changes in the genetic material. can affect the genetic blueprint by altering gene function.
inborn error of metabolism
refers to a mutation in a gene that is inherited from one or both parents.
common bread mold. requires only a few nutrients: a carbon source (sugar), inorganic salts, and one vitamin known as biotin
produce an RNA molecule that contains the information to specify a polypeptide with a particular amino acid sequence
an RNA molecule that contains the information to specify a polypeptide with a particular amino acid sequence. job is to carry information from the DNA to ribosomes.
2 additional steps between transcription and translation in eukaryotes
during RNA processing, the RNA transcript, termed pre-mRNA, is modified in ways that make it a functionally active mRNA.
number of proteins in bacteria and eukaryotes
bacterium can make a few thousand different proteins, estimates for eukaryotes range from several thousand in simpler eukaryotes to tens of thousands in more complex eukaryotes like humans
an organized unit of DNA sequences that enables a segment of DNA to be transcribed into RNA and ultimately results in the formation of a functional product
when a ___ ____ binds to a regulatory sequence, the rate of transcription is affected. some ___ _____ enhance the rate of transcription, while others inhibit it
a recognition step. completed when the DNA strands are separated near the promoter to form an open complex
in bacteria such as E. coli, a protein called ____ ____, binds to RNA polymerase. also recognizes the base sequence of a promoter and binds there. causes RNA polymerase to specifically bind to a promoter and binds there.
RNA polymerase synthesizes the RNA transcript. sigma factor is released and RNA polymerase slides along the DNA in a way that maintains an open complex as it goes.
the opposite DNA strand from the template strand. has the same sequence of bases as the mRNA (except U for T)
RNA polymerase reaches a terminator, which causes it and the newly made RNA transcript to dissociate from the DNA.
RNA polymerase II
in eukaryotes, responsible for transcribing the mRNA from eukaryotic structural genes. always requires five general transcription factors to initiate transcription.
RNA polymerases I and III
in eukaryotes, transcribe nonstructural genes such as the genes that encode tRNAs and rRNAs.
pre-mRNA undergoes a process in which the introns are removed and the remaining exons are connected to each other.
introns are removed from eukaryotic pre-mRNA by a large complex called a _____ that is composed of several different subunits known as snRNPs
enables a single gene to encode two or more polypeptides with differences in their amino acid sequences.
mature mRNAs of eukaryotes have a modified guanosine covalently attached at the 5' end. occurs while pre-mRNA is being made by RNA polymerase, usually when the transcript is only 20 to 25 nucleotides in length.
7-mehtylguanosine structure, is recognized by cap-binding proteins, which are needed for the proper exit of mRNAs from the nucleus. after an mRNA is in the cytosol, the cap structure is recognized by other cap-binding proteins that enable the mRNA to bind to a ribosome for translation
poly A tail
at the 3' end, most mature eukaryotic mRNAs have a string of adenine nucleotides, typically 100 to 200 nucleotides in length. a long one aids in the export of mRNAs from the nucleus. it also cuases a eukaryotic mRNA to be more stable and thereby exist for a longer period of time in the cytosol. the poly A tail is not encoded in the gene sequence. instead, the tail is added enzymatically after a pre-mRNA has been completely transcribed.
poly A tail in bacteria
has an opposite affect. causes the mRNA to be rapidly degraded. not well understood.
Meselson and Jacob
1960. found that proteins are synthesized on cellular structures known as ribosomes and that the information comes from mRNA.
specifies the relationship between the sequence of nucleotides in the mRNA and the sequence of amino acids in a polypeptide
the genetic code is read in groups of three nucleotide bases known as _____. total of 64 different _____. 4^3=64
the genetic code is said to be _____ because more than one codon can specify the same amino acid. in most instances, the third base in the codon is the degenerate or variable base.
a region that specifies the amino acid sequence of a polypeptide. consists of a series of codons.
specifies the amino acid methionine. only a few nucleotides from the ribosomal-binding site. defines the reading frame of an mRNA.
a three-base sequence in a tRNA molecule that is complmentary to a codon in mRNA. corresponds to the amino acid that it carries.
enzymes that catalyze the attachment of amino acids to tRNA molecules. cells make 20 distinct types for each amino acid.
aminoacyl-TRNA synthetase mechanism
1. a specific amino acid and ATP are recognized by the enzyme.
2. amino acid is activated by the covalent attachment of an AMP molecule, and pyrophosphate is released
3. the activated amino acid is covalently attached to the 3' end of a tRNA molecule., and AMP is released.
4. the tRNA with its attached amino acid, called charged tRNA or aminoacyl tRNA, is released from the enzyme.
the second genetic code
the ability of each aminoacyl-tRNA synthetase to recognize an appropriate tRNA. the wrong amino acid is attached to tRNA less than once in a 100,000 times.
1964. Proposed a two-site model for tRNA binding to the ribosome. these sites are known as the peptidyl site (P site) and aminoacyl site (A site)
a complex is formed between an mRNA molecule, the first tRNA, and the ribosomal subunits. in all species, the assembly of this complex requires the help of proteins called initiation factors that facilitate the interaction between these components. the assembly also requires an input of energy. GTP is hydrolyzed by certain initiation factors.
recognizes the start codon in mRNA and binds to it. in eukaryotes, carries methionine, in bacteria carries a methionine that has been modified by the attachment of a formyl group.
translation-difference in initiation between eukaryotes and bacteria
1. instead of a ribosomal-binding sequence, eukaryotic mRNAs have a guanosine cap at their 5' end. this 5' cap is recognized by cap-binding proteins that promote the binding of the mRNA to the small ribosomal subunit
2. the location of the start codon in eukaryotes is more variable
1978. proposed that the small ribosomal subunit identifies a start codon by beginning at the 5' end and then scanning along the mRNA in the 3' direction in search of an AUG sequence.
AUG, a guanine just past the start codon and the sequence of six bases directly upstream from the start codon are also important for start codon selection.
rate of translation
15 to 18 amino acids per second in bacteria. 6 amino acids per second in eukaryotes.
the hydrolysis of GTP by proteins that function as _____ _____ provides teh energy for the binding of the tRNA to the A site.
peptidyl transfer reaction
the polypeptide is removed from the tRNA in the P site and transferred to the amino acid at the A site.
a region of the 50S subunit that catalyzes the peptidyl transfer reaction.
propsoed that hte rRNA is responsible for catalyzing the peptide bond formation between adjacent amino acids. ribosome is a robzyme.