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DNA Notes
Objectives
 Compare the structure of DNA and RNA
 Explain how's DNA's structure facilitates DNA replication
 Describe the process of DNA replication
 Describe the locations, reactants, and products of transcription and translation
 Explain how the languages of DNA and RNA are used to form polypeptides
 Explain how RNA is produced
 Explain how tRNA functions in the process of translation
 Describe the structure and function of ribosomes
 Explain how translation begins
 Describe the step-by-step process by which amino acids are added to a growing polypeptide chain
 Diagram the overall process of transcription and translation
 Describe the major types of mutations and their possible consequences
MYP Unit: Central Dogma (DNA)
Key Concept: Systems
Systems are sets of interacting or interdependent components. Systems provide structure and order in human, natural,
and built environments. Systems can be static or dynamic, simple or complex.
Related Concepts: Transformation & Models
Global Concept: Scientific & Technical Innovation
Statement of Inquiry: The foundation of living systems can be understood through modeling the related forms and
transformations.
CH 10: Molecular Biology of the Gene (p.183)
Date:
DNA Structure (p.186) - knowing structure helps to understand function!
 Deoxyribonucleic Acid is made of nucleotides (monomers) composed of:
1. deoxyribose (sugar)
2. phosphate group
3. nitrogenous base – adenine (A), thymine (T), guanine (G), or cytosine (C)
 purines (A & G) have 2 rings
 pyrimidines (T & C) have 1 ring
 Hydrogen bonds btwn bases hold 2 strands together (steps of ladder)
o A bonds w/ T, G bonds w/ C (At The Gorillaz Concert)
o Purine-pyrimidine bonding ensures uniform width
 Nucleotides join via dehydration synthesis to form a DNA strand
o P of 1 nucleotide attaches to the sugar of another to form the sugar-phosphate
backbone (sides of the ladder)
 Strands are antiparallel – they run in opposite directions
 ALL living things have DNA—differences are in the order of nucleotides
Date:
DNA Replication – the process of DNA copying itself (p.191)
 2 DNA strands are complementary – each can be used to make the other (A-T, G-C)
 Replication is semiconservative – each new DNA molec. has 1 new & 1 old strand
1. Helicases (enzymes) break H bonds b/w complementary strands & separate them at
replication forks
2. DNA polymerases (enzymes) add nucleotides to form new strands thru base-pairing
o Ex. AGTCTG 
3. DNA polymerases proofread for mistakes
Date:
Central Dogma: DNA  RNA  protein (p.192)
 Gene: sequence of DNA that codes for a specific protein
 RNA (ribonucleic acid)… if DNA is the code for proteins, why do we need RNA?
o DNA is in nucleus, but proteins are made at ribosomes, so messenger RNA is
needed to deliver the code
o 3 main differences w/ DNA:
1. Ribose
2. 1 strand
3. Uracil instead of thymine
• Transcription: copying a gene into RNA (p.195)
1. Initiation: RNA polymerase binds to promoter on DNA & unzips it
2. Elongation: 1 strand of DNA is used as a template, & RNA polymerase adds
complementary nucleotides to form RNA
 Ex. if DNA is GTCAAC… RNA is
3. Termination: Terminator sequence signals end of transcription & RNA is released
• mRNA Processing occurs before mRNA leaves the nucleus
o A 5’ GTP cap and polyA tail are added to protect the mRNA from enzymes and
help it reach & bind to the ribosome
o mRNA splicing
 Noncoding regions called introns are removed
 Coding regions called exons are joined (spliced) together
Date:
•
Translation: the decoding of mRNA into a protein
o mRNA codes for AA
o a codon is 3 consecutive mRNA nucleotides that code for a specific AA
o an anticodon on tRNA is complementary to an mRNA codon
o Steps of translation:
1. mRNA binds to ribosome
2. a start codon (AUG) signals the start of protein synthesis
3. tRNA brings specific AA to ribosome
4. anticodon lines up w/ codon
5. peptide bond forms btwn AA forming a polypeptide chain
6. tRNAs bring AA until a stop codon is reached, then polypeptide is released
Central Dogma: DNA
transcription
(nucleus)
mRNA
translation
(ribosome)
polypeptide (protein)
Ex. DNA is ACAATG  mRNA is UGUUAC  tRNAs are ACA & AUG
* genes (DNA)  proteins  traits
Date:
Mutations – mistakes that result in Δ ’s in the DNA nucleotide sequence (p.307)
• May occur during DNA replication, meiosis, or by a mutagen
o Mutagens: chemical or physical agents that cause mutations
 Ex: high-E radiation like X-rays & UV rays
 Carcinogens (cancer-causing chemicals)
• Point mutations – Δ ’s in a single gene that may lead to an altered protein product
1. substitution – one base Δ ’s to another
•
•
2. insertion – an extra base is added
3. deletion – a base is removed
Effects on phenotype (remember, PROTEINS determine phenotype!)
o Silent mutation: DNA Δ ’s but AA sequence does not  no effect
o Missense mutation: 1 AA is Δ ’ed  altered polypeptide
o Nonsense mutation: a codon is Δ ’ed to a stop codon  shortened polypeptide
o Frameshift mutations result from insertion or deletion  nonfunctional polypeptide
 “shift” the reading frame  codons Δ AA Δ  proteins Δ
Chromosomal mutations – Δ’s in # or structure of chromosomes as a result of improper crossing
over or nondisjunction during meiosis