1. DNA, RNA & PROTEINS
The molecules of life

2. DNA
Deoxyribonucleic Acid (DNA)
is the blueprint for life:

3. DNA structure DNA is a polymer of nucleotides
Each nucleotide composed of
_________________ _________________
_________________

4. Four DNA bases Four kinds of nitrogenous bases: Purine bases
Pyrimidine bases

5. DNA: Complimentary base pairing
Adenine pairs with ________ A
Cytosine pairs with _________ C

6. DNA STRUCTURE
DNA is a ________ helix
Discovered by
Watson and Crick

7. DNA REPLICATION (in the nucleus)

8. DNA Replication First an enzyme DNA topoisomerase untangles the coils
Next: Enzymes called “Helicase” “unzip” the DNA molecule exposing both strands nitrogenous bases.
The DNA is separated into
two strands.

9. DNA Replication
Then: (enzyme) DNA polymerase pairs the bases A-T and G-C.
DNA Polymerase checks work and corrects mistakes ….
Nucleotides are paired
DNA ligase (enzyme) follows behind and bonds the nucleotides together.
Two strands of DNA are created.

10. DNA Replication The process is fast and accurate
an error occurs in only about one of a billion nucleotides.

11. DNA replication begins at specific sites called origins of replication.
The copying proceeds outward in both directions, creating replication "bubbles".
The parent DNA strands open up as daughter strands grow on both sides of each bubble.

12. A eukaryotic DNA molecule has many origins where replication can start at the same time.
This shortens the total time to copy all the DNA. Eventually, all the bubbles merge
End product: two double-stranded DNA molecules, each with one new and one old strand.

13. DNA replication occurs before a cell divides, ensuring that the cells in a multicellular organism all carry the same genetic information.
It is also the mechanism for producing the DNA copies that offspring inherit from parents during reproduction.

14. DNA replication
The resulting double-stranded DNA molecules are identical; proofreading and error-checking mechanisms exist

15. RNA structure and synthesis
RNA: RIBONUCLEIC ACID
Is very similar to DNA
(repeating subunits, nucleotides).
Difference between RNA and DNA:
1. Each nucleotide contains a different sugar:
RIBOSE instead of deoxyribose.
2. Bases are A, G, C, and U (URACIL)
A pairs with U; G pairs with C

16. RNA
3. RNA is single stranded and shorter

17. CENTRAL DOGMA DNA RNA Proteins
transcription
DNA
RNA
Proteins
3 different RNA molecules involved in protein synthesis:
mRNA (messenger RNA)
rRNA (ribosomal RNA
tRNA (transfer RNA)
translation

18. PROTEIN SYTNESIS 1 step: Transcription occurs in the nucleus
2 step: Translation
occurs in the cytoplasm

19. 1st step Transcription: DNA  RNA
Transcription occurs in the nucleus
First: DNA unwinds in a section
Next: mRNA (messenger RNA) is formed by base pairing
with the parent strand of DNA. This begins transcription.
Then: mRNA carries the message about what type of protein to
make from the DNA in the nucleus to the ribosome

20. Transcription Once mRNA is formed, enzymes in the nucleus remove the
Introns (noncoding message)
and leave the
Exons (good message)

21. The Genetic Code
Each 3 consecutive bases on the mRNA is a code word, CODON, that specifies an amino acid.
The genetic code consists of 64 codons,
but only 61 code amino acids.
Three codons act as
signal to stop the process
One codon, AUG, codes
for methionine, and is also
the Start signal for translation.

22. 2nd step Translation: RNA  Protein
Translation: synthesizing a code from amino acids, according to the sequences of the nucleotides in mRNA.
Occurs at the ribosome, in cytoplasm of cell
Ribosomal RNA, rRNA, is needed for protein synthesis – helps mRNA bind to the ribosome
tRNA, brings specific amino acids to the ribosome to be assembled as proteins.

23. Translation
Ribosomes are the sites of ______________

24. Transfer RNA (tRNA) Transport molecule that carries specific
amino acid to a
ribosome
Each tRNA recognizes
the correct codon on
the mRNA molecule

25. Translation

26. Steps in Translation mRNA leaves the nucleus and migrates to ribosome
mRNA binds to small ribosomal subunit
tRNA brings an amino acid to the ribosome, where anticodon on the tRNA binds to the codon of the mRNA
The amino acid bonds to its adjoining amino acid to form a growing polypeptide molecule
The tRNA without the amino acid is released from the ribosome
Other tRNA’s bring amino acids to the ribosome to complete the protein molecule

27. Protein translation

28. Protein synthesis
Occurs in the cytoplasm of the cell

29. Summary:

30. Important
Both DNA and RNA have a direction: one end is the 3’ the other is the 5’ end.
Thus, codons are read in one direction only.
Also, note there is redundancy in the genetic code: the different sequences can specify for the same amino acid.
Example: _______________= Leucine

31. When things go wrong…
Mutations: changes in the DNA sequence, that may be passed along to future generations.
Point mutations: a single base substitution
THE CAT SAW THE RAT
THE CAT SAW THE HAT
Deletion: a small DNA segment is lost
Insertion: a segment of DNA is added
Frame-shift mutation: modification of the reading frame after a deletion or insertion, resulting in all codons downstreams being different.

32. Somatic Mutations
___________ mutations: occur in body cells, or cells that do not lead to gametes.
Somatic mutations that occur in leaves, roots or stems are usually not passed on to future generations…
UNLESS the plant reproduces ____________