Who is smarter and does more tricks you or a bacteria? YouBacteria How does my DNA compare to a prokaryote? Show-off

Regulation of Eukaryotic Gene Expression  Who is more interesting you or a bacteria?  Ans: YOU  Who has more genes?  Ans: YOU  Who is more interesting you or a corn plant?  Ans: YOU  Who has more genes you or a corn plant?  Ans: A corn plant (32,690 vs. ≈ 23,000)  How can you have fewer genes than a corn?  Ans: It is not only what you have it is how you use what you have, i.e. how your genes are expressed

COMPARISION OF PROKARYOTIC VS EUKARYOTIC CELLS Bacteria exist as single cells Eukaryotic cells: Specialized roles within organism Retinal eye cell

EUKARYOTES HAVE MUCH MORE DNA THAN PROKARYOTES... Prokaryotic DNA Eukaryotic DNA But Prokaryotic DNA has a much higher gene density; Only ≈ 1.5 % of Eukaryotic DNA actually codes for proteins. Eukaryotic DNA actually codes for proteins. Prokaryotic DNA Eukaryotic DNA Example: E. coli 4.5 Mbases; humans 3,200 MB

Nearly all genes in prokaryotes are expressed at some time in the life of the cell IN EUKARYOTIC CELLS WITH SPECIALIZED ROLES, ONLY ABOUT 20-60% OF THE GENES ARE EXPRESSED. %GENESExpressed%GENESExpressed In Eukaryotes as little as 0.20 x 1.5 or 0.30 % of the DNA is typically actively coding for protein in a given cell. High end 0.60 x 1.5 = 0.90%.

Key differences in gene expression between prokaryotes and eukaryotes Eukaryotes Eukaryotes Multi-celled organisms with cells that carryout specialized tasks Typically much larger genome than prokaryotes Approximately 20-60% of genes are expressed in a given cell. ≈ 1.5 % coding DNA; Large amount of noncoding DNA. Prokaryotes Prokaryotes Composed of single cell that must carry out all functions Very small genome Nearly all genes expressed at some point Almost all DNA codes for protein

Link to Chromosome 11 Flyover Link to Chromosome 11 Flyover DNA Interactive – Animations DNA molecule – How much DNA codes for protein? DNA Interactive – Animations DNA molecule – How much DNA codes for protein? DNA Interactive Interviews – Eric Lander (MIT) Bacteria vs. Eukaryotic gen

Fig Exons (regions of genes coding for protein or giving rise to rRNA or tRNA) (1.5%) Repetitive DNA that includes transposable elements and related sequences (44%) Introns and regulatory sequences (24%) Unique noncoding DNA (15%) Repetitive DNA unrelated to transposable elements (15%) L1 sequences (17%) Alu elements (10%) Simple sequence DNA (3%) Large-segment duplications (5–6%) Most eukaryotic DNA consists of noncoding repeats (green areas) Repeat regions are used for DNA fingerprinting Very tiny differences in sequence between different individuals in exon regions

UPDATE SEPT Paper published in Nature summarizing results of ENCODE (Encyclopedia of DNA Elements) now suggests that approximately 80% of our DNA is involved in regulating the expression of our genes. Regulation occurs through a variety of mechanism including transcription factor activity and small interfering RNA sequences. More on these later...

Review Questions Describe the DNA sequences in eukaryotes Ans: Only 1.5 % potentially codes for proteins or rRNA or tRNA. Some noncoding DNA serves regulatory functions (eg promoter or enhancers) The majority consists of repeats whose exact function is unclear. What % of genes in a typical eukaryotic cell are actively expressed? Approximately 20-60%. What region of the eukaryotic DNA is used for DNA fingerprinting? Can you use the DNA fingerprinting method for bacteria? Noncoding Repeat; No, prokaryotes do not have extensive noncoding repeats.

Review Questions Describe the DNA sequences in eukaryotes Ans: Only 1.5 % potentially codes for proteins or rRNA or tRNA. Some noncoding DNA serves regulatory functions (eg promoter or enhancers) The majority consists of repeats whose exact function is unclear. How do the DNA sequences in a liver cell compare to those in an eye cell? They are exactly the same. The differences in cell structure and function are due to differences in expression of the genes. What % of genes in a typical eukaryotic cell are actively expressed? Approximately 20-60%

How much variation in DNA sequences is present in these different cells in your body? ANS: ANS: NONE: They all have identical DNA sequences however the genes are expressed differently. White Blood Cell Liver Cell Eye Cell Nerve Cell

How similar you to a chimp? In terms of anatomy? In terms of behavior? Physicially not very similar, some similarities, a lot of differences Most humans behave differently than chimps

How similar are Humans and chimps in terms of DNA sequences? Pretty similar ( % similar; some differences in chromosome structures).

How similar are the DNA sequences of people of different race/sex? Extremely similar (99.9% the same). Most differences are not in sequences themselves but in # of repeats of noncoding regions.

How can differences in phenotypic expression be explain on a molecular level?

Multiple Mechanisms for changing Phenotypic expression Change proteins themselves

Multiple Mechanisms for changing Phenotypic expression  Change timing of when proteins are made  Change amount of protein made or whether protein is made at all

Are the DNA sequences of the genes that code for beak shape in Darwin’s Finches different in birds with different shaped beaks? Are there any DNA differences between birds with different shape beaks? NO – all Darwin’s Finches have identical sequences in all of the genes that encode collagen proteins that form the beaks. There are small differences in DNA sequences of proteins that regulate gene expression. It is the timing of when the genes are expressed during development of the embryo and the extent of expression that matters; For example a delay of 24 hours in the timing of gene expression makes a long thin peak into a short fat beak.(differences in when transcription factors are present controls timing)..

One gene can change the level or timing of expression of many other genes

Implication for Evolution You don’t need many mutations to get a different body structure or a even a different species if the mutation impacts gene expression. You don’t need many mutations to get a different body structure or a even a different species if the mutation impacts gene expression. In other words, mutations in regulatory proteins can have huge impacts by effecting the timing or degree of expression of many, many proteins.

Why is understanding Regulation of Gene Expression of Eukaryotic Genomes important? Ans: Genetic Basis of Differences between different people is most likely based much more on differences in how our genes are expressed rather than specific sequence differences within our genes. Mutations in genes that regulate other genes (e.g. transcription factor proteins) are most likely far more important than differences within non-regulatory genes. Mutations in genes that regulate other genes (e.g. transcription factor proteins) are most likely far more important than differences within non-regulatory genes.