Flashcards in Exam 3 Deck (93):
Does a mutation have to be inherited?
What is a somatic mutation?
A mutation in a non-reproductive cell
What does a somatic mutation do?
It generates a mosaic because some cells have the mutation and some don't. Only descendants of the original mutation carry the mutation
What is a germline mutation?
A mutation in reproductive cells. The parent does not show a mutation but the offspring either show or do not show mutation
What is a codon?
3 nucleotide sequence that codes for a specific amino acid
What is a reading frame?
The series of codons that code for amino acids, starts at the start codon (AUG) that codes for Met
What is a transition mutation?
Mutation that changes pyrimidine to pyrimidine or purine to purine
What is a transversion mutation?
A mutation that changes purine (A/G) to pyrimidine (T (U)/C or vice-versa
What is a missense mutation?
A mutation that results in a different amino acid. This may or may not effect the phenotype
What is a nonsense mutation?
A mutation that results in a stop codon. Results in translation ending prematurely, severe phenotype effect
What is a silent mutation?
A mutation that does not alter the amino acid sequence, it has no phenotype effect
What is a forward mutation?
A mutation that alters the wild-type phenotype, a new mutation
What is a reverse mutation?
A mutation that reverses a forward mutation to go back to the wild-type. This is very rare.
What is a suppressor mutation?
2 different mutations occur on different genes. The combination of the two mutations causes the phenotype to go back to the original. This is for intergenic
What about a intragenic suppressor mutation?
The 2 mutations that reverse the first mutation occur at different sites on the same gene
What are the 3 main causes of mutation?
1) DNA replication errors, 2) DNA damage after replication, 3) Transposons or viral insertions after replication
How do DNA replication errors work?
If all of the review techniques do not catch the mutation, the mutation is fixed. This occurs during replication. This could be with point mutations or expanding trinucleotide repeats where mispairing occurs and extra repeats are formed
What happens in tautomeric shifts?
A proton shifts and the base is converted from the common form to the rare form. This causes incorrect base pairing. The base usually shifts back but the mutation is already recorded.
What happens with base analogs?
Chemicals with structures similar to bases can get ionized and pair wrong to cause a mutation
What happens with chemically induced mutations?
Mutagenic agents modify bases and cause misspairing
What happens in radiation induced mutations (X-rays, gamma rays, cosmic rays)
The radiation causes DNA damage either by altering the structure of bases, breaking bonds, and introducing double stranded DNA breaks
What happens with UV radiation caused mutation
This causes thymine dimers which distort the DNA and block replication.
What is a transposon?
Mobile genetic information that moves semi-autonomously and inserts randomly into the genome
What is the general structure of transposons?
A middle, inverted repeats
What is replicative transposition?
copy and paste, the transposon replicates itself and the 2nd copy inserts into the genome
What is non-replicative transposition?
cut and paste, the original transposon cuts itself out and inserts into genome
What is retrotransposition?
It is where a transposon is transcribed to RNA and then reverse transcriptase turns the RNA to DNA and a 2nd DNA strand is synthesized then the full transposon now double stranded is inserted in the genome
What are the 2 types of mutagenic effects of transposons?
Gene disruption and chromosome rearrangement
What happens with gene disruption and what is an example of this?
The transposon inserts and disrupts gene. Color in grapes- black without transposon, green with transposition, red with partial removal of transposon
What happens with chromosome rearrangement?
2 transposons insert and they pair during mitosis, they cause a deletion or a duplication
What are the 3 types of bacterial transposons?
Insertion sequence, composite, and non-composite
What is an insertion sequence transposon?
The simplest bacterial transposon that only has an insertion sequence and info for movement
What is a composite transposon?
A transposon made up of 2 insertion sequences that can mobilize independently or together, when they move together they can carry the gene between the insertion sequences with them.
What is the non-composite transposon?
A transposon that doesn't require an insertion sequence. It is just many genes and transposase. The most complex
What are the 2 types of eukaryotic transposons?
Ac=fully functional, Ds=fractured not fully functional can not move without Ac provided transposase
How does variegation happen?
Ac causes Ds to go into gene and disrupt gene. Then Ds is removed at some point during development causing pigmentation. Depending on which point during development Ds is removed, amount of pigmentation is different
What are the 3 hypothesis of evolution of transposons?
Cellular function hypothesis. genetic variation hypothesis, and selfish gene hypothesis
What does the cellular function hypothesis say?
That transposons have a symbiotic relationship with the cell, they have a valuable function
What does the genetic variation hypothesis say?
Transposons exist to introduce genetic variability
What does the selfish gene hypothesis say?
Transposons are just like viruses that have no purpose just to replicate themselves and insert themselves into the genome like parasites
What is differential gene expression?
The process that determines which genes are translated under which conditions
What are the 3 differences between the structure of DNA and RNA
RNA is single-stranded, has uracil instead of thymine, and has a 2' OH instead of a H
What is the secondary structure of RNA?
It makes a double strand by folding on itself and making hairpins.
Why is the secondary structure like this for RNA and not DNA?
DNA is double stranded and RNA is single stranded
What is the function of mRNA?
mRNA is the coding sequence for proteins
What is the function of rRNA?
rRNA is non-coding, it makes up the ribosome
What is the function of snRNA?
It makes up the spliceosome
What is the function of miRNA?
It regulates transcription
What is the function of siRNA?
It degrades the target mRNA
Which DNA strand is used as the template?
The DNA strand with the promoter is used as the template strand
Relative to the template strand, which direction does transcription occur?
5' to 3'
Can units of transcription overlap?
What are the 3 components of a transcriptional unit?
A promoter, a RNA coding region, and a terminator
What are the 2 key elements associated with the bacterial promoter?
The Pribnow box at -10 and the TTGACA at -35
What enzyme complex recognizes the Pribnow box and TTAGACA
The holoenzyme, which is the RNA complex with the sigma complex
What role does the sigma factor play in the function of the bacterial RNA polymerase.
The sigma factor binds and initiates transcription. Without the sigma factor, transcription would start randomly without the promoter
What are the differences between prokaryotic and eukaryotic transcription
Prokaryotes have a transcription factor instead of promoter, a TATA box instead of Pribnow, a sigma factor that falls off in prokaryotes.
How many RNA polymerases are present in most eukaryotes?
WHat RNA polymerase transcribes mRNA?
What is the difference between the core promoter and the regulatory promoter?
The core promoter is used for basal, the regulatory promoter is used for enhanced. The regulatory promoter is upstream from the core promoter
Do eukaryotes have sigma like proteins?
TF2 binds to the TATA box but doesn't fall off. General transcription factors replace the sigma factor
What is the difference between eukaryotic and prokaryotic termination?
Rat cleaves without a loop and degrades, Rho forms a loop and cleaves off. Eukaryotic has cap and tail
What is a cistron?
A cistron is a section of DNA or RNA that codes for a specific polypeptide
What are UTRS
untranslated regions that have regulatory functions
What is the coding sequence?
The area from start to stop that codes for proteins
What is the 5' cap?
It is a modified guanine that increases stability, involved in the initiation of translation and is involved in the export from the nucleus, prokaryotic mRNAs are not capped
What is the poly(A) tail?
It is a series of adenine nucleotides that is at the end of eukaryotic mRNA. It is involved with mRNA stability, regulation of mRNA translation, and export from the nucleus
What are introns?
What are exons
What 3 sequences are required for splicing of eukaryotic mRNA?
The 5' splice site, branch point, and 3' splice site
What is the spliceosome?
A large 5 snRNP complex that splices out introns
What is the basic structure of an amino acid?
a carboxyl, amino group, hydrogen, and radical side chain
What varies between amino acids?
The radical side chain
Which type of bond is formed between amino acids in a protein
Describe the 4 levels of structural organization in proteins
Primary= amino acid sequence, Secondary= initial interaction within the same strand, Tertiary= add foldings to the initial interactions, Quarternary= interaction between multiple amino acid chains
Translation is degenerate. What does that mean?
Multiple different codons can code for the same amino acid
As it relates to the genetic code, what is wobble?
Wobble is when the first 2 positions must pair perfectly but the 3rd position is flexible. If the first 2 positions are the same, it codes for the same amino acid (is synonymous)
What is a reading frame?
The amino acid coding sequence that starts with AUG that codes for Met
Is translation overlapping and how is it established?
Translation is never overlapping and is established by a start and a stop codon
What are the 2 steps in proofreading used by the ribosome to select the correct tRNA
One is rRNA proofreading through H-bonding and the other is proofreading that places strain.
How does the rRNA proofreading the H-bonding work?
incorrectly paired tRNAs at 1 or 2 are kicked out
How does the 16s proofreading place strain
The correct pairing fits perfectly and if it is not correctly paired, too much strain is applied and the pairing can not withstand it
What are the 4 major stages of translation?
1)tRNA charging, 2) Initiation, 3) Elongation, 4) Termination
What happens during tRNA charging?
amino acids are added to the tRNA at the acceptor stem
What happens during initiation of translation?
The ribosome binds to the start codon with an initiator tRNA
What happens during the elongation step of translation?
Amino acids are linked to the growing polypeptide chain
What happens during the termination step of translation
the ribosome reaches the stop codon and the polypeptide chain is released
What is mRNA surveillance?
It is mRNA and polypeptide quality control
What are the 3 types of mRNA surveillance
1) Nonsense-mediated, 2) Non-stop decay, 3)No-go decay
What is nonsense-mediated mRNA surveillance/
It identifies pre-mature stop codon and degrades the mRNA before translation can occur
What is non-stop decay?
the protein and mRNA are degraded when the ribosome translates into the poly(A) chain
What is no-go decay?
The ribosome stalls on the secondary and the protein is targeted for degradation