1. RNA & Protein synthesis

2. DNA vs. RNA DNA can be compared to the “master plan” of a builder
RNA can be compared to the “disposable copies/blueprints”
It goes to the protein-building ribosome site in the cytoplasm (job site)
RNA is made from the DNA
Single stranded
Contains uracil
Contains ribose
DNA can be compared to the “master plan” of a builder
It stays safely in the nucleus (office)
Double stranded
Contains thymine
Contains deoxyribose

3. How are genes expressed?
Genes are coded DNA instructions that control the production of proteins within the cell.
The 1st step in decoding the DNA is to copy part of the nucleotide sequence into RNA
RNA = ribonucleic acid
The RNA’s make proteins

4. What is RNA? RNA consists of a long chain of nucleotides (like DNA)
A sugar called ribose
A phosphate group
A nitrogenous base
Adenine (A) Uracil (U) … not Thymine (T)
Cytosine (C) Guanine (G)
RNA is single-stranded

5. RNA Nucleotide
Phosphate
Group
Ribose
Sugar
Nitrogenous
Base

6. RNA Structure
Phosphate Group
Nitrogenous Base
Ribose Sugar

7. Types of RNA RNA’s assemble amino acids into proteins
There are 3 types of RNA
Messenger RNA (mRNA)
Ribosomal RNA (rRNA)
Transfer RNA (tRNA)

8. Messenger RNA Copies instructions in genes
Serves as a “messenger” from the DNA to the cell

9. Ribosomal RNA Ribosomes make proteins
Ribosomes are made of proteins and contain their own RNA

10. Transfer RNA
Transfer amino acids to ribosomes based on specified codes in mRNA

11. Section 12-3
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12. How is RNA made? RNA is made by transcription: DNA to RNA
Transcription uses an enzyme RNA polymerase
During transcription, RNA polymerase binds to DNA and separates the DNA strands, RNA polymerase then uses one strand of DNA as a template (stencil) from which nucleotides are assembled into a strand of RNA
For example: DNA: ACTGTGGACCT
RNA: UGACACCUGGA
TRANSCRIPTION

13. The Genetic Code
Remember: Proteins are chains of amino acids called polypeptides
The order of the amino acids determines the properties of the protein
The instructions for making different amino acids are in the mRNA = the genetic code
The genetic codes is read 3 letters at a time, so each “word” is 3 bases long = codon

14. How are proteins made?
Proteins are made by translation: RNA to protein
Translation occurs in the cytoplasm
During translation, the cell uses information from mRNA to make proteins.
mRNA instructs amino acids on tRNA to join together in the ribosome containing rRNA

16. What is tRNA again? Transfer RNA brings amino acids to the ribosome.
One end of the tRNA has an amino acid, the other end has 3 bases called the anticodon, that are complementary to one of the mRNA codons
Amino acid
Anticodon

17. Codons
Three consecutive nucleotides that specify a single amino acid that is to be added to the polypeptide
For example:
RNA: UCGCACGGU
Codons: UCG-CAC-GGU
Amino acids: Serine-Histidine-Glycine
There are 64 possible codon combinations, but there are only 20 amino acids!
*More than one codon can code for an amino acid

18. When does it begin or end?
There is 1 “start” codon that initiates protein synthesis if it is the 1st codon (otherwise it codes for an amino acid)
AUG
There are 3 “stop” codons that do not code for any amino acid and signify the end of a polypeptide.
UAA
UAG
UGA

19. Let’s try to make a protein!
DNA: CCAGATAGGTTT
mRNA: GGUCUAUCCAAA
codons: GGU-CUA-UCC-AAA
tRNA: CCA-GAU-AGG-UUU
Amino acids for the mRNA codons
on tRNA’s: Glycine-Leucine-Serine-Lysine