1. Unit 6: DNA & Protein Synthesis
Ch. 28: DNA—Life’s Code
Watson & Crick
Watson worked for Cold Spring Harbor & headed up Human Genome project in 90s
DNA = Deoxyribonucleic Acid

2. Describing DNA Who first described DNA?
James Watson & Francis Crick
What shape did they use to describe DNA?
double helix
Video
Rosalind Franklin & Maurice Wilkins used x-ray diffraction (scattering) to show DNA was helix shape RF died of cancer in 30s due to x-ray exposure… no Nobel prize b/c not alive…
James Watson and Francis Crick first described DNA as double helix structure (“backbone” sides/uprights = sugar & phosphate; rungs = N bases) fact that A & T same amts & G&C same amts helped them figure out how 2 chains are joined.

3. DNA is a Polymer… What is the monomer that repeats to make DNA?
nucleotide
What is the monomer that repeats to make DNA? A nucleotide
Monomer = small molecule Polymer = large molecule made of repeated monomers

4. What are the parts of a nucleotide?
phosphate group
sugar (deoxyribose)
nitrogenous base
4 kinds:
Adenine (A)
Thymine (T)
Guanine (G)
Cytosine (C)
base gives name to nucleotide
adenine, thymine, guanine, or cytosine
Trick to remember the 4 types of nitrogen bases: All the good children. (adenine, thymine, guanine, cytosine)
The nitrogen base gives its name to the nucleotide. (ex. adenine nucleotide contains adenine base)

5. A Model of DNA Is a DNA molecule single-stranded or double stranded?
What parts make up the strands?
“backbone”/sides
sugars & phosphates
“rungs”/steps
nitrogenous bases
always paired as:
A - T
G - C
DNA Structure Video
2 chains of nucleotides bonded together… Double helix shape… similar to a rope ladder wrapped around an invisible pole
Nitrogenous bases (“rungs”) are in pairs held together by hydrogen bonding
(Erwin) Chargaff's Rule Always pair (complementary bases) A – T & G – C (triple bond)…. b/c A & T same amt, G & C same amt
All the good children. (adenine, thymine, guanine, cytosine)

6. Strands are complementary (A-T & G-C) & antiparallel (opposite directions/upside down)
The 2 strands are antiparallel (facing opposite directions/upside down) b/c if not, bases would not be next to one another & couldn’t bond.
Phosphate group bonds to sugar to form backbone
N-Bases (1 from each side) Hydrogen bond to make rungs

7. Where is DNA found in eukaryotic cells?
DNA is contained in chromosomes (chromatin) within the nucleus
sugar-phosphate “backbone” & nitrogenous base “rungs”

8. DNA Replication What is another word for replication?
copying
Why must DNA replicate?
so when cell divides, each new cell gets a copy of DNA
Another word for replication??? copying
Why must DNA replicate? DNA must replicate before cell division so that each daughter cell receives an exact copy.

9. DNA Replication When does DNA replicate? Where does DNA replicate?
before the cell divides (before mitosis or meiosis)
Where does DNA replicate?
inside the nucleus
When does it replicate? Before cell divides (before mitosis &meiosis)
Where does it replicate? In the nucleus (for eukaryotic cells)

11. What are the steps in DNA replication?
1. DNA molecule unzips between bases forming two “parent strands”
DNA replication occurs before cell division and it goes through a series of steps to duplicate new DNA molecules.
Helicase, an enzyme, helps to unzip the DNA molecule.

12. What are the steps in DNA replication?
2. The “parent” strands act as templates (guides)…
“new” nucleotides are paired up with the complementary base on the “parent” strand
forming a complementary daughter strand
ex. “G” pairs with “C” T C

13. What are the steps in DNA replication?
3. Now, there are 2 exact copies of the original DNA molecule.
& when the cell divides, each “new” daughter cell gets a copy

14. What are the steps in DNA replication?
DNA Replication Video

15. Let’s Practice… Predict the next base…

16. Let’s Practice… Finish the replications…

17. Let’s Practice… Finish the replications…

18. Deoxyribonucleic Acid vs. Ribonucleic Acid
DNA
RNA
sugar = deoxyribose
sugar = ribose
double stranded
single stranded
CANNOT leave nucleus
Can move between nucleus & cytoplasm
N bases = adenine, thymine, guanine, cytosine
N bases = adenine, uracil, guanine, cytosine

19. The DNA Code & Protein Synthesis
What is a gene?
section of DNA that codes for synthesis of a specific protein
Which part of DNA carries the code for a protein?
the nitrogen bases
& their order
change sequence  amino acid (usually) changes  & protein made (usually) changes
Genes determine the type of proteins our bodies make. Genes, therefore, control a huge variety of factors that help make us unique individuals. Genes play a part in determining everything from the color of your hair and eyes to the size of your feet.
What part of DNA actually carries the code? The sequence of bases along one of the 2 chains of a DNA molecule carries the code

20. The DNA Code & Protein Synthesis
So, the big question is…
How does the DNA code in a cell’s nucleus get to the ribosomes where proteins are synthesized?
transcription & translation
Transcription & translation
The Central Dogma is: DNA -> RNA -> Protein
Or DNA is transcribed to RNA which is translated to protein. Protein is never back-translated to RNA or DNA; and except for retroviruses, DNA is never created from RNA. Furthermore, DNA is never directly translated to protein. DNA to RNA to protein

22. Transcription What is transcription? When does transcription happen?
DNA code is “transcribed”/copied into mRNA codons
When does transcription happen?
when a protein is needed
Where does transcription happen?
in the nucleus
When a protein is needed, the region of DNA near the necessary gene gives the signal “start codon”
DNA unzips (only at needed section)
Complementary RNA nucleotides from cytoplasm line up until reaching a “stop codon” (with help of RNA polymerase)
Nucleotides bond to form single RNA strand of mRNA (messenger RNA)
The 2 DNA strands rejoin & mRNA moves out of nucleus into cytoplasm
Codon (triplet code) – 3 consecutive bases that code for an amino acid… 64 possible combinations… So, some amino acids have more than one codon

23. Transcription What does transcription make?
What does transcription make?
A single-stranded messenger RNA (mRNA)
made from instructions/order of the bases in the DNA
When a protein is needed, the region of DNA near the necessary gene gives the signal “start codon”
DNA unzips (only at needed section)
Complementary RNA nucleotides from cytoplasm line up until reaching a “stop codon” (with help of RNA polymerase)
Nucleotides bond to form single RNA strand of mRNA (messenger RNA)
The 2 DNA strands rejoin & mRNA moves out of nucleus into cytoplasm
Codon (triplet code) – 3 consecutive bases that code for an amino acid… 64 possible combinations… So, some amino acids have more than one codon

24. Transcription What are the steps in transcription? DNA unzips
What are the steps in transcription?
DNA unzips
free RNA nucleotides pair w/ exposed bases on DNA
until “stop codon” is reached
mRNA separates from DNA
& moves out of nucleus
to ribosome in cytoplasm
DNA strands rejoin
When a protein is needed, the region of DNA near the necessary gene gives the signal “start codon”
DNA unzips (only at needed section)
Complementary RNA nucleotides from cytoplasm line up until reaching a “stop codon” (with help of RNA polymerase)
Nucleotides bond to form single RNA strand of mRNA (messenger RNA)
The 2 DNA strands rejoin & mRNA moves out of nucleus into cytoplasm
Codon (triplet code) – 3 consecutive bases that code for an amino acid… 64 possible combinations… So, some amino acids have more than one codon

25. mRNA Carries DNA’s Code Using “Codons”
What is a codon?
3 consecutive bases on mRNA that codes for a particular amino acid
64 possible combos
Some amino acids have more than one codon
Codon (triplet code) – 3 consecutive bases that code for an amino acid… 64 possible combinations… So, some amino acids have more than one codon
20 different amino acids, but DNA contains only 4 kinds of bases
DNA “language” is converted to protein language in the cytoplasm
Codons are read only in one direction
DNA code is a universal one (w/ rare exceptions) a codon representing a given amino acid in one organism represents the same amino acid in another organism
DNA code must have arisen very early in the evolution of life & then been passed down unaltered to all later life forms Replication ensures that exact copes of DNA were made & passed on, unaltered, to offspring
Codon (triplet code) – 3 consecutive bases that code for an amino acid… 64 possible combinations… So, some amino acids have more than one codon AUG = start codon (met a.a.) UAA, UAG, UGA = stop codons

26. mRNA Carries DNA’s Code Using “Codons”
How can we figure out the amino acid coded for by a codon?
a codon chart
Codon (triplet code) – 3 consecutive bases that code for an amino acid… 64 possible combinations… So, some amino acids have more than one codon
Codons are read only in one direction
DNA code is a universal one (w/ rare exceptions) a codon representing a given amino acid in one organism represents the same amino acid in another organism
DNA code must have arisen very early in the evolution of life & then been passed down unaltered to all later life forms Replication ensures that exact copes of DNA were made & passed on, unaltered, to offspring
Codon (triplet code) – 3 consecutive bases that code for an amino acid… 64 possible combinations… So, some amino acids have more than one codon AUG = start codon (met a.a.) UAA, UAG, UGA = stop codons
What amino acid does the AUG codon code for?

28. mRNA Codons & Amino Acids
What amino acid does the AUG codon code for?
It must be in this row
Codons are read only in one direction
DNA code is a universal one (w/ rare exceptions) a codon representing a given amino acid in one organism represents the same amino acid in another organism
DNA code must have arisen very early in the evolution of life & then been passed down unaltered to all later life forms Replication ensures that exact copes of DNA were made & passed on, unaltered, to offspring
Codon (triplet code) – 3 consecutive bases that code for an amino acid… 64 possible combinations… So, some amino acids have more than one codon AUG = start codon (met a.a.) UAA, UAG, UGA = stop codons
It must be in this square
It must be in this amino acid

29. mRNA Codons & Amino Acids
Codons are read only in one direction
DNA code is a universal one (w/ rare exceptions) a codon representing a given amino acid in one organism represents the same amino acid in another organism
DNA code must have arisen very early in the evolution of life & then been passed down unaltered to all later life forms Replication ensures that exact copes of DNA were made & passed on, unaltered, to offspring
Codon (triplet code) – 3 consecutive bases that code for an amino acid… 64 possible combinations… So, some amino acids have more than one codon AUG = start codon (met a.a.) UAA, UAG, UGA = stop codons

30. Translation What is translation? When does translation occur?
process of reading mRNA codons to synthesize proteins
with help of tRNA (transfer RNA) & ribosomes
When does translation occur?
when mRNA from the nucleus joins with ribosomes
Where does translation happen?
at ribosomes in the cytoplasm
The cell “reads” the codons & links together certain amino acids using tRNA to form a particular protein
Anticodon (tRNA’s complementary bases to codon on mRNA)
Amino acid = monomer, polypeptide (protein) = polymer

31.
Steps of Translation
mRNA comes from the nucleus & joins with ribosome in cytoplasm
Ribosome “reads” the codon until it finds the start codon (AUG)
tRNA (with complementary anticodon) joins to the mRNA codon
tRNA carries the amino acid specified by the mRNA codon
The cell “reads” the codons & links together certain amino acids using tRNA to form a particular protein
Anticodon (tRNA’s complementary bases to codon on mRNA)
Amino acid = monomer, polypeptide (protein) = polymer

32.
Steps of Translation
Ribosome moves along mRNA reading each codon until “stop” codon is reached
tRNA brings each amino acid
Amino acids line up & bond to form polypeptide
Polypeptide chain forms protein (3-D)
Shape of protein is related to its function
The cell “reads” the codons & links together certain amino acids using tRNA to form a particular protein
Anticodon (tRNA’s complementary bases to codon on mRNA)
Amino acid = monomer, polypeptide (protein) = polymer

34. tRNA anticodon
DNA codon
mRNA codon
transcription
translation

37. Let’s Practice… What would the mRNA strand made during transcription look like?
UGG UUU GGC UCA

38. What amino acids would be coded for using this mRNA?
Trp Phe Gly Ser

39. What would the anticodons on the tRNA be for each amino acid?
ACC AAA CCG AGU

40. Let’s Practice… Given the DNA sequence below, determine the:
mRNA codon sequence
amino acids that would be coded for by each codon
anticodons on each tRNA which allowed it to “bring” that amino acid (using the mRNA codons)
DNA = TAC CCA TTG GAT CCG ACT
mRNA codon =
amino acid =
tRNA anticodon =
DNA = TAC CCA TTG GAT CCG ACT
mRNA = AUG GGU AAC CUA GGC UGA
A. A. = Met/start Gly Asn Leu Gly stop
Anticodon = UAC CCA UUG GAU CCG ACU
AUG GGU AAC CUA GGC UGA
Met/start Gly Asn Leu Gly stop
UAC CCA UUG GAU CCG ACU

41. Mutations What are mutations?
mistakes/changes in a gene on a chromosome
can occur spontaneously during replication
can be caused by mutagens (such as radiation, high temperatures, or chemicals)
often corrected, but not always
once occurs, copied as if correct
can cause different protein
Replication of DNA is usually accurate, however mistakes can occur
Mutagens can break bonds or cause unusual bonds in DNA… Some mutagens known to play role in development of many forms of cancer ex. UV & skin cancer

42. Types of Mutations What are the 3 types of mutations? deletion
What happens in a deletion mutation?
a nucleotide (base) is left out
causes “frame shift”
~moves nucleotides after the deletion to the left causing a
different protein to be formed
Picture: top box = mRNA codon & bottom box = protein produced…. Top pair of boxes = normal & bottom pair of boxes = w/ mutation
Both cause “frame shift” (Shift the reading of DNA message over by one nucleotide)… Causes a different amino acid sequence from that point on… Results in synthesis of a different polypeptide (b/c changes translation)… polypeptide produced, if one produced at all, is usually not functional
Usually most serious type

43. Types of Mutations insertion What happens in an insertion mutation?
a nucleotide (base) is added in
causes “frame shift”
~moves nucleotides after the insertion to the right causing a
different protein to be formed
Picture: top box = mRNA codon & bottom box = protein produced…. Top pair of boxes = normal & bottom pair of boxes = w/ mutation
Both cause “frame shift” (Shift the reading of DNA message over by one nucleotide)… Causes a different amino acid sequence from that point on… Results in synthesis of a different polypeptide (b/c changes translation)… polypeptide produced, if one produced at all, is usually not functional
Usually most serious type

44. Types of Mutations point (base substitution)
What happens in a point mutation?
one nucleotide (base) is replaced by another
affects only 1 amino acid & does not cause “frame shift”
sometimes amino acid & protein can be the same (“silent mutation”)
protein may be able to function normally or nearly normally
Affects only 1 amino acid in the polypeptide… The polypeptide may be able to function normally or nearly normally
Usually not too serious

45. Sickle Cell Mutation What does the sickle cell mutation do?
affects hemoglobin
What type of mutation causes sickle cell?
A point mutation
changes one amino acid
changes the protein
hemoglobin (protein in blood which carries oxygen)

46. “Silent” mutation (no change in polypeptide)
(point mutation)
Silent mutations show no effect b/c still getting same polypeptide  upper right hand base-pair sub