1. Cellular Control F215 control genomes and environment
Module 1 Cellular Control and Meiosis

2. Learning outcomes
state that genes code for polypeptides, including enzymes;
explain the meaning of the term genetic code;
describe, with the aid of diagrams, the way in which a nucleotide sequence codes for the amino acid sequence in a polypeptide;

3. Learning Outcomes
describe, with the aid of diagrams, how the sequence of nucleotides within a gene is used to construct a polypeptide, including the roles of messenger RNA, transfer RNA and ribosomes;

4. Learning Outcomes
state that mutations cause changes to the sequence of nucleotides in DNA molecules;

5. Mutations Definitions Mutation Mutant Mutagen
A change in gene or chromosome structure
Mutant
An individual showing or carrying a mutation
Mutagen
A chemical or physical agents causing a mutation

6. Mutations There are two types of mutation Gene mutation
Affects a single gene
A chromosome mutation
Affects a single chromosome or set of chromosomes

7. Gene Mutations - Mutant alleles
Occur at random
Are spontaneous
Are rare
Can be increased by chemicals or radiation

8. CCT AGT ATT CGC TGA GGC TAA TG
Gene Mutation
This results from a change in base sequence of the DNA of a gene
This means a different protein is coded for
Look at the sequence of bases below:
CCT AGT ATT CGC TGA GGC TAA TG

9. CCT AGT ATT CGC TGA GGC TAA TG
Now look at the three sequences below
Describe the change you see in each sequence
CCT AGA ATT CGC TGA GGC TAA TG
CCT AGT TTC GCT GAG GCT AAT G
CCT AGT AGT TCG CTG AGG CTA ATG

10. Gene mutations
Use one of the three terms below to describe each sequence
Substitution
Deletion
insertion

11. Gene Mutations Substitutions will only alter one codons
This results in only one amino acid in the protein being changed
This is known as a point mutation
Insertions and deletions cause a shift in the whole sequence of bases and all the codons after that point are altered.
This is a frame shift.

12. Gene Mutations

13. Frame Shift

14. Learning Outcomes
explain how mutations can have beneficial, neutral or harmful effects on the way a protein functions

15. Effects of gene mutations
Give suggestions for each of the three effects of mutations below:
Beneficial
Neutral
Harmful

16. Beneficial Mutations
These are mutation which offer a selective advantage to an individual.
Well-adapted organisms can out-compete those in the population without the advantageous characteristic
This is the driving force behind natural selection

17. Neutral Mutations If the mutation occurs in the non-coding part of DNA
Silent mutation
Base triplet is changed but has no effect on the amino acid coded for.

18. Harmful Mutations
70% of cystic fibrosis sufferers, the mutation is a deletion of a triplet of base pairs
Protooncogenes can be changed into oncogenes by a point mutation, which promote uncontrolled cell division
Huntington disease is caused by a stutter – this is repeating sections of CAG sequences,

19. Sickle Cell Anaemia Haemoglobin Globular protein
Two α polypeptide chains
Two β polypeptide chains
A mutation in the gene coding for the β chain causes sickle cell anaemia

20. Sickle Cell Anaemia

21. Sickle Cell Anaemia
When the four polypeptide chains curl up they form a specific 3-D shape
Some amino acids have hydrophobic side chains e.g. valine
Some amino acids have hydrophillic side chains e.g. glutamate
If the O2 level in blood falls, valines form bonds with themselves that stick haemoglobin molecules together, producing long chains of stuck-together haemoglobin molecules, the RBC is pulled out of its usual biconcave shape.

22. Harmful or Beneficial Mutations
If a mutation changes a characteristic, there can be an advantage or a disadvantage to having this new character.
the environment plays a role in determining the likelihood of this characteristic being maintained through natural selection.

23. Skin colour and Vitamin D synthesis
Background:
Melanin is a skin pigment that protects cells from the harmful effects of UV radiation.
Vitamin D is synthesised when skin is exposed to sunlight.

24. Early humans had dark skin
Light skin does not shield against harmful UV- causes skin cancer.
Vitamin D can be synthesised
Dark skin protects from harmful UV rays.
Sunlight is intense enough to synthesis vit.D.

25. Migration to temperate climes
Dark skin not needed to protect against UV.
Melanin prevents sunlight synthesising vitamin D.
Sunlight less intense- lowered intensity of UV (no skin cancer)
Vitamin D can be synthesised

26. Inuit People
The Inuit people still retain some skin pigments, but do not live in an environment with high levels of UV/sunlight.
Is melanin a disadvantage?
Diet is high in Vitamin D, so no need to reduce melanin levels in order to synthesise vitamin D.

27. Learning Outcomes
state that cyclic AMP activates proteins by altering their three-dimensional structure;

28. Learning outcomes
explain genetic control of protein production in a prokaryote using the lac operon

29. The Lac operon
E. coli is capable of synthesising a variety of different enzymes, depending on their environment.
E. coli only produce enzymes needed to metabolise lactose when lactose is present in the substrate
ß-galactosidase:
catalyses hydrolysis of lactose.
Lactose permease:
transports lactose into the cell.

30. The operon consists of several genes
Regulatory gene
for lac operon
Control sites
Structural genes
P: Promoter region. RNA polymerase binds here to start
transcription of Z & Y.
O: Operator region. Switches Z & Y on and off.
Z: Codes for ß-galactosidase.
Y: Codes for lactose permease.

31. What Happens Without Lactose?
mRNA
ribosome
repressor protein
Regulator gene is expressed and produces REPRESSOR PROTEIN.
One binding site on Repressor protein binds to operator region, covering promoter region where RNA polymerase would attach.
RNA polymerase cannot bind to promoter region and neither gene Z or Y is expressed.

32. What Happens With Lactose?
ß-galactosidase
Lactose permease
lactose
Lactose binds to other binding site on repressor protein, changing the shape.
Repressor protein cannot bind to operator region
RNA polymerase binds to promoter region and genes Z & Y are expressed.

33. Learning Outcomes
explain that the genes that control development of body plans are similar in plants, animals and fungi, with reference to homeobox sequences (HSW1);

34. Homeobox genes
Homeobox genes determine how an organism’s body develops as it grows from a zygote into a complete organism.
They determine the organism’s body plan
These sequences are highly conserved, which implies that their activity is fundamental to the development of an organism
Homeobox genes have been discovered in animals, plants and fungi

35. Homologous homeobox genes
These are the sequences of 60 amino acids in the proteins coded for by the homeobox genes Antp in a fruit fly and HoxB7 in a mouse.
All animals have homologous homeobox genes – they are recognisably similar

36. Genes and Body plans Drosophila melanogaster a.k.a. fruit fly
Body is divided into
Head
Thorax
abdomen

37. Genetic control of Drosophila development
Development is mediated by homeobox genes
Maternal effect genes determine the embryo’s polarity e.g. anterior (head) & posterior (tail / abdomen)
Segmentation genes determine polarity of each segment
Homeotic selector genes identify and direct the development of each segment
Two groups exist, that control development of (i) head + thorax segments and (ii) thorax + abdomen segments.

38. Drosophila thorax The Thorax of the fruit fly is split into 3 segments
T1 – a pair of legs
T2 – a pair of legs and a pair of wings
T3 – a pair of legs and a pair of halteres

39. Ubx in fruit fly
A homeobox gene called Ubx stops the formation of wings in T3.
A mutation in both copies of Ubx, wings grow in T3 instead of halteres.
Ubx
Mutant
Ubx

40. Antp in fruit fly
If the homeobox gene Antp is usually turned on in the thorax, where it causes legs to develop.
In mutant flies where Antp is switched on in the head, legs grow instead of antennae

41. What do homeobox genes do?
Homeobox genes code for the production of transcription factors
These proteins can bind to a particular region of DNA and cause it to be transcribed
A single homeobox gene can switch on a whole collection of other genes, regulating gene expression

42. Hox Clusters
Hox clusters are aggregations of homeobox genes and are found in all animals.
Examples
Nematodes have one Hox cluster
Fruit flies have 2 Hox clusters
Vertebrates have 4 Hox clusters

43. Homeobox genes in humans
Effect of thalidomide in embryo development
Homeobox genes HoxA11 and HoxD11 switch on genes that cause forelimb development.
The drug thalidomide affected the behaviour of these homeobox genes at a critical stage in embryonic development.

44. Homeobox genes in humans
Retinoic acid and birth defects
Retinoic acid
is a derivative of vitamin A
activates homeobox genes in vertebrates
Is a morphogen (substance governing pattern of tissue development).
If a pregnant woman takes too much Vitamin A, it can interfere with the expression of these genes causing birth defects in the central nervous system and axial skeleton

45. Homeobox animation http://www.dnaftb.org/dnaftb/37/concept/index.html
If you have time, sit and watch this animation, as well as investigating other aspects of this web site.

46. Learning outcomes
outline how apoptosis (programmed cell death) can act as a mechanism to change body plans

47. Apoptosis Apoptosis is programmed cell death in development
Series of biochemical events leading to an orderly and tidy cell death
Hayflick Constant
Cells undergo about 50 mitotic divisions before apoptosis
Necrosis
Untidy and damaging cell death occurring after trauma

48. Sequence of Apoptosis Enzymes breakdown cell cytoplasm
Cytoplasm becomes dense
Organelles are tightly packed
Cell surface membrane changes and blebs form
Chromatin condenses, nuclear envelope breaks
Cell breaks into vesicles
phagocytosis

49. Apoptosis

50. Apoptosis

51. Control of Apoptosis Apoptosis is controlled by cell signalling
Cytokines from the immune system
Hormones and growth factors
Nitric oxide
Makes inner mitochondrial membrane more permeable to hydrogen ions

52. Apoptosis and tissue development
The rate of cells dying should balance the rate of cells produced by mitosis
Not enough apoptosis leads to the formation of tumours
Too much leads to cell loss and degeneration
Cell signalling plays a role in maintaining the correct balance

53. Apoptosis in Development
The formation of the digits (fingers and toes) occurs due to apoptosis during the development of the embryo.

54. Apoptosis and metamorphosis
As tadpoles grow they develop legs, change their body shape and lose their tails
The tail is lost by apoptosis