1. DNA

2. Deoxyribonucleic acid (DNA) is a nucleic acid that contains the genetic instructions used in the development and functioning of all known living organisms & some viruses.
The main role of DNA molecules is the long-term storage of information. DNA is often compared to a set of blueprints or a recipe, since it contains instructions needed to construct other components of cells, such as proteins & RNA molecules. The DNA segments that carry this genetic information are called genes, but other DNA sequences have structural purposes, or are involved in regulating the use of this genetic information.

3. DNA Genes are made of DNA = deoxyribonucleic acid
How could DNA code for everything genes do?
Genes had to carry information from one generation to the next
Genes had to put that information to work by determining the inheritable characteristics of organisms
Genes had to be easily copied, because it is replicated every time the cell divides

4. DNA’s Structure A long molecule made of units called nucleotides
Each nucleotide is made of 3 basic parts:
A 5-carbon sugar called deoxyribose
A phosphate group
A nitrogenous base (There are 4 kinds…)
A (Adenine) T (Thymine)
G (Guanine) C (Cytosine)
Purines Pyrimidines

5. A Single DNA Nucleotide
Phosphate
Group
Deoxyribose
Sugar
Nitrogenous
Base

6. DNA Structure Phosphate Group Deoxyribose Sugar Nitrogenous Base
Weak Hydrogen Bonds

7. Figure 12–7 Structure of DNA
Section 12-1
Nucleotide
Hydrogen bonds
Sugar-phosphate backbone
Key
Adenine (A)
Thymine (T)
Cytosine (C)
Guanine (G)
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8. The Chargaff “rule”
It was discovered that the percentages of guanines (G) and cytosines (C) are almost equal and the percentages of adenines (A) and thymines (T) are almost equal
Erwin Chargaff came up with a “rule” that guanine (G) pairs with cytosine (C) and adenine (A) pairs with thymine (T) (DNA Base Pairing)

9. Let’s pair up DNA! What would pair up with ATCG?
TAGC
What would pair up with ATTAGC?
TAATCG
What would pair up with ATACGGTC?
TATGCCAG

10. The Double Helix
Rosaline Franklin’s x-ray showed that two DNA strands are twisted around each other.
James Watson and Francis Crick used Franklin’s x-ray to make a model of DNA.
Watson and Crick’s model of DNA was a double helix, in which two strands were wound around each other.
Watson and Crick also discovered that hydrogen bonding held the nitrogenous bases together.

11. The two strands of DNA unwind or “unzip” breaking the hydrogen bonds and separating. Then each strand becomes the guide or “template” for the making of a new strand.
A protein called an enzyme called DNA polymerase breaks the nitrogen base bonds and the two strands of DNA separate, polymerizes individual nucleotides to produce DNA and “proof reads” the new DNA.

12. STEP 1 Two original strands of DNA separates by unwinding
Replication fork
Two original strands of DNA separates by unwinding
This occurs through the action of an enzyme that breaks the hydrogen bonds between the strands
The two areas on either end where the DNA separates is the REPLICATION FORK

13. STEP 2
At the replication fork, DNA polymerase moves along the DNA Strands adding nucleotides
As DNA polymerase moves along two strands of DNA form

14. Step 3
DNA Polymerase continues until all the nucleotides have been added
Two new identical molecules of DNA are formed
Another enzyme connects all the pieces of DNA together

15. Proofreading
At the end of Replication, DNA polymerase goes through the DNA to make sure there are no errors
This prevents mistakes in the DNA sequences
Mutations- Change in the sequence of the DNA

16. RNA & Protein synthesis

17. DNA vs. RNA DNA can be compared to the “master plan” of a builder
RNA can be compared to the “disposable copies/blueprints”
It goes to the protein-building ribosome site in the cytoplasm (job site)
RNA is made from the DNA
Single stranded
Contains uracil
Contains ribose
DNA can be compared to the “master plan” of a builder
It stays safely in the nucleus (office)
Double stranded
Contains thymine
Contains deoxyribose

18. How are genes expressed?
Genes are coded DNA instructions that control the production of proteins within the cell.
The 1st step in decoding the DNA is to copy part of the nucleotide sequence into RNA
RNA = ribonucleic acid
The RNA’s make proteins

19. What is RNA? RNA consists of a long chain of nucleotides (like DNA)
A sugar called ribose
A phosphate group
A nitrogenous base
Adenine (A) Uracil (U) … not Thymine (T)
Cytosine (C) Guanine (G)
RNA is single-stranded

20. RNA Nucleotide
Phosphate
Group
Ribose
Sugar
Nitrogenous
Base

21. RNA Structure
Phosphate Group
Nitrogenous Base
Ribose Sugar

22. Types of RNA RNA’s assemble amino acids into proteins
There are 3 types of RNA
Messenger RNA (mRNA)
Ribosomal RNA (rRNA)
Transfer RNA (tRNA)

23. Messenger RNA Copies instructions in genes
Serves as a “messenger” from the DNA to the cell

24. Ribosomal RNA Ribosomes make proteins
Ribosomes are made of proteins and contain their own RNA

25. Transfer RNA
Transfer amino acids to ribosomes based on specified codes in mRNA

26. How is RNA made? RNA is made by transcription: DNA to RNA
Transcription uses an enzyme RNA polymerase
During transcription, RNA polymerase binds to DNA and separates the DNA strands, RNA polymerase then uses one strand of DNA as a template (stencil) from which nucleotides are assembled into a strand of RNA
For example: DNA: ACTGTGGACCT
RNA: UGACACCUGGA
TRANSCRIPTION

27. The Genetic Code
Remember: Proteins are chains of amino acids called polypeptides
The order of the amino acids determines the properties of the protein
The instructions for making different amino acids are in the mRNA = the genetic code
The genetic codes is read 3 letters at a time, so each “word” is 3 bases long = codon

28. How are proteins made?
Proteins are made by translation: RNA to protein
Translation occurs in the cytoplasm
During translation, the cell uses information from mRNA to make proteins.
mRNA instructs amino acids on tRNA to join together in the ribosome containing rRNA

29. What is tRNA again? Transfer RNA brings amino acids to the ribosome.
One end of the tRNA has an amino acid, the other end has 3 bases called the anticodon, that are complementary to one of the mRNA codons
Amino acid
Anticodon

30. Codons
Three consecutive nucleotides that specify a single amino acid that is to be added to the polypeptide
For example:
RNA: UCGCACGGU
Codons: UCG-CAC-GGU
Amino acids: Serine-Histidine-Glycine
There are 64 possible codon combinations, but there are only 20 amino acids!
*More than one codon can code for an amino acid

31. When does it begin or end?
There is 1 “start” codon that initiates protein synthesis if it is the 1st codon (otherwise it codes for an amino acid)
AUG
There are 3 “stop” codons that do not code for any amino acid and signify the end of a polypeptide.
UAA
UAG
UGA

32. Let’s try to make a protein!
DNA: CCAGATAGGTTT
mRNA: GGUCUAUCCAAA
codons: GGU-CUA-UCC-AAA
tRNA: CCA-GAU-AGG-UUU
Amino acids for the mRNA codons
on tRNA’s: Glycine-Leucine-Serine-Lysine