1. Bell ringer:
Describe what is occurring with each of the following mutations
Frameshift
Deletion
Substitution
What is the name of the enzyme that makes telomeres?
In what direction is DNA replicated?
What is the function of RNA primase?

2. RNA vs. DNA structure

3. Types of RNA RNA is a polymer of RNA nucleotides
RNA Nucleotides are of four types: Uracil, Adenine, Cytosine, and Guanine
Uracil (U) replaces thymine (T) of DNA
Types of RNA
Messenger (mRNA) - Takes genetic message from DNA in nucleus to ribosomes in cytoplasm
Ribosomal (rRNA) - Makes up ribosomes which read the message in mRNA
Transfer (tRNA) - Transfers appropriate amino acid to ribosome when “instructed”

4. DNA Repair Errors occur 1/10 billion nucleotides Mismatch repair
(Humans have 3 billion base pairs in their DNA)
Mismatch repair
DNA polymerase (yes…it’s 3rd function)
“Proofread” new DNA
Like the “delete” key on computer
Excision (“cut out”) repair
Nuclease

6. DNA Repair

7. Replication: Prokaryotic
Prokaryotic Replication
Bacteria have a single circular loop
Replication moves around the circular DNA molecule in both directions
Produces two identical circles
Cell divides between circles, as fast as every 20 minutes

8. Replication: Prokaryotic vs. Eukaryotic
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
origin
replication is
complete
replication is
occurring in
two directions
a. Replication in prokaryotes
replication fork
replication bubble
parental strand
new DNA
duplexes
b. Replication in eukaryotes
daughter strand

9. Protein Synthesis: Transcription & Translation
Unit 4: DNA
Chapter 13
DNA > mRNA > ribosome > protein

10. Protein Synthesis Overview
Two processes are required:
1. Transcription: DNA > mRNA
2. Translation: mRNA > protein

11. Transcription: DNA > mRNA
Process of making messenger RNA (mRNA) from a DNA template to take the DNA info outside of the nucleus

12. Bellringer Write the questions and answers
What is the difference between DNA and RNA in regards to structure and bases
What is the central dogma of molecular genetics?
What is the process of transcription?
List the three types of RNA

13. DNA can NOT leave the nucleus (too big)
Messenger RNA (mRNA) carries the info encoded in DNA out of the nucleus to the ribosomes located in the cytoplasm.

14. Steps of Transcription
1. DNA strands unwind & separate
2. DNA strand containing a specific gene serves as a template strand
3. RNA nucleotides are matched to complimentary DNA bases
4. mRNA molecule is complete and DNA rewinds

15. Bell Ringer (write the question)
What are the building blocks of proteins?
What enzyme relaxes the DNA strand?
Where is the replication fork assembled at? (hint where does DNA replication take place)
True/False prokaryotic DNA consist of telomeres

16. mRNA Processing
Introns: the mRNA contains extra info (junk) that must be removed (cut out)
Exons: the remaining pieces carry useful information are spliced (connected) together to make the complete mRNA

17. The bases of mRNA pair with DNA bases but RNA replaces T with U
DNA: C T G T A C G G A
---> Transcription
mRNA: G A C A U G C C U
DNA
RNA A U T G C
template strand

18. Check: Are there any T’s in your mRNA?
Now you try…
Based on the DNA template, create the matching mRNA strand:
DNA: C T A T G C A A A C T A T A G
mRNA: ______________________________
G A U A C G U U U G A U A U C
Check: Are there any T’s in your mRNA?
There shouldn’t be!!!

20. Translation: mRNA > protein
Process of making proteins from info on mRNA
mRNA travels out of nucleus to the ribosome, which “reads” the mRNA as a series of 3 letter words called codons

21. Bellringer Write the questions and answers
The process of converting Dna to Mrna is called?
The process of converting Mrna to a protein is called?
change this Dna molecule into Mrna
AATGCAATGGCCA
4. Where does transcription occur? where does translation?

22. Codon: 3-base code on mRNA that codes for a specific amino acid
Ex. CGU = alanine
GUU = valine
The sequence of bases in DNA tell mRNA what order amino acids must join together to make a particular protein.

23. Codons found in mRNA

24. Transfer RNA (tRNA) matches up with each codon and transfers the correct amino acid
Each tRNA molecule has 3 unpaired bases called the anticodon that is complementary to one mRNA codon.

25. Each amino acid is added to a growing chain of amino acids
Protein = peptide bonds connecting amino acids
Many different types of proteins exist because the number and sequence of amino acids can be different

26. Codons found in mRNA Practice translating mRNA into amino acids:
mRNA: AUG AAA AGU UGU CUG GUU UAA
A.A: ______________________________________
Met - Lys – Ser - Cys – Leu – Val - Stop

27. How DNA determines proteins
DNA molecules serve as templates for making messenger RNA molecules
Messenger RNA molecules move to ribosomes
Transfer RNA molecules bring amino acids to the ribosome
Polypeptides (proteins) are formed as ribosomes move along the messenger RNA strand

28. Gene Expression DNA in all of your body cells is the same!
Ex: DNA in your eye cells is the same DNA that is in your skin cells.
Different types of cells express different genes.
Ex: Your eyes may be green, while your skin is brown.
Specialization of cells is due to different patterns of gene expression, rather than different genes themselves.
Liver cells express different genes than blood cells

29. DNA: TAC TCC AGC GCA ACT
----Transcription---->
mRNA: AUG AGG UCG CGU UGA
----Translation--->
A.A.: met arg ser arg stop

30. Bell ringer What occurs in translation? What is the role of rRNA?
What is the role of tRNA?
Transfer RNA (tRNA) matches up with each codon and transfers the correct amino acid, the match is called _______

31. Mutations Mutations are heritable changes in genetic information.
Gene mutations
Points mutations: substitutions, insertions, deletions (also called frameshift mutations)

32. Mutations

33. Chromosomal Mutations
Deletion
Duplication
Inversion
translocation

34. Review Genetic Material DNA Structure DNA Replication Transcription
Transformation
DNA Structure
Watson and Crick
DNA Replication
Prokaryotic versus Eukaryotic
Replication Errors
Transcription
Translation
Structure of Eukaryotic Chromosome

35. Steps in Translation: Initiation
Components necessary for initiation are:
Small ribosomal subunit
mRNA transcript
Initiator tRNA, and
Large ribosomal subunit
Initiation factors (special proteins that bring the above together)
Initiator tRNA:
Always has the UAC anticodon
Always carries the amino acid methionine
Capable of binding to the P site

36. Steps in Translation: Initiation
Small ribosomal subunit attaches to mRNA transcript
Beginning of transcript always has the START codon (AUG)
Initiator tRNA (UAC) attaches to P site
Large ribosomal subunit joins the small subunit

37. Steps in Translation: Initiation
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
amino acid methionine
Met
initiator tRNA
E site
P site
A site
mRNA U A 5' A C U G 3'
Met
small ribosomal subunit
large ribosomal subunit U A C A U G 5' 3'
start codon
A small ribosomal subunit
binds to mRNA; an initiator
tRNA pairs with the mRNA
start codon AUG.
The large ribosomal subunit
completes the ribosome.
Initiator tRNA occupies the
P site. The A site is ready
for the next tRNA.
Initiation

38. Steps in Translation: Elongation
“Elongation” refers to the growth in length of the polypeptide
RNA molecules bring their amino acid fares to the ribosome
Ribosome reads a codon in the mRNA
Allows only one type of tRNA to bring its amino acid
Must have the anticodon complementary to the mRNA codon being read
Joins the ribosome at it’s A site
Methionine of initiator is connected to amino acid of 2nd tRNA by peptide bond

39. Steps in Translation: Elongation
Second tRNA moves to P site (translocation)
Spent initiator moves to E site and exits
Ribosome reads the next codon in the mRNA
Allows only one type of tRNA to bring its amino acid
Must have the anticodon complementary to the mRNA codon being read
Joins the ribosome at it’s A site
Dipeptide on 2nd amino acid is connected to amino acid of 3nd tRNA by peptide bond

40. Steps in Translation: Elongation
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Met
Met
asp
Met
peptide
bond
Met
tRNA
Ser
Ser
Thr
Ser
Ser
Ala
Ala
Ala C U G
Ala
Trp
peptide
bond
Trp U G G
Trp
anticodon
Trp
Val
Val
Val
Val
Asp
Asp
Asp A U C A U C A U C U G C U G C C A U C U G G U A G A C G U A G A C G U A G A C G U A G A C A C C 3 3 6 6 3 6 3 1
A tRNA–amino acid
approaches the
ribosome and binds
at the A site. 2
Two tRNAs can be at a
ribosome at one time;
the anticodons are
paired to the codons. 3
Peptide bond formation
attaches the peptide
chain to the newly
arrived amino acid. 4
The ribosome moves forward; the
“empty” tRNA exits from the E site;
the next amino acid–tRNA complex
is approaching the ribosome.
Elongation

41. Steps in Translation: Termination
Previous tRNA moves to P site
Spent tRNA moves to E site and exits
Ribosome reads the STOP codon at the end of the mRNA
UAA, UAG, or UGA
Does not code for an amino acid
Polypeptide is released from last tRNA by release factor
Ribosome releases mRNA and dissociates into subunits
mRNA read by another ribosome

42. Steps in Translation: Termination
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Asp
Ala
release factor
Trp
Asp
Val
Ala
Glu
Trp V al U U A A U G A
Glu 5'
stop codon 3'
The ribosome comes to a stop
codon on the mRNA. A release
factor binds to the site. U U C U G A A G A 3 5
The release factor hydrolyzes the bond
between the last tRNA at the P site and
the polypeptide, releasing them. The
ribosomal subunits dissociate.
Termination

43. Summary of Gene Expression (Eukaryotes)
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TRANSCRIPTION
TRANSLATION
1. DNA in nucleus serves
as a template for mRNA.
DNA
3. mRNA moves into
cytoplasm and
becomes associated
with ribosomes.
2. mRNA is processed
before leaving the nucleus.
mRNA
large and small
ribosomal subunits 5
pre-mRNA
introns 3'
mRNA
amino
acids
peptide
4. tRNAs with
anticodons carry
amino acids
to mRNA.
nuclear pore
ribosome
tRNA U A C U 5 G 3 A C A U
anticodon
codon
5. During initiation, anticodon-codon
complementary base pairing begins
as the ribosomal subunits come
together at a start codon. C
8. During termination, a
ribosome reaches a stop
codon; mRNA and
ribosomal subunits
disband. C C 5 C C C U G G U U U G G G A C C A A A G U A 3'
6. During elongation, polypeptide
synthesis takes place one
amino acid at a time.
7. Ribosome attaches to rough
ER. Polypeptide enters lumen,
where it folds and is
modified.

44. Structure of RNA P G G U S A P U base is uracil instead of thymine C S
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. P G G U S A P U
base is
uracil instead
of thymine C S P A S P C S
ribose
one nucleotide

45. Bell ringer What enzyme is responsible for making RNA strand?
What is the function of SSBP?
Describe the structure of DNA?
Provide an example of a Deletion mutation

46. Bell ringer: List the steps of transcription
True/false messanger RNA contains the nucleotide thymine
True/false DNA can leave the nucleus through nuclear pores
DNA is copied in what direction?