Protein is made outside of the nucleus at the ________.
ribosome
Define transcription
making of mRNA from DNA
messenger RNA is a copy of ___ that can leave the ________.
DNA; nucleus
RNA’s base pairs are read in sets of 3 called ______.
codons
The three stages of transcription are:
- Initiation
- Elongation
- Termination
Give an overview of the initiation stage
starts transcription
Give an overview of the elongation stage
lays down the mRNA nucleotides
Give an overview of the termination
finalizes the mRNA
Describe the promoter
the beginning of the DNA sequence to be copied
What enzyme attaches to the promoter?
RNA polymerase II
Describe the TATA Box
the promoter begins with a sequence of DNA that includes the base pairs T and A
What are transcription factors?
proteins that allow the RNA Polymerase II to bind to the promoter.
What is the transcription initiation complex
the promoter, RNA Polymerase II, and Transcription factors all combined and ready to start transcription
Describe RNA Polymerase
an enzyme that unwinds DNA and lays down RNA nucleotides
A _________ ____ caused the mRNA to be cut free from the DNA.
termination code
When the mRNA is cut from DNA, it is called ___-___ and it needs a few modifications
pre-mRNA
How is the 5’ end of pre-RNA altered
it receives a modified 5′ cap
How is the 3’ end of pre-RNA altered
it a gets a poly-A tail
Describe the 5’ cap
a modified guanine nucleotide with 3 phosphate groups
Describe the poly-A tail
several adenine nucleotides in a row (50+)
What is the purpose of modifying pre-RNA?
- allows mRNA to leave the nucleus
- protects mRNA from hydrolytic enzymes
- helps ribosomes attach to the 5′ end
Describe introns
sections that are cut out of the pre-mRNA
Describe exons
sections that are left in the finalized mRNA
What do spliceosomes do?
carry out RNA splicing
Spliceosomes are made out of what?
ribonucleoproteins (snRNPs)
What do snRNPs do?
recognize the splice sites
Describe ribozymes
catalytic RNA molecules that function as enzymes and can splice RNA
Ribozymes are present in _______.
snRNP’s
What is alternative RNA splicing?
choosing different regions of introns or exons from the same pre-mRNA sequence
What is the purpose of alternative RNA splicing?
So one gene can code for more than one protein
What is t-RNA
Transfer RNA
Each tRNA has an ___-____ that matches up with a codon on the messenger RNA
anti-codon
Each tRNA also has a particular ______ ___ attached to it.
amino acid
aminoacyl-tRNA synthetase
enzyme that attaches amino acids to tRNA
What do ribosomes do in protein synthesis?
Ribosomes match the tRNA anticodons with mRN
The two ribosomal subunits are made of what?
proteins and ribosomal RNA (rRNA)
small subunit holds ____
mRNA
large subunit holds ____
tRNA
A ribosome has three _______ ___ for tRNA
binding sites
What is the A-Site for?
holds the tRNA that carries the next amino acid to be added to the chain
What is the P-Site for?
holds the tRNA that carries the growing polypeptide chain
What is the E-Site for?
the exit site, where discharged tRNAs leave the ribosome
What is polyribosome (or polysome)
several ribosomes translate a single mRNA simultaneously, allowing a cell to make many copies of a protein very quickly
What is a signal peptide
a short peptide added to the finished protein
What does a signal-recognition particle (SRP) do?
attaches to the signal peptide that that it may enter the ER
