1. DNA is used to make Protein: Transcription and Translation
Click here for the Intro Videoclip
Protein Synthesis
DNA is used to make Protein:
Transcription and Translation

2. What's in your genes?
Genes are sequences of nucleotides along DNA strands.
Genes (100s-1000s of nucleotides long) code for polypeptides.
Each DNA strand could hold a couple thousand genes (humans).

3. Polypeptide (protein)
Gene expression
DNA
RNA
Polypeptide (protein)

4. What is Protein Synthesis?
Each gene codes for one polypeptide
Proteins determine our traits:
Enzymes
Hormones
Structural parts of our cells and body
Proteins have to be created by our cells. They are built (with amino acids) based on information stored in our DNA.

5. How does DNA direct protein synthesis? RNA!
RNA = Ribonucleic acid
RNA is very similar to DNA. There are three differences:
The sugar part of RNA is ribose (DNA uses deoxyribose)
RNA substitutes the nitrogenous base URACIL for thymine in DNA
RNA is usually just a single strand, not a double helix.

6. DNA vs. RNA DNA RNA Similarities Nucleic acids Basic unit = nucleotide
Use Bases A, C, G
3 differences
RNA is a single strand
DNA is a double strand
RNA has ribose sugar
DNA has deoxyribose sugar
RNA has uracil
DNA has thymine

7. Types of RNA Messenger Carries message of DNA to the cytoplasm
mRNA rRNA tRNA
Messenger
Carries message of DNA to the cytoplasm
Ribosomal
Combines with proteins to make a ribosome
Transfer
Carries amino acids to the ribosome

8. Bring amino acids to ribosome/mRNA
Concept Map
from to
to make up
also called
which functions to
can be
RNA
Messenger RNA
Ribosomal RNA
Transfer RNA
mRNA
Carry instructions
rRNA
Combine
with proteins
tRNA
Bring amino acids to ribosome/mRNA
DNA
Ribosome
Ribosomes

9. Protein Synthesis 2 Steps: Transcription: DNA  mRNA
Takes place in nucleus
Translation: mRNA  protein
Takes place in cytoplasm

10. Transcription Animation (DNA tube)
Transcription Animation (DNALC)

11. Steps of Transcription
DNA molecule ‘unzips’
Free RNA nucleotides form hydrogen bonds with complementary bases
RNA polymerase bonds RNA nucleotides together.
mRNA detaches from DNA.

12. Transcription RNA polymerase DNA RNA Adenine (DNA and RNA)
Cystosine (DNA and RNA)
Guanine(DNA and RNA)
Thymine (DNA only)
Uracil (RNA only)
RNA polymerase
DNA
RNA

15. Practice transcribing…
If your DNA strand says this…
TAC AGG TCA GAC TTC
What will your complementary RNA strand say?
AUG UCC AGU CUG AAG

16. After transcription comes translation (protein synthesis)
Nuclear membrane
Transcription
Translation
After transcription comes translation (protein synthesis)

17. The DNA Code
The order of bases along a DNA strand (and therefore its mRNA transcript) is a code that specifies the order of amino acids in a protein.
Three bases are read at a time. One triplet (ie AGA) codes for one of 20 amino acids.
Translation is the process by which the nucleotide language of mRNA is translated into amino acid language.

18. DNA triplet
mRNA codon
tRNA anticodon
Amino acid
Translation animation - DNALC

19. Steps of Translation
mRNA enters the cytoplasm and attaches to a ribosome.
1. Translation begins at AUG, the start codon.
2. Each tRNA has an anticodon whose bases are complementary to a codon on the mRNA strand. E.g. codon = AUG, anticodon=?
UAC
3. Two tRNAs at a time bring the correct amino acids to the ribosome

20. tRNA: a closer look
Each tRNAs anticodon is complementary to a specific mRNA codon.

21. Translation mRNA Nucleus Messenger RNA mRNA Lysine Phenylalanine tRNA
Messenger RNA is transcribed in the nucleus.
mRNA
Lysine
Phenylalanine
tRNA
Transfer RNA
The mRNA then enters the cytoplasm and attaches to a ribosome. Translation begins at AUG, the start codon. Each transfer RNA has an anticodon whose bases are complementary to a codon on the mRNA strand. The ribosome positions the start codon to attract its anticodon, which is part of the tRNA that binds methionine. The ribosome also binds the next codon and its anticodon.
Methionine
Ribosome
mRNA
Start codon

22. Steps of Translation
4.The ribosome joins the two amino acids carried by the two tRNAs and breaks the bond between amino acid and its tRNA.
5. The tRNA floats away to pick up new amino acids
6. The ribosome moves along the mRNA, binding new tRNA molecules and amino acids.
7. Translation stops when a stop codon is reached.

23. Translation (continued)
The Polypeptide “Assembly Line”
The ribosome joins the two amino acids—methionine and phenylalanine—and breaks the bond between methionine and its tRNA. The tRNA floats away, allowing the ribosome to bind to another tRNA. The ribosome moves along the mRNA, binding new tRNA molecules and amino acids.
Growing polypeptide chain
Ribosome
tRNA
Lysine
tRNA
mRNA
Completing the Polypeptide
The process continues until the ribosome reaches one of the three stop codons. The result is a growing polypeptide chain.
mRNA
Translation direction
Ribosome

24. Translation mRNA is "read" as codons, combinations of 3 nucleotides.
One codon, AUG, always signals that start of a gene sequence.
Three codons (UAA, UAG, and UGA) are stop signals, ending the formation of a polypeptide.
Genetic code= set of rules giving the correspondence between codons in RNA and amino acids in proteins.
There is redundancy in the code, but no ambiguity.
Take a moment to look at your chart. What observations can you make about this code?

25. Practice: What is the Code?
CCC ?
CGA ?
AGA ?
UGA ?
AAA ?
GGG ?
Proline
Arginine
STOP
Lysine
Glysine

26. Self-Quiz: The Genetic Code
Translate: AUG CGC AAA UUC UGA CGG

27. Translating practice Try these with the wheel: CCC AGU UCA GUC
Use the square table to tell what amino acid each of the following codons corresponds to?
AAA
GCA
UGU
CAG
Lysine
Try these with the wheel:
CCC
AGU
UCA
GUC
Alanine
Cysteine
Proline
Glutamine
Serine
Serine
Valine

28. Summary Watch the Intro video again – you’ll catch more details!
DNA – Secret of Life (Episode 1 of 5) PBS