Differences between prokaryotes & eukaryotes. Gene function

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1 GENE REGULATION

2 Differences between prokaryotes & eukaryotes Gene function

3 Description of Prokaryotic Chromosome and E.coli Review

4 Differences between Prokaryotic & Eukaryotic Chromosomes Four differences

5 Eukaryotic Chromosomes Form Length in single human chromosome Length in single diploid cell Proteins beside histones Proportion of DNA that codes for protein in prokaryotes eukaryotes humans

6 Regulation of Gene Expression in Prokaryotes Terms promoter structural gene operator operon regulator repressor corepressor inducer

7 The lac operon - Background E.coli behavior presence of lactose and absence of lactose behavior of mutants outcome of mutants

8 The Lac operon Regulates production of b-galactosidase

9 The trp operon Regulates the production of the enzyme for tryptophan synthesis

10 General Summary During transcription, RNA remains briefly bound to the DNA template Structural genes coding for polypeptides with related functions often occur in sequence Two kinds of regulatory control positive & negative

11 General Summary Regulatory efficiency is increased because mrna is translated into protein immediately and broken down rapidly. 75 different operons comprising 260 structural genes in E.coli

12 Gene Regulation in Eukaryotes some regulation occurs because as little as one % of DNA is expressed

13 Gene Expression and Differentiation Characteristic proteins are produced at different stages of differentiation producing cells with their own characteristic structure and function. Therefore not all genes are expressed at the same time As differentiation proceeds, some genes are permanently turned off. Example - different types of hemoglobin are produced during development and in adults. DNA is expressed at a precise time and sequence in time.

14 Gene Expression and Differentiation DNA segments only produced at a certain time Differentiation in multicellular organisms depends on inactivation of certain genes and activation of others.

15 Methods of Regulation: relating to only part of the genome is expressed Selective control of genes is needed for differentiation - how? Condensation: folding of chromatin to create chromosome euchromatin vs. heterochromatin heterochromatin remains tightly condensed during interphase but euchromatin becomes less condensed

16 Methods of Regulation: relating to only part of the genome is expressed Condensation: transcription can only occur at euchromatin it is less condensed and accessible to RNA polymerase Examples centromere, Barr bodies Chromosomes puffs associated with rapid transcription.

17 RNA Interference: Chromosome puffs - rapid sites of transcription

18 Methods of Regulation: by specific binding proteins Two opposing functions: some turn the gene on; others turn it off the gene responds to the sum of all the site for binding may be 100 s or 1000 s base pairs away from the promotor

19 Methods of Regulation: noncoding sequences and duplication simple sequence DNA what where chromosome caps what where sequence length

20 Methods of Regulation: noncoding sequences and duplication Intermediate sequence DNA what where example - Gene Families what example - Globin family evolution of globin family of genes pseudogenes

21 Methods of Regulation: noncoding sequences and duplication Single-copy DNA define % which is single copy % which actually codes

22 Methods of Regulation: non-coding sequences Introns: Exons: Introns are transcribed but not present in mrna why range of introns ovalbumin chickens

23 Methods of Regulation: non-coding sequences Introns recombination frequency Introns/Recombination & Globin family

24 Control of gene expression can occur at any step in pathway to a functional protein Background of transcription in eukaryotes: RNA polymerase binds to promoter 3 ->5 DNA strand is template transcribes mrna, trna, rrna not grouped in operons

25 Methods of Regulation: non-coding sequences Background of transcription in eukaryotes: transcription and translation are separated in time and space Cap is added in eukaryotes processing must occur

26 Methods of Regulation: non-coding sequences mrna processing: what precision - prevents frame-shift mutation some instances found in which identical mrna transcripts are processed in more than one way introns become exons & vice-versa creates different functional polypeptides from identical RNA molecules

27 Methods of Regulation: non-coding sequences mrna processing

28 Other Eukaryotic Gene Regulation Since many genes interact with one another, more elements than a single promoter and operator are required for expression of a set of genes.

29 Other Eukaryotic Gene Regulation Controlling Transcription: animation_quiz_-_control_of_gene_expression_in_eukaryotes.html Transcription is controlled by proteins called transcription factors. Two types of transcription factors: those that are responsible for binding RNA polymerase to a promoter. regulatory proteins that can act as activators

30 Other Eukaryotic Gene Regulation Hox (homeobox genes) Homeotic genes are genes that determine which parts of the body form what body parts. Hox genes are examples of homeotic genes. Hox genes code for transcription factors.

31 Other Eukaryotic Gene Regulation RNA Interference: Small interfering RNA segments bind to a protein complex and are able to interfere with a coding sequence on mrna.