules.
gametes
zygote
Differentiation Pattern formation
MorphogenesisCell division
Growth
Diversificationof cell types
OrganizationGenerationof shapes & structures
Increase incell number
Increase
in size
Adult
Gametes
Major overlapping processes
Pattern structure
Form –one of outstanding characteristics of living organisms.
Though complex,various parts bear predictable, repeated relations to one another.
Regularity or deviation from random distribution of various parts of cells or tissues
O X O
O X O
O X O
The distribution of the specialized cell is not random since the location of any given cell is at least predictable from the location of other cells
B
X O
X O
X O
X O
X X
X X O O
X x O O
O O
C
D
Non-random
Non-random
Non-random
O X O
X
X O
O X
O X O
O X O
O X O
A
B
X O
X O
X O
X O
X X
X X O O
X x O O
O O
C
D
random
Non-random
Non-random
Non-random
Pattern formation- Development of a spatial organization in which the tissues and
organs are all in their characteristic places.
It is the development of specific structures in specific locations. Cells must be organized into multicellular arrangements of tissue and organs.
Pattern formation is determined by positional information in the form of signals that continuously indicate to each cell its location within a developing structure
Each cell within a developing organ responds to positional information from neighbouring cells by differentiating into a particular cell type, oriented in a particular way.- gradients of specific molecules- hormones, proteins -mRNA provide positional information
Pattern formation
First patterning event in the embryo- axis specification. This reflects asymmetric division of the zygote:
apical cellbasal cell
Establishment of the principal body axis--ANTEROPOSTERIOR--DORSOVENTRAL
embryo
Suspensor filament
Arrangement of leaves
Leaf primordia flanking the apical meristem
Development of zygote into an embryo
Organ expansion and maturationGlobular-heart transition
Embryogenesis
X-section of a young root Epidermal tissue
Morphogenesis- creation of form
Physical process that give an organism its shape in each cell type
The different kinds of cells not randomly distributed but organized into tissues and organs in a particular three- dimensional arrangement.
Reflects different aspects of cell structure and behavior including: cell division, cell shape and size, interaction between cells , and cell death.
In animals, morphogenesis – many involve movement of cells relative to other cells
In plants, cells have cell walls and middle lamella which tightly cement cells together. No relative cell movement or migration. Morphogenesis reflects a restricted set of processes-such as:
1.differential rates and planes of cell division
2. changes in cell size due to the increasing volume of the vacuole.
Planes of cell division determine shape of particular tissues.
Terms to describe planes of cell division:anticlinal – SURFACE GROWTH.
occur in the plane of the sheet- expands the sheet WITHOUT INCREASING THE THICKNESS.
periclinal- occur at right angles to the plane of a sheet so results in its expansion into multiple layers.
Switching from anticlinal to periclinal cell division is critical for some morphogenetic processes, e.g. outgrowth of leaves.
Model organismsUses:• to gain comprehensive knowledge about a complete plant. • to further detailed understanding of mechanisms and processes in plants.• to understand particular biological phenomena with the expectation that discoveries made on the model organism will provide insight into the workings of other organisms Select model organism that lend themselves to study of a particular group and are representative of a larger group.
Arabidopsis thaliana
Small, ca 30 cm tall, with flat rossette of leaves.
Arabidopsis thaliana (wall cress)Small, less than 30 cmLife cycle-about 6-8 weeks, hermaphrodite flowers, self-fertilizing flowers.
Easy to grow large numbers in the lab. Under continuous light 25 degrees centigrade, up to 10,000 to 50,000 seeds. Plants can grow to form ripe seeds within 8 weeks
A single flower can produce 30-50 seeds. Whole plant can produce several thousands, up to 10,000 seeds per plant making study of genetics easier.
Ideal for isolating mutants and for genetic characterization of mutants
2n=10, have 26,700 protein-encoding genes but many are duplicates, ca 15,000 different types of genes,
It has one of the smallest genomes in the plant kingdom: 115,409,949 base pairs of DNA distributed in 5 chromosomes (2n
= 10).
Very little "junk" DNA
Transgenic plants can be made easily using Agrobacterium tumefaciens as the vector to introduce foreign genes.
Mutations can be easily generated (e.g., by irradiating the seeds or treating them with mutagenic chemicals).
It is normally self-pollinated so recessive mutations quickly become homozygous and is expressed
Aim is to to establish a blueprint for how plants develop
inflorescences
• 2n=20, 10 large chromosome pairs•Large no of progeny per cross ca 100 to 200 )•Facilitated discovery of transposons (jumping genes)-mobile genetic elements that disrupt the functions of some genes.
Levels of developmental control
1. Genetic and intracellular control of development. An individual mature cell in the vegetative body of the plant retains within nucleus all the genetic information to reproduce the dev. steps necessary to form the whole organism.Genetic constitution is expressed in terms of the biochemical events within the cell which lead to specific cell differentiation at specific times.
Transplantation experiments inAcetabularia mediterranea and A. crenulata
Shows importance of nucleusfor cell differentiation
Morphogenesis of the cap is dependent upon species-specific RNA molecules translated into proteins
Flow of genetic information
Fig. 14-4, p. 218
Stepped Art
DNA template
New DNA strand
DNA template
RNA transcript
Transcription
Genetic Information• From DNA to mRNA to amino acid
sequence
Levels of developmental control
2. Hormonal and intercellular control of developmentA hormone may act by altering gene expression affect activity of existing enzymes
changing properties of membrane
Any of the above could redirect the metabolism and development of a cell responding to small number of molecules
Lack abscissic acid
MAIN Factor that affects color is soil pH. Acidic= pink/red flowersAlkaline= blue flowers
Environmental factors
Etiolated shoot in potato –developing in the absence of light, turn green upon exposure to light. The plant is able to detect the light intensity and wavelength by using photoreceptors , but receptordoes not interact directly with the cell’s DNA but a signal transduction chain is involved:phytochrome, blue light/UV-A and UV-B receptors .