Chapter 17 : Gene Expression -From Gene To Protein Flashcards
Transfer of information from DNA to mRNA
Transcription
Transfers information from mRNA to a polypeptide (changing from language of nucleotides to amino acids)
Translation
Sites of translation (sites of the synthesis of a polypeptide)
Ribosomes
In prokaryotes, which lack a nucleus, transcription and translation can occur:
Simultaneously
I’m eukaryotes, the mRNA is processed before it exits the _______ and enters the _______, where translation occurs.
Nucleus; cytoplasm
Initial RNA transcript of any gene
Primary transcript
In what 3 ways does RNA differ from DNA
- The sugar component is ribose, rather than deoxyribose
- Uracil (U) replaces thymine (T) as a nitrogenous base
- RNA is usually single stranded
Central dogma
DNA —> RNA —> protein
A sequence of 3 nucleotides provides how many possible unique sequences of nucleotides
4^3 or 64
The mRNA is _______ to the DNA template
Complimentary
What replaces thymine in mRNA?
Uracil
The nontemplate strand can also be known as the
Coding strand
Is sequence of codons read 3’ to 5’ or 5’ to 3’?
5’ to 3’
M. Nirenberg added artificial “poly U” mRNA to a test tube and obtained a polypeptide containing a _____ ____.
Amino acid
Stat codon
AUG
How many stop codons are there?
3
DNA sequence where RNA polymerase attaches and initiates transcription.
Promoter
Terminator
Sequence that signals the end of transcription
Bacteria have _____ type of RNA polymerase, but eukaryotes have _____.
1 ; 3
What RNA polymerase in eukaryotes synthesizes mRNA
RNA polymerase II
First step of transcription in Eukaryotes
Initiation : Transcription factors bind to the promoter and facilitate the binding of RNA polymerase II, forming a transcription initiation complex; RNA polymerase II separates DNA strands and transcription begins at the start point
Second key step of transcription in Eukaryotes
Elongation : RNA polymerase II moved along DNA strand, connecting RNA nucleotides that have paired to the DNA template to the 3’ end of the growing RNA strand
Third key step in transcription in Eukaryotes
Termination : After polymerase transcribes past a polyadenylation signal sequence, the pre-mRNA is cut and released
The promoter includes the transcription start point and recognition sequences, such as the ____ box
TATA
Transcription factors first have to recognize and bind to the promoter before RNA polymerase II can attach, at which point the assembly is called the
Transcription initiation complex
In prokaryotes, transcription ends after mRNA polymerase transcribes the ____ sequence.
Terminator
A string of adenine nucleotides
Poly-A tail
What end is the poly-A tail added to?
3’
What end is the cap added to?
5’
Long segments of non-coding nucleotide sequences
Introns
The coding regions (opposite of introns)
Exons
After a primary transcript is made of a gene, what is removed and what is joined together before the mRNA leaves the nucleus
Introns leave ; exons join together
The process of introns being removed and exons joining together
RNA splicing
Small RNA’s within a large protein complex
Spliceosome
What do spliceosomes do?
Snip an introns out of the transcript and connect the adjoining exons
RNA molecules that act as enzymes
Ribozymes
What 3 properties of RNA relate to its ability to function as an enzyme?
- RNA is single stranded and can base pair with itself forming a 3 D structure
- Some of its bases contain functional groups that can participate in catalysis
- It can hydrogen bond with other nucleic acid molecules, allowing it to precisely locate splicing regions
Alternative RNA splicing allows
Different polypeptides to be produced from a single gene
How does the mRNA that leaves the nucleus differ from pre-mRNA?
A 5’ cap with a modified guanine nucleotide is added to the 5’ UTR. A poly-A tail with up to 260 adenine nucleotides is attached to the 3’ UTR. Spliceosomes have cut out the introns and spliced the exons together
Transfer RNA (tRNA) molecules carry amino acids to
Ribosomes
Each tRNA has an anticodon that base pairs with a _____ codon on mRNA
Complimentary
Where is tRNA transcribed
The nucleus of a Eukaryote, then it moves into the cytoplasm
Each amino acid has a specific aminoacyl-tRNA synthetase that attaches it to its appropriate ____ molecules to create an aminoacyl tRNA
tRNA
Ribosomes consist of large and small subunits that are constructed in the
Nucleolus in Eukaryotes
What are the 3 tRNA binding sites
- P site : peptidyl; holds the tRNA carrying the growing polypeptide
- A site : aminoacyl; holds the tRNA carrying the amino acid to be added next
- E site : exit site; discharged tRNA’s leave the ribosome
What kind of RNA is primarily responsible for both the structure and function of a ribosome
tRNA
Initiation and elongation require energy from what
Hydrolysis of GTP
Name the 3 stop codons
UAA, UAG, UGA
Polypeptide synthesis begins in the
Cytoplasm
Mutations that are small scale
Point mutations
Types of small-scale mutations
- Nucleotide pair substitution : one nucleotide and its complementary partner is replaced with another pair of nucleotides.
- Silent mutations : a substitution that doesn’t change the amino acid translation
- Missense mutation : results in the imsertion of a different amino acid
- Nonsense mutation : occurs when a point mutation changes an amino acid codon into a stop codons
- Nucleotide pair insertions or deletions (frameshift mutations)
