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Control of Development
Topic 3.3
Topic 3 specification
• 13 Explain how cells become specialised
through differential gene expression,
producing active mRNA leading to synthesis of
proteins, which in turn control cell processes
or determine cell structure in animals and
plants (details of transcription factors are not
required at IAS).
• 5 Describe how the cells of multicellular
organisms can be organised into tissues,
tissues into organs and organs into systems.
Acetabularia experiments
• Read pages 125-126
• Acetabularia is a type of green algae. It is single cellular
but giant in size compared to other types of algae, 0.5 to
10 cm in height.
• Read Activity 3.13• Why is this organism chosen for this experiment?
• What is done in each experiment?
What conclusions can you draw?
What is the function of genetic material/DNA?
Where could the genetic material be? Rhizoid? Tip? Stem? Explain
To what extent does this experiment support or
contradict the conclusion from experiment 1?
Remember- where could the genetic material be according to
Experiment 1?
Does experiment 2 support these conclusions? All of them? Some of
them?
Suggest what could be happening to the genetic material in experiment
2.
What extra information does the result of Experiment 3
give you that supports or modifies your answer to 1?
What conclusions can be reached about the role of the
nucleus?
What can you conclude from experiment 4 about what
influences development of the tip of the Acetabularia cell?
• In step 3 which
features were in each
hat? Suggest an
explanation.
• In step 4 which
features were in each
hat? Suggest an
explanation.
• Hint: think of the role,
location and
permanence in cell of– DNA
– RNA
Cloning
• Read pages 126-127
• Using figure 3.36, label
the same figure in your
handout packet.
– Egg donor
– Mammary cell (diploid
cell) donor
– Haploid nucleus
– Diploid nucleus
– Surrogate mother
– Early embryo
• How did the creation of Dolly support the idea
that all the genetic information for making a
complete organism is present in any
specialized cell?
– nucleus (diploid)
– Specialized mammary cell
– Nucleus (haploid)
– Ovum
– What was the result?
Therapeutic cloning (from 3.2)
• Read page 122-123. Outline the steps in therapeutic
cloning.
– diploid nucleus
– somatic cell (body cell)
– ovum
– haploid nucleus
– Mitosis
– blastocyst stage (about 5 days)
– Stem cell- encouraged to develop into tissues/organs
for transplant.
• How does therapeutic cloning and the cloning described
in fig 3.36 differ?
• What problems have come up with cloned animals?
Gene Expression- Introduction
• What happens to a zygote after fertilisation?
– Mitosis
– Differentiation: Process of specialisation of cells
• Are all the cells genetically different? Explain.
– All cells produced by mitosis contain the same DNA.
• How is this ensured in mitosis (covered in 3.2)?
– S phase, DNA replication
– Metaphase, chromosomes lining up at the equator
– Anaphase, chromatids being pulled to either end of
the cell
Pictures and Animations
• http://www.youtube.com/watch?v=qisrNX3Qj
Ug - gastrulation and neurulation (sped up)
• http://embryo.soad.umich.edu/carnStages/ca
rnStages.html - pictures of several stages of
embryo development
• http://www.youtube.com/watch?v=_Nl68Nc_
Dlc - gastrulation and neurulation (more
detail, longer)
Differential Gene Expression
• Read pages 128-129
• What is meant by the term differentiate:
– When cells develop a special __________due to developing a special
___________
• How does differentiation happen?
– Only _________ genes are being switched ____(expressed) or
permanently switched ____ (not expressed). (Imagine that genes can
be on standby). This is triggered by specific chemical _______.
• What is the result of a gene being switched on?
– Active _____ is produced by __________ from switched on genes
–  _________ is produced by __________ of active mRNA
–  Proteins may be ________ catalyzing specific cell reactions,
transport proteins in the cell ___________, or specific ________
proteins affecting the shape of the cell. Both determine cell
f__________.
• Label the diagram using colours
if necessary
• mRNA
• Differentiated cells
• Undifferentiated cells
• cDNA
• What is cDNA?
• https://www.dnalc.org/view/16736Animation-36-Different-genes-areactive-in-different-kinds-of-cells.html - not all of it is relevant
• Explain in your own words the
conclusion of this experiment.
Switching Genes On
• Read pages 128-129
• What is lactose?
– disaccharide found in milk, composed of glucose and galactose
• Which enzyme catalyzes the breakdown of lactose?
– beta galactosidase
• Where and under which condition(s) is this enzyme naturally produced?
– E. _______ produce this enzyme but only when _______ is present
(specific ________ stimulus).
• What happens if the b-galactosidase gene is activated(switched on)
–  _______ is produced by _____________
–  _______ is produced by _____________
–  cell can carry out its particular function due to the production of
beta galactosidase
In Prokaryotes- Figure 3.38
• What has to bind
to part of the DNA
before
transcription can
occur? Where
exactly on the DNA
does the molecule
named above
bind?
• What does the
repressor molecule
do if lactose is
absent?
• What happens if
lactose is present?
• How is this method of switching on genes advantageous
to E. Coli?
B-galactosidase gene
Label the followingGene for B-galactosidase
RNA polymerase
Repressor molecule
Lactose
Point where transcription begins
Point where transcription ends
In Eukoryotes- Figure 3.39
• Read pages 139
• What is the promoter region?
– Where the RNA polymerase
binds
• What does a regulator protein do?
– Also binds to promoter region
so that RNA polymerase can
bind and transcription can start
• What can a protein repressor
molecule do?
– Can bind to either the
promoter region or the
regulator protein and prevent
RNA polymerase from binding
and so prevent transcription.
Gene expression, some examples
• The gene expressed is determined by external
or internal stimuli.
• Prokaryotes, external: lactose (chemical
stimulus)
• Eukaryotes, external: chemicals secreted by
neighbouring cells. Highest concentration
from nearby cells so location determines how
it differentiates.
Eukaryotes, internal stimuli
• After fertilisation the zygote contains only one
nucleus with all of the genetic information.
• Chemicals in the cytoplasm are not equally
distributed.
• After mitosis the cells are genetically identical
but the cytoplasms are not identical.
• Some chemicals are regulator or repressor
proteins turning genes on/off.
Gene expression Quiz
1. What is cDNA? How is it
produced?
2. How did Dawid and
Sargent’s experiment
show that differentiated
and undifferentiated
cells express some of
the same genes but
also some different
genes.
Gene expression Quiz
3. Which molecule has to bind with the operator gene before
transcription can occur?
4. Under what condition(s) does E.coli NOT produce B-galactosidase?
Why not?
5. Under what condition(s) does E. Coli produce B-galactosidase?
Why?
6. What is the role of a regulator protein?
7. Suggest what could prevent the regulator protein from binding?
8. Switching a gene on is triggered by a stimulus. Give an example of
such a stimulus is aa. Prokaryotic organism
b. Eukaryotic organism
9. Outline the steps explaining how an embryonic cell might develop
into a specialised red blood cell.
FOP
• Fibrodysplasia ossificans progressiva
• Symptoms
• Inherited disease where bone grows when tissue gets
damaged.
• Cause?
•
•
•
•
•
•
(Draw to illustrate)
Chemical stimulus (protein)
White blood cells
Muscle cells
Stimulate
Differentiation into bone cells.
• Can it be treated?
• No
Organisation within organisms
•
•
•
•
•
Cells 



Cells  Tissues  Organs  Organ Systems  Organism
Compare: Tissue, organ and organ system.
Q 3.16
How do cells stick to other cells in the same tissue?
• Adhesion molecules on cell surface membranes hold cells together in
tissues.
• In your notebook sketch a cell membrane and include the following:
–
–
–
–
–
–
–
Phospholipid bilayer
Hydrophilic phosphate heads
Hydrophobic tails
Membrane proteins
Glycoproteins
Glycolipids
Cholesterol
Cell Membrane
• Label a possible recognition/adhesion molecule.
– Must project out
• These recognition molecules can be
_____________________ which have a specific
_____________. Cells with recognition proteins with the
complementary __________ can stick together.
• Recognition molecules also interact with the extracellular matrix (outside of the cell)
• During development of embryo the type of molecule
found on cells’ surface can ________- therefore the
________ changes, this allows tissues to be re-organised
during development.
Switching on (Activating) a chromosome
Gender Determination
• Female: XX , Male: XY
• So what exactly decides male/female
characteristics in Humans? Are the male
characteristics on the Y chromosome and the
female ones on the X?
– In development default is female
– Y chromosome codes for proteins which turn on genes for male characteristics
– Remember males also have an X chromosome- there is nothing female about it.
• Tom cat: male cat
• Extension 3.5
Master Genes
• Read pages 132-133 on your own
• What are master genes? How do they work?
– Control the basic body plan by– Controlling the development of sections of an
organism by coding for signal proteins.
– Signal proteins switch on the necessary genes.
Flowering Plants
• Label on Activity 3.15
• Review functions:
–
–
–
–
–
–
–
–
–
Stamen
Anther
Filament
Carpel
Stigma
Style
Ovary
Sepal
Petals
Identify the four whorls.
Master Genes in Flowers
• Meristem– tissue in plants made up of undifferentiated cells.
– Which processes do you think happen here/start
here?
• Mitosis
• Differentiation starts here
• Read Activity 3.15 Modelling Flowers
• Wild type: plants with NO mutation
• Mutant master genes: What is the result?
– do not result in functioning signal proteins
• Q 1,5
Figure 3.44, page 133
Show how diagram on right
illustrates conclusions from the
experiment.
Apoptosis
• Programmed cell death
• Read ‘Did you know?’ on page 133
Activity 3.15b How Cells become specialised
• As cells become more differentiated , their structure becomes
specialised; they have a restricted range of functions , or just
one particular function . The proteins synthesised by the cell
determines its structure and function. For instance, a ciliated
lung epithelium cell produces the proteins to make the cilia. A
white blood cell which produces antibodies as part of the
immune response will be able to make these protein
antibodies. The genes for the particular proteins required for
the specialised structure and function will only be translated
and transcribed in particular specialised cells. If the gene is
transcribed, mRNA is produced. This is then translated on
the ribosomes and the protein is produced. The proteins may
be produced all the time if they are structural components of
the cell or required continually for the functioning of the cell.
Some proteins may only be produced periodically when
required.
Topic 3 specification
• 13 Explain how cells become specialised
through differential gene expression,
producing active mRNA leading to synthesis of
proteins, which in turn control cell processes
or determine cell structure in animals and
plants (details of transcription factors are not
required at IAS).
• 5 Describe how the cells of multicellular
organisms can be organised into tissues,
tissues into organs and organs into systems.