Download NOTES Ch. 12 DNA

Ch 12 NOTES – MOLECULAR GENETICS - DNA
DNA (DeoxyriboNucleic Acid)– controls by determining the structure of
proteins. DNA contains instructions for making proteins.
 “double helix” structure
 Watson and Crick (1953) built the double helix model using data from
Chargaff and Franklin
DNA is a very long molecule made up of NUCLEOTIDES.
Nucleotides have 3 parts:
1. a simple sugar called deoxyribose
2. a phosphate group (PO4)
3. a nitrogenous base (a carbon ring containing nitrogen)
This is a close-up of a nucleotide:
steps of ladder
sides of ladder
The 4 Nitrogenous bases are:
1. adenine (A)
2. guanine (G)
3. cytosine (C)
4. thymine (T)
Complementary pairs:
A
T (double bond)
C
G (triple bond
Replication – DNA copies itself.
 “unzips” and each strand of DNA serves as a template for the other
strand. A pairs with T and C with G.
 held by weak H bonds
 mRNA – (messenger RNA) – brings instructions from DNA
 rRNA (ribosomal RNA) – binds to mRNA and assembles amino acids
in the correct order
 tRNA (transfer RNA) – delivers amino acids to the ribosomes
The Central Dogma of Biology:
DNA  RNA  PROTEIN
This happens in all living things from bacteria to humans!!
1. Transcription
 DNA unzips
 mRNA made... pairs:
o C---G
o G---C
o T---A
o A---Uracil (U) Different!
 introns removed
 mRNA leaves nucleus and goes to the ribosome
 each set of 3 N-bases is called a codon
DNA
mRNA
Codons
RNA (ribonucleic acid) – takes instructions from DNA then builds proteins
 single-stranded
 sugar is ribose
 contains Uracil instead of Thymine
tRNA
2. Translation – process where mRNA converts to amino acids
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amino acids make up proteins
takes place in the ribosomes
tRNA brings 20 different amino acids to the ribosomes
tRNA anti-codons join with the codons on the mRNA
ribosomes made of rRNA (ribosomal RNA) and proteins
mRNA codon ----- joins with ----- tRNA anti-codon
U
G
U
A
C
A
Exons – (expressed) – regions on DNA that contain information
Introns - (intervening) – regions on DNA that do not code
When mRNA is transcribed both introns and exons are copied. Introns must
be removed. Enzymes cut out the introns, then mRNA leaves the nucleus to
go to the ribosomes.
ALL organisms have the same genetic code so ALL life on earth
evolved from a common origin!
Mutations
 change in the DNA sequence
 can occur in reproductive cells or
 body cells (i.e. stomach cells cannot produce digestive acid or skin
cells lose elasticity)
1. Point mutation – a change in a single base pair in DNA
2. Frameshift mutation – adding or deleting one base of a DNA molecule
3. Chromosomal Alterations
a. Deletions – part of chromosome left out
b. Insertions – part of chomatid breaks off and attaches to sister
chromatid
c. Inversions – part of chromosome breaks off and reattaches
backwards
d. Translocations – part of a chromosome breaks off and is added to
another chromosome.
Causes of Mutations
1. spontaneous – just happen
2. mutagens – factors in the environment
 radiation – xrays, UV light, cosmic rays
 chemicals – dioxins, asbestos, benzene
 high temperatures