1. THE ROLES OF DNA

2. First Function: DNA Replication
The Cell makes an identical copy of the DNA
Takes place during the S phase of the Cell Cycle
Carefully controlled by a group of enzymes

3. The Enzymes separate or unwind the 2 strands of DNA
make 2 new strands by adding nitrogen bases according to the base pair rule
the new strands are called “complimentary”

4. Write the Compliment DNA Code
Strand of DNA
_________________________________
ATT CGC ATC GGA TTC GCA AAC TTA
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Complimentary Strand of DNA

5. Write the Compliment DNA Code
Strand of DNA
_________________________________
ATT CGC ATC GGA TTC GCA AAC TTA
TTA GCG TAG CCT AAG CGT TTG AAT
__________________________________
Complimentary Strand of DNA

6. Mitosis
Once DNA replication is complete a cell has duplicated all its genetic information
The cell is ready to enter cell division
Each daughter cell has an identical set of chromosomes
46 chromosomes

7. DNA Replication DNA replication is called semi-conservative
That means the DNA for each daughter cell consists of 1 one old DNA strand and 1 new strand.
This helps reduce the number of copy errors.

8. DNA REPLICATION

9. Review DNA Replication
An exact copy of a cells chromosomes are made
Requires enzymes
Occurs during S phase
Base pairs join following the base pair rule to form the new DNA strands
A- T and C- G
Results: each new daughter cell has a genetically identical set of chromosomes to the parent cell

10. Color DNA Replication Look back at your DNA structure coloring sheet for nitrogen base shape
KEY
Phosphates pink
Deoxyribose blue
Thymine orange
Adenine green
Guanines purple
Cytosine yellow
The boxed section shows 2 new strands of DNA. Color the old strands red and the new strands green

11. All Cells Need the Exact DNA
Every daughter cell needs an exact copy of DNA because it contains the “Blue-print” of life or the instructions to make a living organism!

12. 2nd Function: Protein Synthesis
To decode the genetic information contained in DNA, the cell uses a molecule called RNA
RNA = ribonucleic acid
Carries out the instructions coded in DNA to make a protein
What does RNA look like?
We need to compare it to DNA for the answer……

13. DNA vs. RNA DNA Sugar = deoxyribose Double stranded
Contains 3000 genes
Bases = A T C G
RNA
Sugar = ribose
Single stranded
Contains 1 gene
Bases = A U C G
U= uracil

14. How Is RNA made?

15. RNA is made in a process called: Transcription
Part of the nucleotide sequence of a DNA molecule is copied into RNA
This sequence of DNA copied is called a gene
DNA is a template from which RNA can be made

16. RNA Sequence RNA is constructed out of molecules in the Cell
Requires enzymes
RNA polymerase
Produces a strand of RNA one base at a time
RNA bases match the bases on DNA

17. Base Pair Rule for DNA coding into RNA
RNA has Uracil (U) instead of Thymine (T)
The base Adenine on DNA codes for Uracil on RNA
The base Thymine on DNA codes for Adenine on RNA
The base Guanine on DNA codes for Cytosine on RNA
The base Cytosine on DNA codes for Guanine on RNA

18. Lets Practice
DNA ___________________________ AAT CGT CTT GAC TGC TTC ____________________________ RNA What is the complimentary strand of RNA?

19. DNA transcribed into RNA
AAT CGT CTT GAC TGC TAC
UUA GCA GAA CUG ACG AUG
___________________________
RNA

20. New Strand is called mRNA
Messenger (m) RNA = “cheap” copy of DNA
Cell uses mRNA to transport DNA’s message

21. Questions 1. What is the purpose of mRNA?
2. How does mRNA carry DNA’s Message?
3. What does the message “say”?

22. 1. What is the purpose of mRNA? mRNA Helps the Cell Make Proteins
After DNA has coded for a strand of mRNA, it leaves the nucleus and travels to the ribosome
At the ribosome mRNA’s code is translated into a protein
mRNA codes for a specific
protein by copying the DNA code!

23. 2. How does mRNA carry DNA’s Message?
RNA contains 4 different nitrogen bases (A,U,C,G)
These 4 bases carry the instructions from DNA to assemble amino acids
3 nitrogen bases on RNA code for 1 amino acid
The 3 nitrogen bases (AAA) are called a codon or a “word” in the genetic message
How many amino acids would this code for?
AAA CAC GGU

24. 3. What Does DNA”s Message “Say”?
the order of nitrogen bases on DNA specify a specific amino acid chain
The chain of amino acids forms a protein
If the DNA sequence changes then a different amino acid chain is made, creating a different protein

25. Amino Acids
Basic structure

26. 20 Amino Acids

27. Protein: Chain of Amino Acids
How is a protein actually made?

28. Steps to Making a Protein Step 1: Transcription
In the nucleus DNA unwinds at a very specific point
mRNA is assembled by matching the bases on DNA following the base pair rule
mRNA leaves the nucleus
This process is called transcription
DNA mRNA

29. Step 2: Translation At The Ribosome
1.mRNA arrives at the ribosome
2. mRNA’s code is read 3 bases at a time called a codon AAA = 1 codon
3. 1 codon represents 1 amino acid
AAA = lysine
CAT = histidine
GGU = glycine
4. As the codon’s are read, a chain of amino acids form
5. The result is a molecule called a polypeptide chain

30. Translation
The nucleotides in mRNA are translated into a polypeptide chain 1 Amino Acid at a time.
Polypeptide chain Amino Acids
mRNA Ribosome

31. Protein Synthesis
Transcription Translation
peptide bond video

32. Polypeptide Chain to Protein
Polypeptide Twists and Folds Functional Protein Chain

33. Big Picture: Protein Synthesis
The section of DNA (gene) directs the synthesis or making of a functional protein from inside the nucleus by using mRNA and a ribosome.

34. The Genetic Code A stretch of DNA: AAT GAC CAT GGC TAG
codes for a different protein than a stretch that reads:
GGG CCA TAG CGT ATT
The 4 bases have endless combinations that form the 20,000 different proteins the human cell can synthesize

35. Genes and Proteins Genes:
control your physical traits by coding for proteins that have specific functions in the body
Proteins
Molecules that control all cell functions
DNA Video Clip

36. Putting It all Together Genes to Proteins
Control physical characteristics: 3 examples
A gene controls flower color by coding for an enzyme that produces a pigment
A gene coding for an enzyme that controls blood type by producing complex molecules in the RBC
A gene codes for a protein that regulates the rate and pattern of growth throughout an organism.

37. Gene Expression
A gene that is transcribed into mRNA is said to be expressed or turned on
A gene that is not being transcribed is said to be unexpressed or turned off
Deciding which genes to turn on and which genes to turn off depends on the needs of the cell at that time.