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
Check out the Animation!
• http://www.dnai.org/a/index.html
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
Check out the Animation!
• http://www.dnai.org/a/index.html
Overview of transcription and translation
Bio
Check out the Animation!
• http://www.dnai.org/a/index.html
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