1. 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

2. 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.

3. 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!

4. 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.

5. 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?

6. 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

7. 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.

8. 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

9. 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

10. 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.

11. 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

12. Activity: In pairs, complete activity 10.2 “Sequencing a genome”
Quick check qu (pg 362), (pg 364), (pg 370), 16&17 (pg 403)
Chapter review qu 3, 5, 9 (pg )

13. 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?