DNA
• Structure
• Replication
• Functions (Stores and provides copies of
genetic material- genes)
– Blueprint (genes) for Protein Synthesis (Enzymes
and cell building blocks)
Francis Crick
RNA (Ribonucleic Acid)
• Why do we need RNA?
• Why can’t DNA directly make proteins?
• Where is DNA located? Can it leave? Why
does it stay there?
• Where are proteins made?
• Temporary copies of parts of the blueprint
• Ribonucleic acid (RNA)
– carries DNA’s instructions
– acts as an link between DNA in the nucleus and
protein synthesis in the cytoplasm.
– plays several different roles in protein synthesis.
Similarities DNA and RNA
• Both are nucleic acids
• Both are made up of nucleotides (sugar, base,
phosphate)
DNA versus RNA
DNA versus RNA
Differences between DNA and RNA
DNA
RNA
Genes expression is through protein
synthesis
Types of RNA
1. Messenger RNA (mRNA)
-formed in nucleus from DNA template
-Carries copies of instructions for protein synthesis to the ribosomes in cytoplasm
(nuclear membrane pores)
2. Ribosomal RNA (rRNA)
-along with some proteins make up ribosomes (cytoplasm)
3. Transfer RNA (tRNA)
- transport amino acids to ribosomes (cytoplasm)
All types of RNA are formed in the nucleus.
Transfer RNA
Transcription
• Messenger RNA (mRNA) is made from DNA
– DNA is template
– Complementary RNA is produced
– Nucleus (eukaryotic cells)
– RNA polymerase (unwinds the DNA and adds
nucleotides to form RNA)
– Uracil is paired with adenine
Transcription steps
• RNA polymerase binds to promoter (“start”)
region of gene
• RNA polymerase unwinds and separates the
two strands of DNA
• RNA polymerase adds complementary RNA
nucleotides
• RNA polymerase reaches a sequence of
nucleotides on the gene that signals “stop”
• RNA polymerase detaches
Transcription
Transcription
Template versus Nonsense Strand
• http://www.dnai.org/a/index.html
• What does this remind you of?
• Practice creating complementary mRNA
Post-transcription
• Pre-mRNA molecule
produced and undergoes
processing and editing.
– Introns – cut out and
discarded
– Exons – remaining pieces
spliced back together to
form mRNA
• mRNA travels through
nuclear membrane pore
into cytoplasm
Transcription leads to Translation
Exon – expressed as a protein
Intron – DNA that isn’t expressed (inhibited)