RNA & Protein Synthesis How does DNA make the proteins that make living things?
RNA RiboNucleic Acid Made of nucleotides * 5 carbon sugar (ribose) *phosphate group *nitrogenous bases (A,U,C,G) There are 3 types of RNA: 1) rRNA - (ribosomal RNA) 2) tRNA - (transfer RNA) 3) mRNA -(messenger RNA)
Some important differences between DNA & RNA 1) RNA uses a different 5 carbon sugar! Ribose instead of Deoxyribose 2) RNA is a single strand, DNA is a double strand 3) RNA uses uracil instead of thymine
Protein Synthesis DNAmRNAprotein
Protein synthesis Includes 2 processes: TRANSCRIPTION & TRANSLATION! Uses many enzymes… Makes a “copy” of instructions from the DNA and sends those copies to the ribosome to make a specific protein.
Transcription Process of making mRNA from a strand of DNA. Happens in the nucleus. Only uses one side of the DNA RNA polymerase is the major enzyme used Starts at a “promoter” on the DNA…this is the start of the gene. RNA nucleotides are added to the complimentary strand on one side of DNA until the “termination” portion is reached.
Transcription
mRNA Has a triplet codon (a sequence of 3 nitrogen bases, like AGC or UAC) The codons code for the same amino acids in almost all living things.
The Universal Genetic Code
Another way to display it…
Tweaking the RNA Some of the stuff on DNA is “junk”. mRNA is “edited” to cut introns from the mRNA. (Using special enzymes!) The “good” parts, exons, are kept and “pasted” together to make the expressed part of the gene…the stuff that actually gets made!
Example: I’ve had a bad day. Farleyfarleyfarley Hafharl. Bolrnt daffigty coombin snagglefahrt. I sat down on the couch with a bowl of cereal. Axd nadherul klahsur gususj! Then, my cat attacked me. Ukl tolsuie hudla di. She jumped right in the bowl and started drinking the milk! Can you believe that? Naah gouu! You get all that?
Much of that paragraph is nonsense, just like much of the DNA. Also, just like the DNA, it has to be edited to make it sensible.
Using the last example… I’ve had a bad day. I sat down on the couch with a bowl of cereal. Then, my cat attacked me. She jumped right in the bowl and started drinking the milk! Can you believe that? The introns have been removed from the message and now it is ready to be expressed.
Switching gears…now on to: Translation! Makes a protein using tRNA, enzymes and mRNA. Occurs in the ribosome. tRNA has the anticodon (a matching codon that allows the tRNA to attach to the ribosome at the mRNA). mRNA Protein
Translation Steps: 1.) Ribosome “reads” the mRNA one codon at a time (3 bases at a time). 2.) Ribosome “calls” the tRNA that has the anticodon to bring the amino acid. 3.) Amino acid attaches and tRNA is released. 4.) The next codon is read and another amino acid is brought by tRNA and attached to the 1st amino acid. 5.) This continues until the “Stop” codon is reached.
Translation mRNA
The Universal Genetic Code
Another way to display it…
Mutations …are any change in the DNA of an organism. May not have any affect or may cause a major deformation, illness. Mutations are caused by mutagens Mutagens are things like: UV light, viruses, chemicals…
Gene Mutations Point Mutation AUC GGA UCC AUC CGA UCC only 1 codon is affected example: “substitution mutation” AUC GGA UCC AUC CGA UCC THE FAT CAT WAS MAD THE FUT CAT WAS MAD
Gene Mutations Point mutations, because they only affect one codon, can have: 1.) No effect on the overall protein. (neutral) OR 2.) A beneficial effect on the protein. (good) 3.) A negative effect on the protein. (bad)
How could a mutation have NO effect AT ALL???
No effect??? Original DNA: TAC-GGC-CGC-GGA-AAT-ATC Mutated DNA: TAC-GGT-CGA-GGG-GAC-ACT Determine the A.A. sequence coded by both genes.
ANSWER: Met-Pro-Ala-Pro-Leu – [STOP] Same in both the original and mutated DNA. This is called Redundancy.
More Gene Mutations Frameshift Mutations – AAU CGA GGA … AAC GAG GA… will affect several if not all of the following codons! (MAJOR PROBLEM!) Example: “Deletion” – one base was left out. AAU CGA GGA … AAC GAG GA… (What is missing?)
Did this make a difference in the amino acid sequence??? AAU CGA GGA … AAC GAG GA… Find the a.a. sequence for the left side: Asn – Arg – Gly Find the a.a. sequence for the changed side: Asn – Glu – (either Glu or Asp)
So what happened? The a.a. sequence changed from: Asn – Arg – Gly to… Asn – Glu – (either Glu or Asp) This is bad. It changes the entire protein, making the protein not able to do its intended job. (Like changing the shape of a key makes it not fit in the lock.)
Back to the Fat Cat… THE FAT CAT WAS MAD… THE FAC ATW ASM AD… Deletions cause a shift in the codons…just like leaving a letter out, it makes no sense!
Other Frameshift Mutations: “Insertion” – an extra base is added. ACC GAU GUC… ACU CGA UGU C… (What was added?)
THE FAT CAT WAS MAD THE FAD TCA TWA SMA D… Once again, this makes no sense!
Chromosome Mutations …are usually damaging. An entire piece of a chromosome may be deleted, moved or damaged. ALL INFORMATION ON THE AFFECTED SECTION MAY BE LOST OR FOREVER CHANGED (and is useless).
Types of Chromosome Mutations Deletion – the whole chromosome is gone! Duplication – now you have 2 sets of the same stuff. Inversion – one part of a chromosome gets moved to another area on the SAME chromosome. Translocation – a section of a chromosome is stuck on a DIFFERENT chromosome
Chromosome Mutations