1. Do Now 3.6 (HW check )
Objectives: 1. Complete & Review DNA replication learning objectives.
2. Define and describe the process of transcription.
Task: 1. A DNA strand has the following sequence:
5’ TAC-CCC-AAA-GCT-ATA 3’
What is the sequence of the complementary strand?

2. The strands of DNA are Antiparallel
Antiparallel means the two strands are parallel, but have opposite orientations.

3. 5’ & 3’: The two different ends of a nucleotide strand
The numbers 5’ and 3’ refer to different carbon atoms in the sugar of a nucleotide.
The 5’ end of a strand has a phosphate attached to it. The 3’ end does not

4. DNA Replication: Key Ideas
ENZYMES:
Helicase “unzips” dsDNA
DNA polymerase builds a complementary strand of DNA.
DNA ligase joins pieces of DNA together
DIRECTION:
Polymerases add nucleotides to the 3’ end of a growing polynucleotide. In other words, new strands are built in the 5’-3’ direction.
The “lagging strand” of DNA is oriented in the 3’-5’ direction and must be built “backwards” in small pieces called Okazaki fragments that must be put together by DNA Ligase.
SEMI-CONSERVATIVE:
Each new dsDNA molecule produced by replication has one old strand and one new strand.

5. “Replisome” (lots of detail!)

6. Transcription Transcription makes an RNA copy of a DNA sequence.
All of a cell’s RNA is made by transcription. (mRNA, tRNA, rRNA, etc.)
RNA molecules process information (DNA is storage)

7. The Big Idea (aka “central dogma”)
Replication
Transcription
Translation
DNA
mRNA
Protein

8. RNA vs. DNA Single strand Ribose sugar
Thymine replaced by Uracil (A=U)

9. RNA’s Shape
Because RNA is single stranded, it can fold up in many different shapes by hydrogen bonding with itself. This is why RNA can have so many different structures and functions.
tRNA
rRNA

10. mRNA
mRNA (messenger RNA) is a single stranded nucleic acid molecule that carries the information in a gene from the nucleus to the cytoplasm. There, it is used by ribosomes as instructions for building a protein molecule.

11. tRNA and rRNA
tRNA and rRNA are used to build proteins during the process of translation which we will learn about soon.
Translation is the process of making a protein using the instructions in an mRNA molecule.

12. DNA & RNA Polymerase
Polymerases are enzymes that make nucleotide polymers. In other words, they make new strands of DNA or RNA.
DNA polymerase makes new DNA strands.
RNA polymerase makes new RNA strands.

13. Polymerases Follow a Template Strand
Notice that RNA polymerase is copying the “template strand” of DNA. The “coding strand” has the same sequence as the new RNA molecule.
Only correctly base-paired matches are added
Polymerases add nucleotides to the 3’ end of a molecule

14. Transcription Process
Promoter: A sequence of DNA preceding the gene to be transcribed where RNA polymerase and other proteins attach before transcription begins.
Transcription makes a COMPLIMENTARY copy of the 3’-5’ DNA strand. The 3’-5’ DNA strand is the template strand.
The DNA coding strand (5’-3’) will therefore have the same sequence of the mRNA molecule being made (except with T, not U)

15. The new RNA molecule built? The DNA template strand read? 5’ 3’ 3’ 5’
Directionality:
What direction is
The new RNA molecule built?
The DNA template strand read?
The DNA coding strand?

16. RNA Polymerase at Work

17. Recap of Key Ideas
Transcription makes an RNA copy of a DNA sequence. mRNA is built in the 5’-3’ direction.
RNA has a different structure than DNA.
Single stranded
Ribose sugar
Uracil replaces Thymine
RNA polymerase performs transcription.
It is the mRNA molecule which exits the nucleus and contains the insturctions used to make a protein.
tRNA and rRNA are other forms of RNA used by a cell to make protein