1. Nucleic Acids & Protein Synthesis Chapter 17
DE Chemistry – King William High School
Nucleic Acids & Protein Synthesis Chapter 17

2. Nucleic acids DNA (deoxyribonucleic acid) – deoxyribose sugars
RNA (ribonucleic acid) – ribose sugars
Both are unbranched polymers of repeating monomer units called nucleotides

3. Components of nucleotide
Base with nitrogen (derivatives of pyrimidine & purine)
In DNA purines = A & G
In DNA pyrimidines = C & T
RNA has the same bases except T becomes U

4. Components… Pentose sugar RNA = ribose DNA = deoxyribose
Nucleosides – when the base and sugar are combined

5. Nucleosides

6. Components… Phosphate group – PO4-3
Nucleotide – nucleosides in which a phosphate group bonds to the OH on carbon 5

7. Primary Structure of nucleic acids
Nucleic acids – 3’ OH group (from sugar) bonds on the 5’ C of the next sugar
This bond is called phosphodiester
Primary structure = sequence of bases
This sequence carries genetic info form cell to cell

8. Primary Structure

9. DNA double helix Watson & Crick Hydrogen bonding
Complementary base pairs (AT & GC)

10. Complementary Base pairs
Write the complementary base sequence for the following DNA segment:
-ACGATCT-

11. DNA Replication DNA’s function is to preserve genetic information
Replication – parent strand separates synthesis of complementary strands begins
Enzyme - helicase

12. RNA v. DNA Most nucleic acid in cells is RNA Sugars in RNA are riboses
The base uracil replaces thymine
RNA is single stranded
RNA is smaller

13. 3 Types of RNA
Messenger – (mRNA) carries genetic info from DNA (nucleus) to ribosomes (cytoplasm)
Transfer – (tRNA)interrupts the genetic info in mRNA & brings specific amino acids (AA) to the ribosomes for protein synthesis…ONLY tRNA can translate genetic info into AA for proteins
Ribosomal – (rRNA) combined with proteins to form ribosomes – the most abundant RNA – cells that synthesize a lot of proteins have 1000s of ribosomes

14. Types of RNA

15. Transcription of mRNA A section of DNA is copied (unwinds) G  C
A  U (remember thymine becomes uracil)

16. Genetic code …consist of 3 nucleotides in mRNA called codons
What is the AA sequence in the following codons?
-GUC AGC CCA-

17. Protein Synthesis Begins when mRNA binds to a ribosome
Start codon is AUG (forms H-bonds with tRNA)
Stops codon is UAA or UGA or UAG (no corresponding tRNA)

18. Genetic Mutations Mutation – a change in a nucleotide sequence
Caused by: x-rays, UV light, chemicals, viruses
Substitution- replacement of one base with another in a DNA strand
Frameshift mutation – a new base is inserted or an existing base is deleted from the strand

19. Effects of Mutations
mRNA has a sequence of codons – CCC AGA GCC-. If a base substitution changes the AGA to GGA…how is the AA sequence affected?

20. Genetic diseases
PKU (phenylketonuria) – DNA cannot direct the synthesis of phenylalanine hydroxylase – brain damage
*if detected in a baby…a diet is prescribed that eliminates all foods that contain phenylalanine.

21. Viruses
Small particles of 3 to 200 genes that can replicate without a host cell
Nucleic acid + DNA or RNA = virus
Invades a host cell…and takes OVER!
Retrovirus = has RNA…must make viral DNA once in the host cell

22. Diseases caused by viruses