1. DNA makes RNA Single helix Ribose sugar A - U pair Double helix
Deoxyribose
A - T pair
DNA segments - genes - code for POLYPEPTIDES
PROTEIN > TRAIT
Copies and translates the gene code

2. • transcribed into mRNA
• code for polypeptide
• builds proteins the body needs
Coding DNA
Non-coding DNA
• Differences in DNA sequence = differences in gene expression

3. Types of RNA
Messenger, mRNA, is synthesized from a gene and carries the code into the cytoplasm for protein synthesis
Si RNA is double stranded

4. Types of RNA
amino acid
Transfer (tRNA) loops of nucleotides, three of which form an anticodon.
Also holds the amino acid coded for by the mRNA codon complement.
The polypeptide is built by linking the amino acids of adjacent tRNA.
Si RNA is double stranded
anticodon

5. Types of RNA
Ribsomal, rRNA, combines with protein in the cytoplasm to form a ribosome
Synthesized in two sub units
Si RNA is double stranded

6. Types of RNA
Small, interfering RNA (siRNA) ; RNA interference (RNAi); microRNA (miRNA)
small sequences of RNA that bind to cellular RNA, interfering with the production of the protein
Si RNA is double stranded
application

7. The Ribosome • The site of protein synthesis
• holds mRNA/tRNA in position as the protein is synthesized
tRNA sites
mRNA site

8. The Central Dogma gene expression Fundamental & universal to life on Earth
Genes in the DNA
transcribed into
RNA which is
translated into
a protein

9. Transcription: DNA as Template for mRNA via the base-pair rule
nearly the same as mRNA code
coding (sense) strand
The template strand is ALWAYS read in the 3' to 5' direction (that is, starting from the 3' end of the template and reading the nucleotides in order toward the 5' end of the template). The new strand (since it is complementary) MUST BE SYNTHESIZED in the 5' to 3' direction (remember that both strands of a DNA molecule are described as being antiparallel). Polymerase catalyzes the formation of the hydrogen bonds between each arriving nucleotide and the nucleotides on the template strand.
In addition to catalyzing the formation of Hydrogen bonds between complementary bases on the template and newly synthesized strands, DNA polymerase also catalyzes the reaction between the 5' phosphate on an incoming nucleotide and the free 3' OH on the growing polynucleotide (what we know is called a phosphodiester bond!). As a result, the new DNA strands can grow only in the 5' to 3' direction, and strand growth must begin at the 3' end of the template,
anti-sense strand
complementary to mRNA
Animation

10. Transcription is initiated when RNA polymerase binds at the DNA preceding the gene, the promoter
The first step in transcription is initiation, when the RNA polymerase binds to the DNA upstream (5′) of the gene at a specialized sequence called a promoter. In bacteria, promoters are usually composed of three sequence elements, whereas in eukaryotes, there are as many as seven elements. In eukaryotes, the "core" promoter for a gene transcribed by pol II is most often found immediately upstream (5′) of the start site of the gene. Most pol II genes have a TATA box (consensus sequence TATTAA) 25 to 35 bases upstream of the initiation site, which affects the transcription rate and determines location of the start site. The terms "strong" and "weak" are often used to describe promoters and enhancers, according to their effects on transcription rates and thereby on gene expression. Alteration of promoter strength can have deleterious effects upon a cell, often resulting in disease. For example, some tumor-promoting viruses transform healthy cells by inserting strong promoters in the vicinity of growth-stimulating genes, while translocations in some cancer cells place genes that should be "turned off" in the proximity of strong promoters or enhancers. Terminator sequences are found close to the ends of coding sequences.
Elongation – polymerase adds nucleotides to transcribe the gene. Termination sequences near the end of the gene communicate a stop-transcription message

11. Translation: mRNA sequence rewritten into a chain of amino acids
tRNA base pair with mRNA at ribosomes
mRNA carries the gene code from the nucleus
rRNA builds the ribosome subunits
animation

12. Polypeptide
Amino acid
Peptide (covalent) bonds
Anticodon of tRNA
Codon of mRNA

13. The triplicate code is redundant but never ambiguous
6 codons for serine!
but never ambiguous
CCC = proline, only

14. Segments of genes – exons – are identified for transcription*
*eukaryotes only
via splicesomes
Thus creating many different mRNA from one gene
30,000 genes -> +100,000 proteins

15. Caps and tails are added to the mRNA, slowing destruction by enzymes
STOP Codon
START codon
Methyl CAP at 5’ end
Poly–A TAIL

16. Mutations in a gene change the code and often, the polypeptide
Point mutation (substitution, missense)
• Potentially changes one amino acid
• Protein produced, but folding may be altered

17. Frameshift mutations result from insertion or deletion of nucleotides
•Alters the codons from that point on
•Often no functional protein produced

19. Summary of Differences
Replication Transcription & Translation
Copies both DNA helices Uses template strand of DNA to create RNA
Leads to more cells Leads to proteins
(gene expression)
Entire molecule copied Single gene transcribed, exons spliced together
DNA polymerase adds nucleotide RNA polymerase adds nucleotides
RNA primer initiates sequencing Promoter on DNA initiates sequencing