1. RNA: The other nucleic acid
Chapter 5 – Protein Synthesis

2. RNA: ribonucleic acid
Nucleic acid formed from nucleotides linked in a long chain
Pentose sugar + phosphate group + nitrogenous base
3 different types of RNA:
Messenger RNA (mRNA) – in the nucleus
Transfer RNA (tRNA) – in the cytoplasm
Ribosomal RNA (rRNA) – in the cytoplasm

3. Differences between DNA & RNA
Type of sugar
Deoxyribose
Ribose
Form
Double strand
Single strand
Nitrogenous bases
A, C, G, T
A, C, G, U (Uracil)
Location
Nucleus
Nucleus & cytoplasm

4. Molecular difference between the 2 sugars

6. Role of RNA
DNA carries the code to produce every protein in the cell, BUT: DNA cannot leave the nucleus
So, RNA plays an important role in the synthesis of proteins
RNA can leave the nucleus & bring the information from DNA to the ribosomes where proteins are produced
Done by mRNA

7. tRNA is responsible for transferring the correct amino acids to the ribosome
rRNA brings the 2 units of the ribosome together to synthesize proteins

8. Proteins – essential for life!

9. Proteins
The human body produces at least different proteins (& maybe more!).
Essential for life.
Each protein has a specific form & function
Generally, proteins are only viable for 2 days before they are broken down into their chemical components & recycled or eliminated as waste

10. Production of a protein takes less than a minute
A cell can produce hundreds each second because it contains thousands of assembly points - ribosomes
Each cell produces billions of proteins

11. All proteins are composed of 20 possible amino acids linked together to form polypeptides
AAs can be attached together in different orientations to produce different proteins
Finished proteins are chains that are folded & rolled up

12. Protein functions Enzymes: facilitate chemical reactions in organisms
Hormones: chemical messengers in the body
Antibodies: defend the body against foreign agents
Storage: make essential substances readily available
Transport: carry substances through body fluids
Structure: form the structural elements of cells, maintain support & shape of the cell, also regulate the passage of substances through the cell membrane

13. Renin regulates blood pressure
BTB protein helps facilitate interaction between other proteins
Renin regulates blood pressure
Hemoglobin helps red blood cells transport oxygen
BRCA1 protects against breast & ovarian cancer
Keratin forms fingernails & hair
Myosin is responsible for muscle contractions
Amylase breaks down complex sugars in saliva & the intestines

14. Protein Alphabet 20 amino acids
Each amino acid is represented on the strand of DNA as a sequence of 3 nucleotides (codon)
More than one codon can code for single amino acid

16. So... segments of DNA carry the codes to create proteins
These segments are called genes
A gene is a sequence of nucleotides that has the potential to be expressed in the form of a protein

17. Protein Synthesis 2 stages
Transcription
Translation
Transcribe: make a copy of the information, preserving the original language
Translate: convert the information to a new language

18. Key Terms:
Codon: sequence of 3 nitrogenous bases in DNA or mRNA which codes for a specific amino acid
Anticodon: group of 3 tRNA bases that combine with corresponding mRNA bases
Start codon: codon that tells the mRNA where to start transcription
Stop codon: signal for mRNA to end transcription

19. Transcription 1st step in protein synthesis
Goal of transcription is to make an exact copy of a small piece of the genome on a strand of RNA
Consists of the construction of RNA along a strand of DNA
Happens in the nucleus of the cell

20. RNA polymerase attaches to a molecule of DNA that will be copied at the “promoter”
Promoter – particular sequence of DNA nucleotides that serves as a binding site for RNA polymerase
Rich in adenine & thymine

21. Nucleotides are added to the exposed strand of DNA (sense strand)
RNA polymerase opens a section of the double helix and begins to synthesize a complementary strand of mRNA
Transcribed strand or sense strand – has the instructions for synthesizing the protein
Non-transcribed strand or anti-sense strand – identical to the synthesized mRNA
Nucleotides are added to the exposed strand of DNA (sense strand)

23. RNA polymerase continues until it reaches a “stop”
Stop – a sequence that signals the end of the section of DNA being copied
After transcription, the mRNA separates from the RNA polymerase, then the RNA polymerase separates from the DNA molecule
The enzyme can continue to another promoter & start a new process of transcription
The 2 strands of DNA reattach to each other

25. Transcription Summary
Initiation: RNA polymerase attaches to DNA at the promoter
Elongation: production of a strand of mRNA
Termination: RNA polymerase reaches the Stop, then releases the mRNA

26. Translation: RNA to proteins
After transcription, mRNA leaves the nucleus
In the cytoplasm, mRNA attaches to a ribosome to form a template
mRNA carries the DNA nucleotide code in groups of 3 (codons), each one codes for an amino acid
Different combinations of codons produce different proteins

27. tRNA reads the mRNA code & attaches the correct amino acid
AAs are floating free in the cytoplasm
tRNA is composed of anticodons which are complementary to the mRNA

29. tRNA lines its anticodon up with the mRNA codon
Amino acids form a chain which will fold up to become a protein
rRNA helps with the formation of bonds between the amino acids
Ribosome releases the new protein
The mRNA breaks down into its individual nucleotides & returns to the nucleus