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Cellular Control. F215 control genomes and environment Module 1 Cellular Control and Meiosis. Learning outcomes. state that genes code for polypeptides, including enzymes; explain the meaning of the term genetic code ;

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Cellular Control

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Cellular Control

F215 control genomes and environment

Module 1 Cellular Control and Meiosis

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;

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;

Learning Outcomes

  • state that mutations cause changes to the sequence of nucleotides in DNA molecules;


  • Definitions

    • Mutation

      • A change in gene or chromosome structure

    • Mutant

      • An individual showing or carrying a mutation

    • Mutagen

      • A chemical or physical agents causing a mutation


  • There are two types of mutation

    • Gene mutation

      • Affects a single gene

    • A chromosome mutation

      • Affects a single chromosome or set of chromosomes

Gene Mutations - Mutant alleles

  • Occur at random

  • Are spontaneous

  • Are rare

  • Can be increased by chemicals or radiation

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:



  • Now look at the three sequences below

  • Describe the change you see in each sequence




Gene mutations

  • Use one of the three terms below to describe each sequence

    • Substitution

    • Deletion

    • insertion

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.

Gene Mutations

Frame Shift

Learning Outcomes

  • explain how mutations can have beneficial, neutral or harmful effects on the way a protein functions

Effects of gene mutations

  • Give suggestions for each of the three effects of mutations below:

    • Beneficial

    • Neutral

    • Harmful

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

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.

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,

Sickle Cell Anaemia

  • Haemoglobin

    • Globular protein

      • Two α polypeptide chains

      • Two β polypeptide chains

    • A mutation in the gene coding for the βchain causes sickle cell anaemia

Sickle Cell Anaemia

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.

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.

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.

Dark skin protects from harmful UV rays.

Sunlight is intense enough to synthesis vit.D.

Light skin does not shield against harmful UV- causes skin cancer.

Vitamin D can be synthesised

Early humans had dark skin

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

Migration to temperate climes

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.

Learning Outcomes

  • state that cyclic AMP activates proteins by altering their three-dimensional structure;

Learning outcomes

  • explain genetic control of protein production in a prokaryote using the lac operon

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.

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.

What Happens Without Lactose?



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.

What Happens With Lactose?


Lactose permease


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.

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);

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

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

Genes and Body plans

  • Drosophila melanogaster a.k.a. fruit fly

  • Body is divided into

    • Head

    • Thorax

    • abdomen

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.

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

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.




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

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

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

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.

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

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.

Learning outcomes

  • outline how apoptosis (programmed cell death) can act as a mechanism to change body plans


  • 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

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



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

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

Apoptosis in Development

  • The formation of the digits (fingers and toes) occurs due to apoptosis during the development of the embryo.

Apoptosis and metamorphosis

  • As tadpoles grow they develop legs, change their body shape and lose their tails

  • The tail is lost by apoptosis

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