RNA (Dr Curran) Flashcards
What can altered DNA sequences cause?
- protein function and structure is essential to biological wellbeing
- altered DNA sequences can be associated with altered proteins
- altered proteins can be associated with altered phenotypes
What is necessary to convert DNA code to proteins?
- converting 2-dimensional DNA code into 3-D protein function requires:
- INTERMEDIARY MOLECULES WITH ASPECTS OF BOTH LANGUAGE
- also known as ribonucleic acid (RNA)
What are the differences between DNA and RNA?
-DNA: • has a deoxyribose sugar. • is double stranded. • consists of ATGC. • has a very regular secondary structure -RNA: • has a ribose sugar. • is single-stranded. • consists of AUGC. • has a highly variable secondary structure.
What are the types of RNA?
+Messenger RNA (mRNA)
- An RNA transcript of DNA code.
+Transfer RNA (tRNA)
- An adapter RNA molecule that interfaces with single amino acids.
+Ribosomal RNA (rRNA)
- Aligns the message in a ribosome so that the codons can be decoded.
- Plays a key role in catalysing the joining of amino-acids together
What is the first step in turning the DNA code into a phenotype?
- Transcription
- correct DNA sequence must be identified
- then accessed (use of rna polymerase)
- then copied (transcribed) into mRNA
What is the second step in turning the DNA code into a phenotype?
- Translation
- translating mRNA into protein language
- tRNA is used to add amino acids and form a polypeptide chain
- mRNA is read by ribosome which attaches correct tRNA anticodons to codons to allow amino acids to attach (read in triplets)
Why is mRNA called a molecular photocopy?
• Exists as discrete segments of information
• Usually exists in multiple copies
• Is not as robust as the original
• Creates great flexibility with respect to how
the information is used
How does transcription work?
- RNA polymerase slides along the DNA creating an open complex as it moves
- the DNA strand known as the template strand is used to make a complementary copy of RNA (mRNA)
- the RNA is synthesized in a 5’ to 3’ direction using ribonucleoside triphosphates as precursors
- complementary bases the same except for U instead of T in RNA
What type of terminations exist?
-Rho Independent Termination
+DNA has self complementary sequence
+RNA has complementary sequences built in
+RNA snaps off when it has finished transcribing (UUUU to AAAA)
-Rho Dependent Termination 1
+Rho protein binds on site on RNA called ρ recognition site and chases the RNA polymerase
+ATP is hydrolyzed
+weakens interaction between template and transcript, causing them to dissociate ρ and polymerase also dissociate
What is the structure of tRNA like?
- Each tRNA molecule has a primary secondary and tertiary structure
- amino acid on one end
- anticodon on one loop
- Aminoacyl-tRNA syntetase catalyzes attachment of tRNAs to corresponding amino acid (charges the RNA)
What are ribosomes?
- ribosome = two subunits
- Ribosomes are sites of polypeptide synthesis
- Ribosomes are complex structures composed of RNA and protein
- Prokaryotic: 70S
- Eukaryotic:80S
How does translation work?
• Ribosomes are the protein factories of the cell
• They slide along the message exposing three bases at a time
• Specific adapter molecules (tRNAs) interpret the message into the language of amino acids
• Initiation sets stage for polypeptide synthesis
– AUG start codon at 5’ end of mRNA (small subunit)
– Formalmethionine (fMet) on initiation tRNA and big subunit binds after
• First amino acid incorporated in bacteria
• Elongation during which amino acids are added to
growing polypeptide
– Ribosomes move in 5’-3’ direction revealing codons
– Addition of amino acids to C terminus (A site)
-move to P site,polypeptide forms, exit from E site
– 2-15 amino acids per second
• Termination which halts polypeptide synthesis
– Nonsense codon recognized at 3’ end of reading frame
– Release factor proteins and halt polypeptide synthesis (ribosomal unit dissociates/disbands)
What is a wobble or wobble position?
Wobble: Some tRNAs recognize more than one codon for amino acids they carry
-wobble position is the base that can be interpreted differently (always third base)
What role does rRNA have?
-rRNA Plays a key role in catalysing the joining
of amino-acids together.
-responsible for making the peptide bond formation
What are the differences and similarities between prokaryotes and eukaryotes?
Prokaryotes:
-no nucleus, transcription and translation take place in same compartment sometimes coupled
-no exons and introns
+transcription:
-one RNA polymerase/ five subunits
-primary transcripts are mRNAs, triphosphate start and no tail
+translation:
-formylmethionine initiator RNA
-multiple ribosome binding sites
-small ribosomal subunit immediately binds to mRNA binding site
Eukaryotes:
-nucleus and nuclear membrane, transcription in nucleus while translation in cytoplasm
-DNA of a gene is made up of exons and introns, splicing deletes introns
+transcription:
-many kinds of RNA polymerase/ 10 subunits or more
-primary transcripts undergo processing to form mRNA, methylated cap and poly-a-tail
+translation:
-initiator tRNA methionine
-only one start site
-small ribosomal unit binds to methylated cap then scans for the binding site
What happens to RNA in Eukaryotes?
-In eukaryotes, RNA is processed after transcription:
• A 5’ methylated cap is added.
• The addition of a 3’ Poly-A tail targets it out of the nucleus. (poly-a-polymerase adds As onto 3’ end)
• The molecules are frequently spliced to generate mature messages
What is RNA splicing?
-RNA molecules are often processed by splicing.
-RNA splicing removes introns
• Exons – sequences found in a gene’s DNA and mature mRNA (expressed regions)
• Introns – sequences found in DNA but not in mRNA (intervening regions)
• Some eukaryotic genes have many introns
• Splicing is catalyzed by spliceosomes
– Ribozymes – RNA molecules that act as enzymes
– Ensures that all splicing reactions take place in concert
+one gene= many outcomes
