DNA Unit
Structure of DNA
- shape is a double helix
- a long polymer made of smaller units (monomers) called nucleotides
- 4 different types of nucleotides
- Adenine (A)
- Guanine (G)
- Cytosine (C)
- Thymine (T)
- held together by hydrogen bonds
- pairing rules:
A binds with T
G binds with C
Discovery of DNA
- model of shape proposed by Watson and Crick
- won Nobel Prize in 1962
- Rosalind Franklin produced X ray photographs of DNA
- helped Watson and Crick develop their model
- Did NOT win Nobel Prize for her work
Replication
= the process of copying DNA
- happens in the nucleus
- DNA polymerases = enzymes that bond new nucleotides together
- result is two identical strands of DNA
- process has a proofreading system to correct errors
- example:
ATAGCTAGCTTC
TATCGATCGAAG
Replication
ATAGCTAGCTTC
TATCGATCGAAG
&
ATAGCTAGCTTC
TATCGATCGAAG
Transcription
= process of copying information from DNA to mRNA (messenger RNA)
- happens in the nucleus
- RNA polymerases = enzymes that bond nucleotides to a mRNA strand
- one side of the DNA (the template) is used
- new rule: uracil (U) replaces thymine (T)
- U binds with A (but only in RNA)
- example:
ATAGCTAGCTTC (template)
TATCGATCGAAG
Transcription
ATAGCTAGCTTC (template)
UAUCGAUCGAAG (mRNA strand)
Translation
= the process that converts info in mRNA into proteins
- done by ribosomes in the cytoplasm
- codon = 3 nucleotides together
- each represents an amino acid
- example:
mRNA strand broken into codons
UAUCGAUCGAAG
(mRNA strand)
Translation
UAU
Tyrosine
CGA
Arginine
UCG
Serine
Amino Acid Sequence = a protein
Central Dogma
= the flow of information from DNA to RNA to proteins
- involves the three main processes: replication, transcription, translation
Mutations
= a change in an organism’s DNA
- they can be neutral (do nothing), harmful, or beneficial
- substitution mutations = one nucleotide is switched with another
- insertion mutations = added nucleotide to a sequence
- deletion mutations = one nucleotide is deleted from sequence
- mutations in body cells affect only the organism itself and are not passed to offspring
mutations in sex cells (egg and sperm) may be passed to offspring
- most of the time this is bad, but not always
- another source of genetic variation in organisms
- mutagens = agents in the environment that can cause a change in DNA
AAG
Lysine