The Secret of Life!DNA

04/20/23 2

SOMETHINGHAPPENS

GENE

PROTEIN

The Rap

The Central Dogma

DNA carries the genetic information with is transcribed to mRNA and then translated into proteins.

DNA DNA RNARNA ProteinProtein

DNA

Nucleotides

Nitrogenous Bases

Protein Synthesis Video

The Genome

• Total genetic content of an organism

• Amount of DNA does NOT correlate to complexity

• Tulips - 10x the amount of DNA as humans

• One species of amoeba - 100x as much DNA as humans

• Our genome is full of extra DNA

Human DNA• Humans have about 1013 cells – each with the same amount of

DNA – 3.2 x 109 base pairs – a little over 3 billion

• About 20,000-25,000 genes (Defining a gene problematic -small genes difficult to detect, one gene may code for several proteins, some genes code only for RNA, two genes can overlap, etc.

• Average gene is about 3000 bases

• 99.9% of all nucleotide sequences the same in all people

• Identical DNA but unique cell types and specialties – umm, I wonder how?

• Less than 2% of nucleotides used in making proteins

Genes• Gene-dense "urban centers" mainly composed of

DNA building blocks G and C.

• Gene-poor "deserts" rich in DNA building blocks A and T.

• GC- and AT-rich regions – light/dark bands on chromosomes.

• Genes concentrated in random areas along the genome, with vast expanses of noncoding DNA between.

Genes, con’t.

• Stretches of up to 30,000 C and G bases repeating over and over often occur adjacent to gene-rich areas, forming a barrier between the genes and the "junk DNA." These CpG islands are believed to help regulate gene activity.

• Chromosome 1 has the most genes (2968), and the Y chromosome has the fewest (231).

Genes, con’t.• Coding regions (exons) and non-coding

regions (introns).

• Junk DNA - sequences with no apparent function

• Some non-coding regions may allow for DNA binding proteins that control replication and transcription – regulatory sequences.

• Some DNA sequences are chromosome structures - telomeres and centromeres

• The intron-exon structure of some genes allows alternative splicing of pre-mRNA so different proteins can be made from the same gene. 25,000 human genes encode about 100,000 proteins.

• Some non-coding DNA represents pseudogenes - may serve as raw genetic material for creation of new genes. For example, by duplication of short DNA regions- the major form of genetic change in the human lineage

Gene to Protein – click on picture to access video of spliceosomes

Prokaryotes vs. Eukaryotes

Gene Regulation• Transcriptional control

– Which genes will be transcribed?

• Posttranscriptional control– How is mRNA processed and how fast?

• Translational control– How long does mRNA last in cytoplasm and what

changes are made before it is translated?

• Posttranslational control– How is the protein reconfigured to be functional?

DNA binding proteins determine cell specialization.

Regulation – Lac Operon

Lac Operon video

REGULATION - Eukaryotes

• http://highered.mcgraw-hill.com/olc/dl/120069/bio06.swf

• http://nortonbooks.com/college/biology/animations/ch14p01.htm

Repeated sections of DNA

• Repeated sequences about 50% of genome.• Repetitive sequences thought to have no direct

functions, but over time, they reshape genome by rearranging it, creating entirely new genes, and modifying and reshuffling existing genes.

• During the past 50 million years, a dramatic decrease seems to have occurred in the rate of accumulation of repeats in the human genome.

Transposons - Jumping Genes or Selfish DNA

• Barbara McClintock and corn jumping genes – Nobel Prize

• Miniature inverted-repeat transposable elements or MITES

• 40% of human genome is retrotransposons (copy DNA from RNA) - HIV works this way

• 21% of genome is Long interspersed elements (LINES)

• SINES – short interspersed elements Alu elements – over 1 million copies in human

genome – about 300 base pairs per element

Transposons, con’t

• Diseases that are often caused by transposons include hemophilia, SCID, porphyria, cancer predisposition, and DMD.

• Transposons may have been co-opted by the vertebrate immune system as a means of producing antibody diversity

Consider……….

• 100 million species on the planet – all using the same alphabet!

• But the order of the “chemical letters” varies and so each species has their own unique characteristics

• Various regulatory factors determine how this code is expressed

DNA Music?

• DNA Vibration Music

• Genetic Music

• http://www.dnai.org/a/index.html

This is your homework!