Bio Chapter 12
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From Genes to Proteins
Genes are coded DNA instructions that control the production of proteins. DNA never leaves the nucleus, therefore the code must be copied into RNA, or ribonucleic acid.
Serve as messenger from DNA to the rest of the cell.
Type of RNA that makes up parts of ribosomes.
Transfers each amino acid to the ribosome as it is specified by the mRNA
Known as the silencing RNA. It helps by influencing which RNAs are translated.
- DNA-> RNA
- Transcription requires an enzyme known as RNA polymerase
- During transcription, RNA polymerase binds to DNA and separates the DNA strands. RNA polymerase then uses one strand of DNA as a template from which nucletoides are assembled into a strand of RNA.
- 5 Prime to 3 Prime
- Is for mRna, tRna and rRna
Step One of Transcription
Rna plymerase binds to the promoter site. RNA polymerase hooks together RNA nucleotides as they base pair along the DNA template.
Promoter DNA sequence 5'TATAAA_3'
Step 2 of Transcription
RNA plymerase moves along DNA template. It unwinds 10-20 DNA bases at a time. RNA polymerase adds nucleotides in the 5->3 direction. As RNA polymerase moves along, the DNA double helix reforms. The new section of RNA 'peels away' as the double helix reforms.
Step 3 of Transcription
- Transcription stops when RNA polymerase reaches a section of DNA called the terminator. Terminatior sequence= AAuAA
- Next, the RNA strand is released and RNa polymerase dissociates from the DNA. The RNA strand will go through more processing.
Forming a polypeptide. Uses mRNA as a template for a.a sequence
Three TRNA Binding sites
- 1. A site= holds tRNA that is carrying the next amino acid to be added
- 2. P site= holds tRNA that is carrying the growing polypeptede chain.
- 3. E site= where discharged tRNAs leave the ribosome
- mRNA-> Ribosome
- Uses tRNA to interpreter of mRNA
Large and Small subunit of ribosomes
each has three binding sites for tRNA on its surface. Each has one binding site for mRNA. Facilitates codon and anticodon bonding.
Initiation Step 1
Brings together mRNA, tRNA and ribosomal subunits
Initiation Step 2
- Small ribosomal subunits binds tomRNA and initiator tRNA
- -Start codon= Aug
- -Start anticodon=Uac
- -Small ribosomal subunit attaches to 5prime end of mRNA
- -downstream from the 5 prime end is start codon AUG (mRNA)
- -After the union of mRNA, tRNA and small subunit, the large ribosomal subnit attaches.
What is needed for initiation of RNA?
tRNA mRNA small and Large subunit
Translation of RNA
Amino acids are added one by one to the first amino acid. Step one Codon recognition, mRNA codon in the A site forms hydrogen bonds with the tRNA anitcodon. Step 2- Peptide bond formation, The polypeptide extending from the P site moves A site to attach to the new a.a.
The tRNA w/ the polypeptide chain in the A site translocated to the P site. tRNA at the P site moves to the E site and leaves the ribosome.
Happens at the stop codon (Uaa, Uag, and Uga) The polypeptides is freed from the ribosome and the reso of the translation assembly comes apart.
Differences in gene expression between the two main types of cells
- Prokaryotes= genes are a continuous streach of DNA
- Eukaryotes= genes are fragmented. fragments are made of exons that are interrupted frequent by non-coding regions called introns.
not involved in coding for proteins
Each polypeptied contains a combination of any or all
of the 20 different amino acids.
The properties of proteins are determined by
the order in which different amino acids are joined together.
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