1. Nucleic Acids

2. DNA or Protein?
Walter Sutton discovered chromosomes were made of DNA and Protein
However, scientists were NOT sure which one (protein or DNA) was the actual genetic material of the cell

3. DNA!
Frederick Griffith in 1928 showed the DNA was the cell’s genetic material
Watson & Crick in the 1950’s built the 1st model of DNA

4. Structure of DNA DNA is made of subunits called nucleotides
DNA nucleotides are composed of a phosphate, deoxyribose sugar, and a nitrogen-containing base
The 4 bases in DNA are: adenine (A), thymine (T), guanine (G), and cytosine (C)

5. Notice that the 3’ and 5’ refer to a numbering system for the carbon atoms that make up the sugar.
DNA Nucleotide

6. Base Pairing Rule
Watson and Crick showed that DNA is a double helix w/ Chargaff’s rule
A (adenine) pairs with T (thymine)
C (cytosine) pairs with G (guanine)

7. Nitrogen Rings Purines have double rings of carbon-nitrogen (G, A)
Pyrimidines have single carbon-nitrogen rings (C, T)
This is called complementary base pairing because a purine is always paired with a pyrimidine

8. 5’ to 3’ Sugars .
When the DNA double helix unwinds, it resembles a ladder
The sides of the ladder are the sugar-phosphate backbones
The rungs of the ladder are the complementary paired bases
The two DNA strands are anti-parallel (they run in opposite directions)

9. Replication Facts DNA has to be copied before a cell divides
DNA is copied during the S or synthesis phase of interphase
New cells will need identical DNA strands

10. Synthesis Phase (S phase)
S phase during interphase of the cell cycle
Nucleus of eukaryotes
Mitosis
-prophase
-metaphase
-anaphase
-telophase G1 G2 S
phase
interphase
DNA replication takes
place in the S phase.

11. DNA  RNA  Protein Prokaryotic Cell DNA mRNA Ribosome Protein
Transcription
Translation
DNA
mRNA
Ribosome
Protein
Prokaryotic Cell

12. DNA
pre-mRNA
RNA Polymerase

13. Steps in DNA Replication
Occurs when chromosomes duplicate (make copies)
Enzyme DNA Helicase unwinds & separates the 2 DNA strands by breaking the weak
hydrogen bonds as enzymes “unzip” the molecule
Each old strand of nucleotides serves as a template for each new strand
New nucleotides move into complementary positions are joined by DNA polymerase
DNA polymerase is an enzyme.

14. DNA Replication

15. Anti-Parallel Strands of DNA
On the left is the DNA double helix. When the helix is unwound, a ladder configuration shows that the uprights are composed of sugar and phosphate molecules and the rungs are complementary bases. Notice that the bases in DNA pair in such a way that the phosphate-sugar groups are oriented in different directions. This means that the strands of DNA end up running antiparallel to one another, with the 3’ end of one strand opposite the 5’ end of the other strand.

16. DNA Replication Begins at Origins of Replication
One strand serves as a mold for another strand to be copied
Two strands open forming Replication Forks (Y-shaped region)
New strands grow at the forks
Replication
Fork
Parental DNA Molecule 3’ 5’

17. Two New, Identical DNA Strands Result from Replication
Replication is called semiconservative because each new double helix is composed of an old (parental) strand and a new (daughter) strand.

18. Another View of Replication
Use of the ladder configuration better illustrates how complementary nucleotides available in the cell pair with those of each old strand before they are joined together to form a daughter strand.

19. PROTEIN SYNTHESIS

20. Protein Synthesis
The production (synthesis) of polypeptide chains (proteins)
Two phases: Transcription & Translation
mRNA must be processed before it leaves the nucleus of eukaryotic cells

21. Two Parts of Protein Synthesis
Transcription makes an RNA molecule complementary to a portion of DNA
Translation occurs when the sequence of bases of mRNA DIRECTS the sequence of amino acids in a polypeptide

22. .
Three Types of RNA
Messenger RNA (mRNA) carries genetic information to the ribosomes
Ribosomal RNA (rRNA), along with protein, makes up the ribosomes
Transfer RNA (tRNA) transfers amino acids to the ribosomes where proteins are synthesized

23. Pathway to Making a Protein
DNA
mRNA
tRNA (ribosomes)
rRNA - Protein

24. DNA  RNA  Protein Eukaryotic Cell DNA Pre-mRNA mRNA Ribosome Protein
Nuclear
membrane
Transcription
RNA Processing
Translation
DNA
Pre-mRNA
mRNA
Ribosome
Protein
Eukaryotic Cell

25. DNA
pre-mRNA
RNA Polymerase

26. RNA

27. RNA Differs from DNA DNA has a sugar deoxyribose
1. RNA has a sugar ribose
DNA has a sugar deoxyribose
2. RNA contains the base uracil (U)
DNA has thymine (T)
3. RNA molecule is single-stranded
DNA is double-stranded

28. Structure of RNA
Like DNA, RNA is a polymer of nucleotides. In an RNA nucleotide, the sugar ribose is attached to a phosphate molecule and to a base, either G, U, A, or C. Notice that in RNA, the base uracil replaces thymine as one of the pyrimidine bases. RNA is single-stranded, whereas DNA is double-stranded.

29. Messenger RNA Long Straight chain of Nucleotides Made in the Nucleus
Copies DNA & leaves through nuclear pores
Contains the Nitrogen Bases
G, C, A, U ( no T )

30. Code for making a Protein

31. Transcription

32. Steps in Transcription
The transfer of information in the nucleus from a DNA molecule to an RNA molecule
Only 1 DNA strand serves as the template
Starts at promoter DNA (TAC box)
Ends at terminator DNA (stop)
When complete, m-RNA molecule is released

33. RNA Polymerase Enzyme found in the nucleus
Separates the two DNA strands by breaking the hydrogen bonds between the bases
Then moves along one of the DNA strands and links RNA nucleotides together

34. Overview of Transcription
During transcription in the nucleus, a segment of DNA unwinds and unzips, and the DNA serves as a template for mRNA formation
RNA polymerase joins the RNA nucleotides so that the codons in mRNA are complementary to the triplet code in DNA

35. During transcription, complementary RNA is made from a DNA template
During transcription, complementary RNA is made from a DNA template. A portion of DNA unwinds and unzips at the point of attachment of RNA polymerase. A strand of mRNA is produced when complementary bases join in the order dictated by the sequence of bases in DNA. Transcription occurs in the nucleus, and the mRNA passes out of the nucleus to enter the cytoplasm.

36. RNA Polymerase

37. mRNA Transcript
mRNA leaves the nucleus through its pores and goes to the ribosomes

38. G Transcription C Translation amino acids threonine
Transcription occurs when DNA acts as a template for mRNA synthesis. Translation occurs when the sequence of the mRNA codons determines the sequence of amino acids in a protein.
Translation
amino acids
threonine

40. Genes & Proteins
Proteins are made of amino acids linked together by peptide bonds
20 different amino acids exist
Amino acids chains are called polypeptides
Segment of DNA that codes for the amino acid sequence in a protein are called genes

41. Amino Acid Structure

42. Genetic Code DNA contains a triplet code
Every three bases on DNA stands for ONE amino acid
Each three-letter unit on mRNA is called a codon
Most amino acids have more than one codon!
There are 20 amino acids with a possible 64 different triplets
The code is nearly universal among living organisms
The fact that the genetic code is about universal in living things suggests that the code dates back to the first organisms on earth and that all living things are related.

43. The Genetic Code
Use the code by reading from the center to the outside
Example: AUG codes for Methionine

44. 1. Use base pair rule to complement
this strand of DNA.
____________________
G A T T A C A G C
l l l l l l l l l
2. Use top strand of DNA to
transcribe mRNA codon strand.
3. Use mRNA codon charts to
determine amino acid sequence.

45. Practice deciphering amino acid
Sequence from … mRNA …
… DNA and …. amino acid
Use “Skill and Challenge” charts

46. Notice that in this chart, each of the codons (white rectangles) is composed of three letters representing the first base, second base, and third base. For example, find the rectangle where C for the first base and A for the second base intersect. You will see that U, C, A, or G can be the third base. CAU and CAC are codons for histidine; CAA and CAG are codons for glutamine.

47. Translation Synthesis of proteins in the cytoplasm
Involves the following:
1. mRNA (codons)
2. tRNA (anticodons)
3. rRNA ribosomes
4. amino acids

48. Messenger RNA (mRNA) Primary structure of a protein A U G C aa1 aa2
DNA : T A C C C G A G G T A G C C G C G T A T T A U G C
mRNA
start
codon
codon 2
codon 3
codon 4
codon 5
codon 6
codon 7
codon 1
methionine
glycine
serine
isoleucine
alanine
stop
codon
protein
Primary structure of a protein
aa1
aa2
aa3
aa4
aa5
aa6
peptide bonds

49. .
Three Types of RNA
Messenger RNA (mRNA) carries genetic information to the ribosomes
Ribosomal RNA (rRNA), along with protein, makes up the ribosomes
Transfer RNA (tRNA) transfers amino acids to the ribosomes where proteins are synthesized

50. DNA - TAC GCA ATT CGC ATC mRNA rRNA tRNA tRNA codon anticodon

51. A U G C AA T A C C C G A G G T A G C C G C G T A T T DNA start codon
mRNA
start
codon
tRNA
anticodon AA
MET

52. Notice that in this chart, each of the codons (white rectangles) is composed of three letters representing the first base, second base, and third base. For example, find the rectangle where C for the first base and A for the second base intersect. You will see that U, C, A, or G can be the third base. CAU and CAC are codons for histidine; CAA and CAG are codons for glutamine.

53. What is the enzyme responsible for the production of the mRNA molecule?

54. Question:
What would be the complementary RNA strand for the following DNA sequence?
DNA 5’-GCGTATG-3’

55. Answer:
DNA 5’-GCGTATG-3’
RNA 3’-CGCAUAC-5’

56. PROTEIN SYNTHESIS

57. Protein Synthesis
The production (synthesis) of polypeptide chains (proteins)
Two phases: Transcription & Translation
mRNA must be processed before it leaves the nucleus of eukaryotic cells

58. DNA makes proteins that are needed
for growth, repair and all life functions
Ex:
collagen - cartilage and tendons
hemoglobin – blood carries oxygen
through the body
keratin - hair and fingernails
insulin – metabolizes blood sugars
…muscles, skin, etc…

59. mRNA Processing
After the DNA is transcribed into RNA, editing must be done to the nucleotide chain to make the RNA functional
Introns, non-functional segments of DNA are snipped out of the chain

60. Processing -mRNA Also occurs in the nucleus
mRNA made up of segments called introns & exons
Exons code for proteins, while introns do NOT!
Introns spliced out by splicesome-enzyme and exons re-join
End product is a mature mRNA molecule that leaves the nucleus to the cytoplasm / then ribosome

61. RNA Processing mRNA molecule Mature RNA molecule intron exon exon exon
splicesome
exon
Mature RNA molecule

62. mRNA Editing
Exons, segments of DNA that code for proteins, are then rejoined by the enzyme ligase
A guanine triphosphate cap is added to the 5” end of the newly copied mRNA
A poly A tail is added to the 3’ end of the RNA
The newly processed mRNA can then leave the nucleus

63. Result of Transcription
New Transcript
Tail
CAP

64. Messenger RNA (mRNA) Carries the information for a specific protein
Made up of 500 to 1000 nucleotides long
Sequence of 3 bases called codon
AUG – methionine or start codon
UAA, UAG, or UGA – stop codons

65. Codons and Anticodons
The 3 bases of an anticodon are complementary to the 3 bases of a codon
Example: Codon ACU
Anticodon UGA
UGA
ACU

66. Translation Synthesis of proteins in the cytoplasm
Involves the following:
1. mRNA (codons)
2. tRNA (anticodons)
3. rRNA ribosomes
4. amino acids

67. Translation
Translation is the process of decoding the mRNA into a polypeptide chain
Ribosomes read mRNA three bases or 1 codon at a time and construct the proteins

68. A U G C AA T A C C C G A G G T A G C C G C G T A T T DNA start codon
mRNA
start
codon
tRNA
anticodon AA
MET

69. Transfer RNA (tRNA) Made up of 75 to 80 nucleotides long
Picks up the appropriate amino acid floating in the cytoplasm
Transports amino acids to the mRNA
Have anticodons that are complementary to mRNA codons
Recognizes the appropriate codons on the mRNA and bonds to them with H-bonds

70. Transfer RNA (tRNA) methionine amino acid attachment site amino acidU A C
anticodon
methionine
amino acid

71. Translation Let’s Make a Protein ! Three steps:
1. initiation: start codon (AUG)
2. elongation: amino acids linked
3. termination: stop codon (UAG, UAA, or UGA).
Let’s Make a Protein !

72. Step 1- Initiation
mRNA transcript start codon AUG attaches to the small ribosomal subunit
Small subunit attaches to large ribosomal subunit
mRNA transcript

73. Step 2 - Elongation
As ribosome moves, two tRNA with their amino acids move into site A and P of the ribosome
Peptide bonds join the amino acids

74. Ribosomal RNA (rRNA) Made up of rRNA is 100 to 3000 nucleotides long
Made inside the nucleus of a cell
Associates with proteins to form ribosomes

75. Ribosomes Made of a large and small subunit
Composed of rRNA (40%) and proteins (60%)
Have two sites for tRNA attachment --- P and A

76. Ribosomes
Large
subunit P
Site A
Site
mRNA A U G C
Small subunit

77. mRNA Codons Join the Ribosome
Large
subunit P
Site A
Site
mRNA A U G C
Small subunit

78. Initiation G aa2 A U U A C aa1 A U G C U A C U U C G A codon 2-tRNA
anticodon A U G C U A C U U C G A
hydrogen
bonds
codon
mRNA

79. Elongation G A aa3 peptide bond aa1 aa2 U A C G A U A U G C U A C U U
3-tRNA G A
aa3
peptide bond
aa1
aa2
1-tRNA
2-tRNA
anticodon U A C G A U A U G C U A C U U C G A
hydrogen
bonds
codon
mRNA

80. Ribosomes move over one codon
aa1
peptide bond
3-tRNA G A
aa3
aa2
1-tRNA U A C
(leaves)
2-tRNA G A U A U G C U A C U U C G A
mRNA
Ribosomes move over one codon

81. peptide bonds G C U aa4 aa1 aa2 aa3 G A U G A A A U G C U A C U U C G
4-tRNA G C U
aa4
aa1
aa2
aa3
2-tRNA
3-tRNA G A U G A A A U G C U A C U U C G A A C U
mRNA

82. Ribosomes move over one codon
peptide bonds
4-tRNA G C U
aa4
aa1
aa2
aa3
2-tRNA G A U
(leaves)
3-tRNA G A A A U G C U A C U U C G A A C U
mRNA
Ribosomes move over one codon

83. peptide bonds U G A aa5 aa1 aa2 aa4 aa3 G A A G C U G C U A C U U C G
5-tRNA
aa5
aa1
aa2
aa4
aa3
3-tRNA
4-tRNA G A A G C U G C U A C U U C G A A C U
mRNA

84. Ribosomes move over one codon
peptide bonds U G A
5-tRNA
aa5
aa1
aa2
aa3
aa4
3-tRNA G A A
4-tRNA G C U G C U A C U U C G A A C U
mRNA
Ribosomes move over one codon

85. Termination aa5 aa4 aa3 primary structure of a protein aa2 aa1 A C U C
terminator
or stop
codon
200-tRNA A C U C A U G U U U A G
mRNA

86. End Product –The Protein!
The end products of protein synthesis is a primary structure of a protein
A sequence of amino acid bonded together by peptide bonds
aa1
aa2
aa3
aa4
aa5
aa200
aa199