1. DNA Structure and Replication
Biology SL – Melinda Ragsdale

2. DNA Structure – Review Composed of nucleotides that are complimentary
Base pairs are Adenine – Thymine Cytosine-Guanine
DNA Backbone made of repeating units of 5-carbon sugar and phosphate covalently bonded
Strands held together by hydrogen bonds between base pairs

3. DNA Replication
Replication is semi-conservative – DNA splits into two individual strands each becoming the template for the new strand.
Many enzymes are involved in replication
DNA Helicase – job is to unzip DNA
DNA Polymerase III – links nucleotides together and acts as a proof-reader
DNA ligase – links pieces of DNA together (specifically Okazaki Fragments which will be explained later)
RNA Primase – a small, temporary piece of RNA that “primes” the location of replication
DNA Polymerase I – removes the RNA primer

4. DNA Replication – The Basics
DNA has two ends – the 5’ and 3’
5’ end always starts with a phosphate while 3’ ends with the sugar
Because the strands are complimentary, one strand always runs 5’ – 3’ while the other runs 3’ to 5’
DNA replication always occurs in a 5’ -3’ direction so one strand can be copied faster than the other
Replication fork – the place where the DNA splits and replication is initiated

5. Leading and Lagging Strands
Since DNA is copied in a 5’ – 3’ direction, one strand of DNA can be copied constantly. We refer to this as the leading strand.
The reverse strand is also copied in a 5’-3’ direction but it is forced to do so in a disjointed manner. We refer to this as the lagging strand because the copying occurs at a much slower rate.
Okizaki fragments – Small pieces of DNA that have been copied
DNA Ligase – the enzyme that pieces these small fragments together into a single strand.

8. RNA AND PROTEIN SYNTHESIS
Converting the blueprints into protein

9. Central Dogma of Genetics
Reproduction requires the transmission of genetic information from parent to offspring
Genes are discrete units of heredity that is coded by base pair sequences
Genes code for amino acids
Amino acids build proteins

10. How is RNA different from dna?
RNA = RIBONUCLEIC ACID
MADE UP OF NUCLEOTIDES (JUST LIKE DNA)
SINGLE STRANDED INSTEAD OF DOUBLE
MADE IN THE NUCLEUS
DOESN’T STAY IN THE NUCLEUS LIKE DNA – IT MOVES INTO THE CYTOPLASM
RNA copies DNA and helps make protein
THYAMINE IS NOT IN RNA → REPLACED BY URACIL

11. THREE DIFFERENT TYPES OF RNA PRODUCED
Ribosomal RNA (rRNA) – combines with protein to form ribosomes
Transfer RNA (tRNA) – brings (transfers) amino acids to the ribosome for protein assembly.
Messenger RNA (mRNA) – the instructions (order of assembly) of the protein to be made.

12. DNA TRANSCRIPTION
TRANSCRIPTION – DNA IS USED AS A TEMPLATE TO MAKE mRNA
Occurs in a 5’ – 3’ direction
GENE – THE SECTION OF DNA THAT IS COPIED
GENES CONTAIN CODES FOR SPECIFIC PROTEINS THAT CONTROL “TRAITS” IN THE HUMAN BODY

13. Sense vs Antisense
Sense strand of DNA codes for a strand of protein but it is NOT copied by mRNA
Antisense (or nonsense) strand acts as the template for mRNA
Adenine pairs with Uracil (instead of Thyamine)
Cytosine pairs with Guanine

14. TRANSCRIPTION THE PROCESS OF mRNA COPYING A SECTION OF DNA
THAT SECTION OF DNA THAT IS COPIED IS A GENE
GENES ALWAYS HAVE THREE PARTS:
PROMOTER REGION – TELLS RNA POLYMERASE WHERE TO BEGIN
CODING REGION – THE ACTUAL SECTION THAT IS COPIED DOWN
TERMINATOR – TELLS RNA POLYMERASE WHEN TO STOP

15. RNA EDITING
WHEN mRNA IS MADE, SOME PARTS ARE USEFUL WHILE OTHER PARTS NEED TO BE REMOVED
INTRONS – PARTS OF THE GENE THAT ARE NOT USEFUL → THEY ARE REMOVED
EXTRONS – USEFUL PARTS OF THE GENE

17. THE GENETIC CODE
THE NUMBER AND ORDER OF AMINO ACIDS DETERMINE THE PROTEIN
SIMILAR TO OUR ALPHABET
AMINO ACIDS = LETTERS
PROTEINS = WORDS
CODON – THREE NUCLEOTIDES ON mRNA THAT SPECIFY WHICH AMINO ACID IS USED TO MAKE THE PROTEIN

18. TRANSLATION
TRANSLATION – MESSGENER RNA USES tRNA AT THE RIBOSOME (rRNA) TO CREATE PROTEIN
STEPS IN TRANSLATION
RIBOSOME BINDS TO THE MRNA
TRNA BRINGS THE CORRECT AMINO ACID TO THE RIBOSOME
THE PROTEIN GETS ASSEMBLED ONE AMINO ACID AT A TIME