Biology Chapter 14
What are the two stages of gene expression?
1. Transcription 2. Translation
Usually what is the first codon in the mRNA sequence?
AUG... which corresponds to TAC on tRNA chain
What are the steps of transcription?
Binding and initiation Elongation Termination
What is the central dogma?
DNA -> mRNA -> Proteins (made of amino acids) -> You (credit: Francis Crick)
What happens during termination step of translation?
Elongation continues until a stop codon is encountered. UAA, UAG, UGA. A protein called a release factor binds in the A-site to the termination codon and the ribosomes adds a water molecule to to the end of the now complete polypeptide chain.
Where does translation occur?
In the cytoplasm
What are the steps of translation?
Initiation Elongation Termination
What happens in 'elongation' step of transcription?
RNA Polymerase II moves along the DNA and performs two main functions (i) it untwists the DNA one turn about 10 bases at a time and (ii) adds nucleotides to the 3' end of the growing RNA
What happens during 'binding and initiation' of transcription?
Transcription begins when RNA polymerases bind to the DNA, separate it into two strands and add nucleotides to the 3' end of the growing RNA molecule. A specific initiation sequence identifies the location to begin transcription and a second sequence, the termination sequence terminates the copying. This "transcription unit" is a single gene in eukaryotes (in prokaryotes it may be several functionally related proteins). It consists of the gene and the initiation and termination signals. Initiation and termination sequences are not the same as the start and stop codons. RNA polymerases bind to regions of the DNA known as promoters. The Promoter consists of the initiation site where transcription begins and some dozens of nucleotides upstream from the Initiation site. Certain regions of the promoter must be present for the RNA polymerases to bind. For example, RNA polymerase II keys on a region called the TATA box. The RNA polymerase cannot bind to the DNA directly unless a transcription factor (a protein has bound to the region) first. The RNA polymerase aparently recognizes the complex of the transcription factor and the initiation site together. Once RNA polymerase has bound to the initiation site elongation of the RNA strand can begin.
What happens in 'termination' step of transcription?
Transcription proceeds until the RNA polymerase reaches a termination site on the DNA (the most common stop sequence is AATAAA). At this point, no more RNA nucleotides are added and the mRNA is released.
What happens during elongation step of translation?
Transfer RNA (tRNA) translates the mRNA into the amino acid sequence. tRNA attaches by its anticodon to the codon of mRNA sitting in the A-site. The two amino acids are joined together. The first tRNA is detached , the ribosome moves and the tRNA moves into the P-site and the process is repeated. tRNA gathers amino acids from the cytoplasm and transfers them to the ribosome. One end of the tRNA attaches to a specific amino acid. The other end attaches to an mRNA codon by base pairing with its anticodon. Anticodon is a nucleotide triplet in tRNA that pairs with a complementary codon in the mRNA. tRNa's decde the message codon by codon and as the tRNS'a deposit the amino acids in the correct order, ribosomal enzymes link them into a chain.
What is transcription?
a process that involves the transcribing of genetic information from DNA to RNA. -happens in nucleus
What is 'terminator'?
in bacteria, the sequence that signals the end of transcription
Main point of this chapter is:
the DNA inherited by an organism leads to specific traits by dictating the synthesis of proteins and RNA molecules involved in protein synthesis
What is a 'promoter'?
the DNA sequence where RNA polymerase attaches and initiates transcription
What is translation?
the messenger RNA (mRNA) generated by transcription is interpreted by the ribosome to generate a particular amino acid succession, or polypeptide that will fold into an active protein.
Gene expression is?
the process by which DNA directs the synthesis of proteins (or in some cases, just RNAs)
What happens during Initiation step of translation?
the small ribosomal subunit attaches to the mRNA at the initiation codon site and the first tRNA attaches. Then the big ribosomal subunit attaches with the tRNA in the P-site
What is a 'transcription unit'?
the stretch of DNA that is transcribed into an RNA molecule
What is the 'promoter sequence' in DNA?
upstream from the terminator
What are the link between genotype and phenotype?
proteins
Trait of albinism is caused by:
recessive allele of a pigmentation gene
What is the function of RNA Polymerase?
RNA polymerase binds to DNA, separates the strands, then uses one of the strands as a template from which to assemble nucleotides into a complementary RNA strand.
What 3 codons are stop codons?
UAA, UAG, UGA
Which RNA is used for mRNA synthesis?
RNA polymerase II
