What must DNA do?

1. Replicate to be passed on to the next generation

2. Store information

3. Undergo mutations to provide genetic diversity

DNA structure: A review• Double-stranded helix

• Composed of repeating nucleotides (made of a pentose sugar, phosphate and a nitrogenous base)

• Sugar and phosphate make up the backbone while the bases make up the “rungs” of the ladder

• Bases have complementary pairing with cytosine (C) pairs with guanine (G) and adenine (A) pairs with thymine (T)

DNA structure

How does DNA replicate?

• The two strands unwind by breaking the H bonds

• Complementary nucleotides are added to each strand by DNA polymerase

• Each new double-stranded helix is made of one new strand and one old strand (semiconservative replication)

• The sequence of bases makes each individual unique

DNA replication

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RNA structure and function• Single-stranded

• Composed of repeating nucleotides

• Sugar-phosphate backbone

• Bases are A, C, G and uracil (U)

• Three types of RNA– Ribosomal (rRNA): joins with proteins to form ribosomes– Messenger (mRNA): carries genetic information from DNA to the

ribosomes– Transfer (tRNA): transfers amino acids to a ribosome where they are

added to a forming protein

RNA structure

Sum It Up!!!

• Make a Venn Diagram in your notes to compare and contrast DNA and RNA.

Comparing DNA and RNA

• Similarities: – Are nucleic acids– Are made of

nucleotides– Have sugar-phosphate

backbones– Are found in the

nucleus

• Differences:– DNA is double

stranded while RNA is single stranded

– DNA has T while RNA has U

– RNA is also found in the cytoplasm as well as the nucleus while DNA is not

Proteins: A review• Composed of subunits of amino acids

• Sequence of amino acids determines the shape of the protein

• Synthesized at the ribosomes

• Important for diverse functions in the body including hormones, enzymes and transport

• Can denature causing a loss of function

Proteins: A review of structure

2 steps of gene expression

1. Transcription – DNA is read to make a mRNA in the nucleus of our cells

2. Translation – Reading the mRNA to make a protein in the cytoplasm

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Overview of transcription and translation

Bio

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The genetic code

• Made of 4 bases

• Bases act as a code for amino acids in translation

• Every 3 bases on the mRNA is called a codon that codes for a particular amino acid in translation

What did we learn from the human genome project (HGP)?

• Humans consist of about 3 billion bases and 25,000 genes

• Human genome sequenced in 2003

• There are many polymorphisms or small regions of DNA that vary among individuals were identified

• Genome size is not correlated with the number of genes or complexity of the organisms

What is the next step in the HGP?

• Functional genomics• Understanding how the 25,000 genes function• Understanding the function of gene deserts (82

regions that make up 3% of the genome lacking identifiable genes)

• Comparative genomics• Help understand how species have evolved• Comparing genomes may help identify base

sequences that cause human illness• Help in our understanding of gene regulation

How can we modify a person’s genome?

• Gene therapy - insertion of genetic material into human cells to treat a disorder

– Ex vivo therapy – cells are removed for a person altered and then returned to the patient

– In vivo therapy – a gene is directly inserted into an individual through a vector (e.g. viruses) or directly injected to replace mutated genes or to restore normal controls over gene activity

• Gene therapy has been most successful in treating cancer

Ex vivo gene therapy

DNA technology terms

• Genetic engineering – altering DNA in bacteria, viruses, plants and animal cells through recombinant DNA techonology

• Recombinant DNA – contains DNA from 2 or more different sources

• Transgenic organisms – organisms that have a foreign gene inserted into them

• Biotechnology – using natural biological systems to create a product or to achieve an end desired by humans