1. DNA replication—when?
Where?
Why?
What else does a cell do?
When? Where? Why?

2. RNA and Protein Synthesis
What is RNA?
The Structure of RNA:
Similar to DNA long chain of nucleotides (made of phosphate + sugar + base).
Different than DNA because
single stranded
ribose sugar instead of deoxyribose
uracil instead of thymine
Includes three types of RNA: tRNA, mRNA, and rRNA.

3. DNA compared to RNA BOTH made of nucleotide monomers
Contains the sugar deoxyribose
Has the bases A, C, G, and U
Typically double-stranded
Three types of RNA:
mRNA, tRNA, rRNA
Only one type of DNA

5. RNA carries DNA’s instructions.
The CENTRAL DOGMA states that information flows in one direction from DNA to RNA to proteins.

6. The CENTRAL DOGMA includes three processes.
Replication
Transcription
Translation
replication
transcription
translation
RNA is a link between DNA and proteins.

7. BIG PICTURE: Protein Synthesis
DNA
RNA
Protein

8. Transcribe means “to write”
Transcription copies DNA to make a strand of RNA.
(Transcription converts a gene into a single-stranded RNA molecule.)

9. Transcription makes three types of RNA.
Messenger RNA (mRNA) serves as messengers from DNA in nucleus to ribosomes in cytoplasm. The message will be translated to form a protein.
Ribosomal RNA (rRNA) forms structural component of ribosomes (remember, ribosomes make proteins in the cytoplasm).
Transfer RNA (tRNA) transfers each amino acid to the ribosome as specified in a mRNA code.

10. Transcription is catalyzed by RNA polymerase.
RNA polymerase finds an area known as a promoter on the DNA strand. RNA polymerase and other proteins form a transcription complex.
The transcription complex recognizes the start of a gene (DNA) and unwinds a segment of it.
start site
nucleotides
RNA polymerase + proteins =
transcription complex

11. RNA polymerase moves along the DNA
3. The DNA is used as a template for RNA polymerase to add mRNA nucleotides. Nucleotides pair with one strand of the DNA: C-G and A-U
4. RNA polymerase bonds the nucleotides together.
The DNA helix winds again as the gene is transcribed.
DNA
RNA polymerase moves along the DNA

12. 5. The mRNA strand detaches from the DNA once the gene is transcribed
5. The mRNA strand detaches from the DNA once the gene is transcribed. The mRNA strand is “processed” (cleaned up) and then exits the nucleus.
RNA

13. Practicing transcription
Use the following DNA sequence to complete an RNA transcript. Remember. Thymine is not a base for RNA; use Uracil as a replacement.
DNA: T A C C G C T T A A C C G T A A C T
mRNA:

14. The transcription process is similar to replication.
Transcription and replication both involve complex enzymes and complementary base pairing.
The two processes have different end results.
Replication copies all the DNA; transcription copies a gene.
Replication makes one copy; transcription can make many copies.
growing RNA strands
DNA
one
gene

15. The CENTRAL DOGMA includes three processes.
Replication
Transcription
Translation
replication
transcription
translation
RNA is a link between DNA and proteins.

16. KEY CONCEPT TRANSLATION converts an mRNA message into a polypeptide, or PROTEIN.

17. The CENTRAL DOGMA includes three processes.
Replication
Transcription
Translation
replication
transcription
translation
RNA is a link between DNA and proteins.

18. The Genetic Code There are only 4 RNA bases (A U C G)
How are there 20 different amino acids if only 4 letters make up the alphabet of RNA?
RNA bases are taken 3 at a time
A CODON is a sequence of three consecutive nucleotides on the mRNA strand that specify/code for a single amino acid.
Anticodons are the “complements” of the mRNA codons
Anticodons are on tRNA molecules that travel throughout the cytoplasm picking up the correct amino acids.

19. Amino acids are coded by mRNA base sequences.
Translation converts mRNA messages into polypeptides.
A codon is a sequence of three nucleotides that codes for an amino acid.
codon for
methionine (Met)
leucine (Leu)

20. Amino acids are linked to become a protein.
An anticodon is a set of three nucleotides that is complementary to an mRNA codon.
An anticodon is carried by a tRNA.

21. Ribosomes consist of two subunits.
The large subunit has three binding sites for tRNA.
The small subunit binds to mRNA.

22. 1. For translation to begin, tRNA binds to a start codon and signals the ribosome to assemble.
2. A complementary tRNA molecule binds to the exposed codon, bringing its amino acid close to the first amino acid.

23. 3. The ribosome helps form a polypeptide bond between the amino acids and tRNA lets go of amino acid.
4. The ribosome pulls the mRNA strand the length of one codon.

24. 5. The now empty tRNA molecule exits the ribosome.
6. A complementary tRNA molecule binds to the next exposed codon.
7. Once the stop codon is reached, the ribosome releases the protein and disassembles.

25. DNA ---- mRNA -- tRNA --- proteins codons anticodons amino acids
Some finer points…
DNA ---- mRNA -- tRNA --- proteins
codons anticodons amino acids
AUG is an mRNA START codon
There are three STOP codons.
UAA, UAG, and UGA

26. The genetic code matches each codon to its amino acid or function.
The genetic code matches each RNA codon with its amino acid or function.
three stop codons
one start codon, codes for methionine

27. Practicing transcription
Use the following DNA sequence to complete an RNA transcript. Remember. Thymine is not a base for RNA; use Uracil as a replacement.
DNA: T A C C G C T T A A C C G T A A C T
mRNA: A U G G C G A A U U G G C A U U G A
tRNA: U A C C G C U U A A C C G U A A C U
Amino Met Ala Asn Try His STOP
acid: (START)

28. A change in the order in which codons are read changes the resulting protein.
Regardless of the organism, codons code for the same amino acid.

30. The EXPRESSION of genes is carefully REGULATED in cells.
Gene Expression and Regulation
Are ALL genes “on” all the time in the life of a cell?
Do skin cells need to make digestive enzymes?
Do kidney cells need to make hemoglobin?
Do muscle cells need to make amylase?
How do cells control what they make/do?
The EXPRESSION of genes is carefully REGULATED in cells.
Just remember: a cookbook is full of recipes, but you don’t make all of them every time you make a meal. You just pick and choose what you want to cook and make those items from those select recipes.

31. KEY CONCEPT Gene expression is carefully regulated in both prokaryotic and eukaryotic cells.

32. Prokaryotic cells turn genes on and off by controlling transcription.
A promotor is a DNA segment that allows a gene to be transcribed.
An operator is a part of DNA that turns a gene “on” or ”off.”
An operon includes a promoter, an operator, and one or more structural genes that code for all the proteins needed to do a job.
Operons are most common in prokaryotes.

33. Eukaryotes regulate gene expression at many points.
Different sets of genes are expressed in different types of cells.
Transcription is controlled by regulatory DNA sequences and protein transcription factors.

34. Transcription is controlled by regulatory DNA sequences and protein transcription factors.
Most eukaryotes have a TATA box promoter.
Enhancers and silencers speed up or slow down the rate of transcription.
Each gene has a unique combination of regulatory sequences.

35. RNA processing is also an important part of gene regulation in eukaryotes.
mRNA processing includes three major steps.

36. mRNA processing includes three major steps.
Introns are removed and exons are spliced together.
A cap is added.
A tail is added.

37. KEY CONCEPT Mutations are changes in DNA that may or may not affect phenotype.

38. A mutation is a change in an organism’s DNA.
Some mutations affect a single gene, while others affect an entire chromosome.
A mutation is a change in an organism’s DNA.
Many kinds of mutations can occur, especially during replication.
A point mutation substitutes one nucleotide for another.
mutated
base

39. Many kinds of mutations can occur, especially during replication.
A frameshift mutation inserts or deletes a nucleotide in the DNA sequence.

40. Chromosomal mutations affect many genes.
Chromosomal mutations may occur during crossing over
Chromosomal mutations affect many genes.
Gene duplication results from unequal crossing over.

41. Translocation results from the exchange of DNA segments between nonhomologous chromosomes.

42. Mutations may or may not affect phenotype.
Chromosomal mutations tend to have a big effect.
Some gene mutations change phenotype.
A mutation may cause a premature stop codon.
A mutation may change protein shape or the active site.
A mutation may change gene regulation.
blockage
no blockage

43. Some gene mutations do not affect phenotype.
A mutation may be silent.
A mutation may occur in a noncoding region.
A mutation may not affect protein folding or the active site.

44. Mutations in body cells do not affect offspring.
Mutations in sex cells can be harmful or beneficial to offspring.
Natural selection often removes mutant alleles from a population when they are less adaptive.

45. Mutations can be caused by several factors.
Replication errors can cause mutations.
Mutagens, such as UV ray and chemicals, can cause mutations.
Some cancer drugs use mutagenic properties to kill cancer cells.