Chapter 11 DNA Structure and Replication RNA and Protein Synthesis 2017.ppt

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
• 3 different RNA molecules involved in
protein synthesis:
mRNA (messenger RNA)
rRNA (ribosomal RNA
tRNA (transfer RNA)
transcription
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
1. mRNA leaves the nucleus and migrates to ribosome
2. mRNA binds to small ribosomal subunit
3. tRNA brings an amino acid to the ribosome, where
anticodon on the tRNA binds to the codon of the
mRNA
4. The amino acid bonds to its adjoining amino acid to
form a growing polypeptide molecule
5. The tRNA without the amino acid is released from the
ribosome
6. 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 ____________