EL: To find out what a genome is and how gene expression is regulated Genomics EL: To find out what a genome is and how gene expression is regulated Mr isgro

What is a genome? All of the genetic material (the base pairs) found in one complete set of an organism’s chromosomes. The study of genomes is called genomics.

Does genome size matter? COMMON NAME SPECIES NAME Approx GENOME SIZE (millions of base pairs) Fruit fly Drosophila melanogaster 180 Snake Boa constrictor 2100 Human Homo sapiens 3100 Onion Allium cepa 18000 Lungfish Protopterus aethiopicus 140000 Amoeba Amoeba dubia 670000 Why would a single celled animal like the amoeba need a genome that is about 200 times larger than the human genome? Ans: They carry a lot of junk DNA!

What is a gene? Segment of DNA that codes for formation of a protein Structural genes express structural and/or functional proteins. Regulatory genes are short nucleotide sequences that express proteins that control the activity of structural genes by feedback mechanisms.

Number of genes COMMON NAME SPECIES NAME No. GENES Human Homo sapiens 25000 Mustard plant Arabidopsis thaliana 27000 Fruit fly Drosophila melanogaster 14000 Baker’s yeast Saccharomyces cerevisiae 6000 Gut bacterium Escherichia coli 4000 Should we be offended that a mustard plant has as many genes as a human?

An Overview of Gene Structure Coding Region DNA sequence that will be transcribed from the template strand. 5’ 3’ 5’ STOP Regulatory region START 3’ Promoter region Terminator region

Gene Expression The expression of genetic information is one of the fundamental activities of all cells. Instructions stored in DNA are transcribed and translated into various RNA molecules.

Introns and Exons The coding region in eukaryotes contain: introns - non-coding regions of DNA exons - coding regions of DNA Prokaryotes do not have introns – why? They don’t carry “junk DNA” due to short replication cycles

RNA Processing in Eukaryotic Cells DNA Template Strand Pre-mRNA transcript of DNA template strand Introns are spliced out by spliceosomes leaving only the sequences that will be expressed. This is an example of RNA processing. The introns usually are degraded. The result is a mature mRNA strand that will leave the nucleus to be translated. INTRON INTRON EXON EXON EXON Spliceosome Spliceosome EXON EXON EXON

Genome to proteome The human genome has about 25,000 genes but our proteome (the total number of different proteins) is much larger (~100,000) How can this occur? Many genes can produce more than one protein because the mRNA transcript contains different combinations of exons. This process is called alternative splicing.

Alternative splicing INTRONS Pre-mRNA transcript Possible mRNAs using different combinations of exons Result: when each mRNA is translated, a different protein is produced. EXON 1 EXON 2 EXON 3 EXON 4 EXON 1 EXON 4 PROTEIN 1 EXON 2 EXON 3 EXON 2 EXON 1 EXON 4 PROTEIN 2 EXON 2 EXON 3 EXON 4 PROTEIN 3

Activity: In pairs, complete activity 10.2 “Sequencing a genome” Quick check qu 15-17 (pg 362), 18-23 (pg 364), 24-27 (pg 370), 16&17 (pg 403) Chapter review qu 3, 5, 9 (pg 381-382)

Reflection What learning was new today? What learning was revision or built on what I already know? What did I find most challenging and what strategies will I put in place to help me? What percentage of the class did I spend on task and how can I improve this if needed?