Chapter 14 Flashcards
In bacteria what two processes occur at the same time and why?
Transcription and translation due to no compartmentalization
Primary transcript
Pre-mRNA
An initial RNA transcript from any gene; also called pre-mRNA when transcribed from a protein-coding gene.
Codons are written in which direction
5’-3’
Triplet code
The genetic instructions for a polypeptide chain are written in the DNA as a series of non overlapping, three nucleotide codes
UAA, UAG, UGA
Stop codon
AUG
Start signal and methionine
Promoter
DNA sequence where RNA polymerase attaches and initiates transcription
Terminator
In bacteria, the sequence that signals end of transcription.
Bacteria have one type of RNA polymerase that synthesizes mRNA and other types of rna how many do eukaryotes have?
3- RNA polymerase, pre-mRNA, RNA polymerase 3 (synthesis)
Start point
In transcription, the nucleotide position on the promoter where RNA polymerase begins synthesis of RNA
Transcription factors
A regulatory protein that binds to DNA and affects transcription of specific genes.
Transcription initiation complex
The completed assembly of transcription factors and RNA polymerase bound to a promoter.
Initiation
After RNA polymerase binds to the promoter, the DNA strand unwinds and the polymerase initiates RNA synthesis at the start point on the template strand.
Elongation
The polymerase moves downstream, unwinding the DNA and elongating the RNA transcript in 5’-3’
Termination
RNA transcript is released, and the polymerase detached from the DNA.
Tata box
A DNA sequence in eukaryotic promoters crucial in forming the transcription initiation complex.
Termination in eukaryotes
RNA polymerase 3 transcribes a sequence on the DNA called the polyadenylation signal sequence, which specifies a polyadenylation signal (AAUAAA) in the pre-mRNA. Then 10-30 nucleotides downstream 5ese proteins cut the RNA transcript free from polymerase.
RNA processing
Modifications to pre-mRNA
- splicing out of introns
- joining Exons
- alteration of 5’-3’ ends (5’ end receives 5’ cap, 3’ end receives poly-A tail. These facilitate export of mRNA out from nucleus, protect from degradation by enzymes, help ribosomes attach to 5’ end.)
RNA splicing
after synthesis of eukaryotic pre-mRNA, the removal of portion (introns) that will not be included in the mrna.
Intron
A non-coding sequence within pre-mRNA that is removed.
Spliceosome
Large complex of proteins and small DNA’s that remove introns
Ribozymes
An rna molecule that function as an enzyme such as an intron that catalyzes its own removal during RNA splicing.
Transfer rna
An rna molecule that functions as a translation between nucleic acid and protein languages by picking up specific amino acids and carrying it to the ribosome, where the rna recognizes the appropriate codon in the mRNA,
Anti codon
Particular nucleotide triplet that base-pairs to a specific mRNA codon (3’-5’)
Aminoacyl tRNA synthetases
An enzyme that joins each amino acid to the appropriate tRNA . (20 different)
-uses hydrolysis of ATP
Three binding sites of ribosomes and function
P-site= holds the tRNA carrying the growing polypeptide chain
A-site=Holds the tRNA carrying the next amino acid to be attached to the chain.
E-site= Where discharges tRNAs leave the ribosome
Initiation of translation
- Small subunit binds to the mRNA, initiator tRNA with anticodon UAC base pairs with the start codon AUG.
- Arrival of large subunit. Initiation factors bring all components in p site together.
Elongation of translation
Amino acids are added one by one to previous acid at the c terminus
Termination of translation
Elongation continues until stop codon in mRNA reaches A-site. Release factor (protein) beings to the stop codon causing addition of H2O molecule instead of amino acid. Creates hydrolysis and breaks bond between polypeptide and the tRNA in p site.
Post translation modifications
- addition of sugars, lipids, phosphate group….
- removal of 1+ amino acids
- chain may be cleaved into pieces
- 2 chains may attach (quaternary structure)
Signal peptide
A sequence of 20 amino acids at or near the leading amino acid end of a polypeptide that targets it to the ER or other organelle.
Signal-recognition particle
A protein RNA complex that recognized a signal peptide as it emerges from a ribosome and helps direct the ribosome to the ER by binding to a receptor protein on the ER.
DNA Polymerase 1 function
Removes rna primer and adds DNA
Point mutation
Changes In a Single nucleotide pair of a gene
Nucleotide- pair substitution
Replacement of 1 nucleotide and its partner with another pair of nucleotides. (Some have no effect)
Silent mutation
Substitution with no observable effect on the phenotype
Missense mutations
Substitutions that change one amino acid to another
Non-sense mutation
Point mutation that changes a codon for a stop codon
Frameshift mutation
The number of nucleotides inserted or deleted is not a multiple of 3. Effects all further nucleotides.
Mutagens
Physical or chemical agents that cause mutations of DNA
X-rays, UV light
Nucleic acid hybridization
Fluorescent probes base pair to a sequence
Ex: telomeres
DNA amplification with PCR
Take target DNA, denature it, cool and add primers, polymerase, and end up with two copies of DNA. Can produce billions of copies of a gene in few hours.
CRISPR-CAS 9 system
Bacterial based system Cas 9 is a nucleus which cuts double stranded DNA uses a guide rna to go to a place Cleaves DNA and adds “good” DNA Or cleaves bad DNA from a gene.
UTR
Untranslated region- not removed, but non coding, these recognize ribosomes
In translation what entero source is used
GTP
Poly ribosomes
In both euk and prok. Multiple ribosomes translate single mRNA at once
