1. Transcription and Translation

2. Central Dogma Central Dogma: DNA  RNA  protein
Transcription: DNA  RNA
Translation: RNA  protein
Ribosome = site of translation
one gene-one protein hypothesis
RNA can then be translated into a polypeptide

3. A gene is a segment of DNA that encodes a protein
Genes vary in size, from just a few thousand pairs of nucleotides to over 2 million!
You have about 6 billion nucleotides in each of your cells. This means in your DNA there is roughly 30,000 genes!

4. The DNA genetic codes are expressed as proteins, which provide molecular basis for physical traits
Genotype: genetic makeup.
Heritable information contained in its DNA
Phenotype: organism’s specific traits
Physically what you can see.

5. The Lesser Known Nucleic Acid
DNA
RNA is the intermediate between DNA and proteins
RNA is a single stranded nucleic acid
TRANSCRIPTION
mRNA
TRANSLATION
Protein

6. RNA Nucleotide Structure
Sugar
Ribose
Phosphate Group
Nitrogenous Base
Adenine (A)
Cytosine (C)
Guanine (G)
Uracil (U)
Nitrogenous base (A, G, C, or U)
Phosphate group
Difference in structure, sugar, and nucleotides between RNA and DNA
Sugar (ribose)

7. Types of RNA Messenger RNA (mRNA)
Carries instructions from DNA to ribosome
Ribosomal RNA (rRNA)
Combines with proteins to make up ribosomes
Transfer RNA (tRNA)
Bind specific amino acids and allow information in the mRNA to be translated into a linear peptide sequence

8. DNA vs. RNA

9. mRNA Messenger RNA Function: mRNA is read as triplets of codons
Carry genetic information between the nucleus and cytoplasm
mRNA is read as triplets of codons
The codons in a gene specify the amino acid sequence of a polypeptide
Single stranded and complementary to DNA
Amino acid
Amino acid

10. TRANSCRIPTION TRANSLATION Gene 1 Gene 3 DNA molecule Gene 2 DNA strand
mRNA
Codon
TRANSLATION
Polypeptide
(a protein)
Amino acid

11. Example Problem:
A particular protein is 100 amino acids long. In the gene for this protein, how many nucleotides are necessary to code for this protein?
1 amino acid = 1 codon
100 amino acids = 100 codons
1 codon = 3 nucleotides
100 x 3 = 300!
300

12. Transcription: transfer of genetic information from DNA  RNA
Occurs in the cell nucleus
DNA strands separate via helicase
(only 1 serves as template)
Nucleotides making up new RNA molecule take their place forming hydrogen bonds w/ DNA bases
U pairs with A instead of T
RNA nucleotides linked by enzyme
RNA polymerase

13. Transcription RNA polymerase RNA nucleotide Direction of transcription
Template strand of DNA
Newly made RNA

14. RNA polymerase
Initiation: promoter located at beginning of gene, starts transcribing signal
Elongation: As RNA synthesis continues, the RNA strand peels away from the DNA. DNA strands come back together
Termination: RNA polymerase reaches a special sequence of bases in the DNA template called the terminator.
DNA of gene
Promoter
DNA
Terminator
DNA
Initiation
Elongation
Promoter dictates which of the two DNA strands is to be transcribed
After Termination, the polymerase molecule detaches from RNA and gene.
Termination
Growing mRNA
Completed mRNA
RNA polymerase

15. 1. Initiation of Transcription
Transcription factors bind to the promoter on DNA and attract RNA polymerase to begin transcription.
Promoter dictates which of the two DNA strands is to be transcribed. Provides the location for the start of transcription.

16. 2. Elongation mRNA strand grown in 5’  3’ direction by RNA polymerase
DNA is read in a 3’ to 5’ direction
As RNA polymerase moves, it untwists DNA, then rewinds it after mRNA is made

17. RNA polymerase
Termination: RNA polymerase reaches a special sequence of bases in the DNA template called the terminator.
DNA of gene
Promoter
DNA
Terminator
DNA
Initiation
Elongation
Promoter dictates which of the two DNA strands is to be transcribed. Provides the location for the start of transcription.
After Termination, the polymerase molecule detaches from RNA and gene.
Termination
Growing mRNA
Completed mRNA
RNA polymerase
Transcription Video

18. mRNA transcript undergoes a series of enzyme regulated modifications
DNA
RNA transcript with cap and tail
mRNA
Exon
Intron
Transcription Addition of cap and tail
Introns removed
Exons spliced together
Coding sequence
NUCLEUS
CYTOPLASM
Tail
Cap
mRNA molecule contains both exons and introns
Exon- region of gene that codes for a protein
Intron- noncoding region within a gene

19. Alternate Splicing
Alternate splicing of one gene can form different proteins in eukaryotes
30,000 genes  100,000 possible polypeptides

20. Occurs in the Cytoplasm
TRANSLATION
Occurs in the Cytoplasm

21. TRANSLATION TRANSCRIPTION Gene 1 Gene 3 DNA molecule Gene 2 DNA strand
mRNA
Codon
TRANSLATION
Polypeptide
(a protein)
Amino acid

22. Dictionary of the genetic code (RNA codons)
61 of the 64 triplets code for amino acids
AUG = Met and provides the start signal
UAA, UAG, UGA = stop codons. Instruct ribosomes to end the polypeptide

23. CODON CHART

24. Example Problems: Translate the mRNA sequence
CCAUUUACG
What is the polypeptide sequence for the following DNA strand?
TACTTCAAAATC
Pro-Phe-Thr
Met- Lys- Phe, stop!

25. Transcribed strand
DNA
Transcription
mRNA
Start codon
Stop codon
Translation
Polypeptide

26. Components of Translation
mRNA = message
tRNA = interpreter
Ribosome = site of translation

27. tRNA: transfer RNA Serves as interpreter during translation
Amino acid attachment site
Serves as interpreter during translation
Converts 3-letter codons into amino acid words
GCUAlanine (Ala)
In the cytoplasm, a ribosome attaches to the mRNA and translates its message into a polypeptide
Process aided by tRNA
Hydrogen bond
A cell that is ready to carry out translation has its cytoplasm full of amino acids, obtained from food or made from other chemicals
tRNA structure
Made of a single strand of RNA
Folded and twisted at one end of the folded molecule contains a special triplet of bases = anticodon
the anticodon is complementary to a codon triplet on mRNA
The anticodon on tRNA recognizes a particular codon on mRNA and at the end of the tRNA, an amino acid attaches
Enzymes attach amino acid and tRNA in cytoplasm with ATP energy
RNA polynucleotide chain
Anticodon

28. tRNA
Amino acids cannot recognize codons of mRNA, they need tRNA to match amino acids to the correct codon
Carries out 2 functions
At one end, it picks up the appropriate amino acid with help of enzyme and ATP
The anticodon recognizes a particular codon on mRNA
the anticodon is complementary to a codon triplet on mRNA
The anticodon on tRNA recognizes a particular codon on mRNA and at the end of the tRNA, an amino acid attaches

29. Ribosomes build polypeptides
rRNA + proteins
Active Sites
A site- holds amino acid to be added
P site- holds growing polypeptide chain
E site- exit site for tRNA

30. Ribosomes build polypeptides
Ribosomes consist of 2 subunits
Small subunit: binding site for mRNA
Large subunit: binding site for tRNA
Next amino acid to be added to polypeptide
P site
A site
Growing polypeptide
Subunits of ribosomes: made up of proteins and ribosomal RNA (rRNA)
Large subunit
P-site holds the tRNA carrying the growing polypeptide chain
A-site holds the tRNA carrying the next amino acid to be added
Large subunit
tRNA
mRNA
mRNA binding site
Codons
small subunit

31. Translation: initiation, elongation, termination
mRNA binds to small ribosomal subunit.
tRNA bonds to start codon.
Large ribosomal subunit binds to small one.
Initiator tRNA fits into P-site.
Initiator tRNA carries amino acid methionine (Met), its anticodon UAC binds to AUG.
When large ribosomal subunit binds to small one = functional ribosome.
Codon recognition: the anticodon of incoming tRNA carrying its amino acid pairs with the mRNA codon in the A site of the ribosome.
Peptide bond formation: polypeptide separates from tRNA in the p-site and attaches by peptide bond to the amino acid in the A-site.
Translocation: tRNA in the P-site leaves ribosome and ribosome translocates (moves) the tRNA in the A-site to the P-site. Codon and anticodon remain onded and the movement drags the next codon into the A-site.

32. 2. Elongation

33. 2. Elongation
Codon recognition: tRNA anticodon matches codon in A site

34. 2. Elongation
Peptide bond formation: Peptide in P site forms bond with AA in A site

35. 2. Elongation
Translocation: tRNA in A site moves to P site; tRNA in P site moves to E site (then exits)

36. 2. Elongation
Repeat over and over

37. Elongation continues until?
Elongation continues until the stop codon reaches the A-site.
Stop codons
UAA
UAG
UGA
=TERMINATION STAGE
Ribosomal subunits breakdown
Translation Video

38. Review DNA RNA Protein
Transcription
(DNARNA)
Occurs in nucleus, mRNA travels to cytoplasm
Translation
tRNAs add their amino acids to the polypeptide chain as the mRNA is moved through the ribosome one codon at a time.
Ribosome recognizes a stop codon. Polypeptide chain is terminated and released.

39. Summary of transcription & translation
DNA
Stage mRNA is transcribed from a DNA template. 1
mRNA
RNA polymerase
Amino acid
TRANSLATION
Stage Each amino acid attaches to its proper tRNA with the help of a specific enzyme and ATP. 2
Enzyme
tRNA
Initiator
tRNA
Anticodon
Stage Initiation of polypeptide synthesis 3
Large ribosomal subunit
The mRNA, the first tRNA, and the ribosomal subunits come together.
Start Codon
Small ribosomal subunit
mRNA

40. New peptide bond forming
Growing
polypeptide
Stage Elongation 4
A succession of tRNAs add their amino acids to the polypeptide chain as the mRNA is moved through the ribosome, one codon at a time.
Codons
mRNA
Polypeptide
Stage Termination 5
The ribosome recognizes a stop codon. The poly-peptide is terminated and released.
Stop
Codon

41. Protein Packaging and Secretion

42. Mutations Changes in the nucleotide sequence of DNA
that are passed on from cell to cell
Mutations can cause loss-of-function

43. Mutations = changes in the genetic material of a cell
Large scale mutations: chromosomal; always cause disorders or death
Deletion- loss of chromsome segment
Duplication- homologous chromosomes break at different locations and swap DNA, one chromosome will gain DN, the other will lose
Inversion- piece of DNA breaks off and reinserted in the wrong orientation
Translocation- DNA segments break off and join to non-homologous chromosome

44. Mutations Activity Point mutations: alter 1 base pair of a gene
Base-pair substitutions – replace 1 with another
Missense: different amino acid
Nonsense: stop codon, not amino acid
Silent: no change in amino acid
Frameshift – mRNA read incorrectly; nonfunctional proteins
Caused by insertions or deletions

45. Mutations Overview Chromosomal mutations Point mutations
Change in chromosomes structure
Results in changes to position or orientation of genes
Point mutations
Results from gain, loss or substitution of one nucleotide
Results in new alleles

46. Example: Sickle Cell Disease Pulmonary hypertension
Symptoms
Anemia
Pain
Frequent infections
Delayed growth
Stroke
Pulmonary hypertension
Organ damage
Blindness
Jaundice
gallstones
Caused by a genetic defect
Carried by 5% of humans
Carried by up to 25% in some regions of Africa
Life expectancy
42 in males 48 in females

47. Sickle-Cell Disease = Point Mutation
Mutation occurs in the beta chain – have them look at their amino acid structures and think about why the change may be important