1. Replication, Transcription and Translation
Honors Biology
Powerpoint #2 – Chapter 12

2. Warm Up: Base Pairing 1.
A C C T G A 2.
G C T A
G A G

3. What is the DNA ‘backbone’ made of?
Phosphate
and Sugar

4. DNA Replication Nucleotide Hydrogen bonds Sugar-phosphate backbone Key
Adenine (A)
Thymine (T)
Cytosine (C)
Guanine (G)

5. What is DNA replication?
Making a copy of DNA
Why is DNA replication important for cells and multicellular organisms?
Replication allows cells to divide
Forming cells that are genetically identical to the original

6. When does DNA Replication occur?
After the cell grows big enough to divide, during interphase, the “S” phase

7. DNA Replication Original strand New strand Growth Replication fork
DNA polymerase
New strand
Original strand
Nitrogenous bases

8. Important Enzyme #1
Helicase
Unwinds DNA at the replication fork.

9. Important Enzyme #2
DNA Polymerase
Principal enzyme in DNA replication; adds nucleotides to growing strand of DNA and proofreads new strand of DNA

10. Steps in DNA Replication
1. Helicase enzyme breaks the hydrogen bonds between base pairs. This unzips the double helix at a position called the replication fork.
2. There is an abundant supply of nucleotides in the nucleus for the formation of the new polynucleotides.
3. Nucleotides base pair to the bases in the original strands with hydrogen bonds.
4. DNA polymerase joins together the nucleotides together with strong covalent bonds to form a new complementary polynucleotide strand.
5. The double strand reforms a double helix.
6. Two copies of the DNA molecule form behind the replication fork. These are the new daughter chromosomes.

11. Drawings of the steps in DNA Replication
DNA Polymerase
Helicase

12. Some Important DNA Facts
A strand of DNA has 2 ends, the 5’ (5-prime) and 3’ (3-prime) ends.
DNA is ALWAYS copied from 5’ to 3’

13. Some Important DNA Facts
There are multiple ‘bubbles’ of DNA replicated at the same time

14. What is ‘semi-conservative’ replication?
In the new DNA created, one strand is from the original, and one is a new one.
Semi = part of
Conserve = save
Why is ‘semi-conservative’ important?
The DNA is copied EXACTLY generation to generation

15. RNA Where is DNA stored? ______________________ Nucleus
What organelle makes proteins? ______________________
Where are proteins made? ______________________
Nucleus
Ribosomes
Cytoplasm

16. What problem might this pose?
DNA can not take directions for making proteins to the ribosomes.

17. How does RNA solve this problem?
RNA is a disposable copy of DNA that can leave the nucleus

18. RNA has ribose sugar instead of deoxyribose
B. RNA’s structure is very similar to the structure of DNA except for 3 major differences:
RNA has ribose sugar instead of deoxyribose
Nitrogen Base

19. 2. RNA is single-stranded
3. RNA has uracil (U) instead of thymine (T)
DNA: AGTCCTTTAGT
RNA: AGUCCUUUAGU

20. There are three main types of RNA:

21. 1. Ribosomal RNA (rRNA)
rRNA is found in ribosomes, and creates the active site for protein formation

22. tRNA contains the anticodon, and brings amino acids to create proteins
2. Transfer RNA (tRNA)
tRNA contains the anticodon, and brings amino acids to create proteins

23. mRNA provides the template for making proteins
3. Messenger RNA (mRNA)
mRNA provides the template for making proteins

24. III. Transcription
Transcription: Producing RNA by copying part of the DNA’s nucleotide sequence
RNA
DNA
RNA polymerase
Adenine (DNA and RNA)
Cystosine (DNA and RNA)
Guanine(DNA and RNA)
Thymine (DNA only)
Uracil (RNA only)

25. Describe the process of transcription using drawings.
RNA Polymerase rips open the DNA double helix
RNA polymerase grabs bases and lines them up with the original DNA strand
Half of the DNA is copied into a strand of mRNA, then the DNA strand closes, hydrogen bonds reform

26. Transcription

27. How does RNA polymerase know where to start?
Starts when it finds a “promoter”
(specific base sequence)
Found near the beginning of a gene sequence

28. Describe the process of RNA editing
RNA editing is a process that occurs in the nucleus.
It removes introns “intervening sequences” and leaves mRNA with only the exons “expressed sequences.”
After editing a cap and tail are attached and the mRNA is ready to enter into the cytoplasm.

30. IV. Translation
Proteins are long chains of amino acids.
Codon: 3 consecutive nucleotides that “code” for a specific amino acid.
What is the universal “start” codon:
AUG
What are the three “stop” codons?
UGA, UAA, UAG

31. The Genetic Code

32. The Genetic Code

34. Use the genetic code below to translate the following mRNA sequences:
A U G U A U C G G G C A U U U U A A
U C C A U G G A A G U G A U U C C A U A A
C C A U G U G U C C C C A A U G A A A A

35. Use the genetic code below to translate the following mRNA sequences:
A U G U A U C G G G C A U U U U A A
U C C A U G G A A G U G A U U C C A U A A
C C A U G U G U C C C C A A U G A A A A
Methionine (START), Tyrosine, Arginine, Alanine, Phenylaline, STOP.
Serine, Methionine, Glutamic Acid, Valine, Isoleucine, Proline, STOP
Methionine, Cysteine, Proline, Glutamine, STOP, Lysine

36. Translation:
The decoding of RNA into a polypeptide chain (protein)

37. The Central Dogma of Biology is:
DNA  RNA  protein
Where does the first step take place? Nucleus
Where does the second step take place? Cytoplasm

38. F. What is the job of tRNA during translation
F. What is the job of tRNA during translation? Bringing amino acids to the ribosomes and match them up with the correct base on mRNA.
What is an anticodon? The three bases on a tRNA that match with the mRNA codons.
G. What is the role of the ribosome during translation? It is the site of protein assembly

40. H. 1) mRNA is transcribed in the nucleus then travels to the cytoplasm

41. 2) Ribosome grabs mRNA. tRNA brings amino acids to the ribosome
Cytoplasm
mRNA
Start codon
Ribosome
Methionine
Phenylalanine
tRNA
Lysine (amino acid)

42. 3) tRNA matches with complimentary mRNA
3) tRNA matches with complimentary mRNA. Ribosome makes peptide bond between amino acids, and breaks the bond between tRNA and amino acid.
Lysine
Peptide bond
tRNA
Translation direction
mRNA
Ribosome

43. 4) Peptide chain continues to grow until ribosome reaches a stop codon Protein is complete.
tRNA
Ribosome
Growing polypeptide chain
mRNA
Stop codon