What is different about RNA polymerases in respect to DNA polymerases?
RNA polymerases DO NOT need primers
What are the 3 phases of transcription
Initiation, elongation, and termination
What does initiation require and what does it tell you
It requires a promoter that tells you WHERE to start and WHICH STRAND to transcribe
What happens in Elongation?
RNA unwinds DNA 13 BASE PAIRS AT A TIME, READS TEMPLATE 3-TO-5, ADDS NUCLEOTIDES TO 3, the first nucleotide in the NEW RNA is its 5 end. RNA polymerase can proofread but it allows more mistakes
What happens in Termination
A specific DNA base sequence is required. Sometimes, the transcript needs a helper protein and other times it falls away from dNA template and RNA polymerase.
What are coding regions?
Sequences of DNA molecules that are expressed as proteins.
What are 2 types of coding regions?
Introns (intervening regions) and exons (expressed regions)
What are introns
What are exons
Where do Introns and Exons appear?
In the primary mRNA transcript- pre-mRNA. And introns are removed from the final mRNA.
What is nucleic acid hybridization
It reveals introns. The target DNA is denatured and incubated with a probe (nucleic strand) and they join creating hybrid strand. (strand and a half)
What do introns do
They interrupt but do not scramble the DNA sequence that encodes a polypeptide
What can separated exons do
They can code for different domains of the protein
What does the spliceosome do
Its a protein complex that cuts of pre-mRNA, releases introns and splices the exons together to produce the mature mRNA ready to go on to the next protein making step
What happens in B-thalassemia
The pre-mRNA can not be spliced correctly.
What does alternative splicing result in
Different mRNAs and different polypeptides from a single gene
What does the genetic code do
It specifies WHICH amino acid will be used to build a protein
What is a codon
It is a sequence of 3 bases, each specifying a particular amino acid
What is the universal START codon
AUG- initiation signal for translation
What are the stop Codons-
UAA, UAG, UGA. They stop translation and the polypeptide is released.
What is a redundant genetic code
When there is more than one codon for a particular amino acid
Why are genetic codes not ambiguous
Each codon specifies only one amino acid
What is meant by genetic code is universal
The condons all specify the same amino acids in all organisms.
What are some exceptions the the universal genetic code idea
Mitochondria, protists, and chloroplasts
How can mutations be defined
In terms of their effects on polypeptide sequences.
What are silent mutations
Mutations that have no effect on amino acids. They are found in noncoding regions of DNa
How do base substitutions affect amino acid sequence
SOMETIMES they affect the sequence, sometimes they dont and it may be repaired.
What is missense mutation
There are substitutions by ONE amino acid for another protein.
What can be a result of missense mutations
A defective protein or reduced protein efficiency or even gain of function
What is nonsense mutation
STOP that nonsense. A base substitution causes a STOP CODON somewhere in the mRNA so it is stopped prematurely. So much so that it may not even have a function
What is a frameshift mutation?
Insertions or deletions of bases in DNA, leaving an extra nonfunctional protein. Poor A is all alone :(
What does tRNA do to mRNA
It links info in the codons with specific amino acids.
For each amino acid, there is a ____ of tRNA
Specific type or species
In what ways can we ensure the protein made is the one specified by mRNA?
tRNA must read mRNA codons correctly & tRNAs must deliver amino acids corresponding to each codon.
What are the 3 functions of tRNA
Bind to amino acid and charge it, bind to their midpoint-anticodon-to mRNA molecules & interact with ribosomes.
What does wobble do
When the codon is not specified for the base at the d end, the wobble allows each cell to produce fewer tRNA species without making the genetic code ambiguous but specific
What charges the tRNA with amino acids
Aminoacyl-tRNA synthases; activating enzymes
What is the amino acid to tRNA ratio?
Which would be recoginized? Amino acid or tRNA in protein synthesis?
Protein synthesis machinery recognizes anticodon, not amino acid
Where does translation of mRNA by RNA happen?
At the workbench: the ribosome. It holds mRNA and charged tRNAs in correct position to allow assy of polypeptide chain.
Are ribosomes specific?
No! they can make ANY type of protein!!
3 binding sites in the large subunit.
A, P, and E
The A site
Amino site, binds with anticodon of charged tRNA
The P site
Polypeptide site; tRNA adds amino acid to growing chain
Site where tRNA sits before being released from ribosome
What are 3 steps of translation?
Initiation, elongation, and termination
What is initiation in transcription?
Charged tRNA and small ribosomal subunit bound to mRNA make up an initiation complex. The small subunit moves along mRNA until they get to the start codon, AUG. first amino acid Is ALWAYS methionine. The large subunit joins complex and charge tRNA is now at the P site
What happens during elongation in transcription
Second charged tRNA enters A site, large subunit (hand) catalyzes two reactions (breaks bond between tRNA in P site and ITS amino acid. A Peptide bond forms between amino acid and amino acid on tRNA in the A site.
How do we get from elongation to termination in transcription?
The first tRNA has released its methionine and it moves to the E site and leaves ribosome where it can be charged again. This happens again and again.
What is peptidyl transferase activity?
It is something the large subunit has. If rRNA is destroyed, the activity stops.
What happens during termination in transcription
Translation ends with a stop codon enters A site. It binds a protein release factor and allows for hydrolysis between polypeptide chain and tRNA on P site. Chain separates from ribosome & c terminus is last Amino acid added.
What is a polyribosome (polysome)
A strand of mRNA with associated ribosomes
What are two posttranslational askects of protein synthesis
Polypeptide emerges from ribosome and gets into 3d shape. Its conformation lets it interact with others. It may contain a signal sequence that lets you know wherein the cell it belongs
What happens when there is no signal sequence?
The protein will stay where it was made.
How do signal sequences work?
They bind to a receptor protein on the organelle surface, a channel is formed and the protein moves into the organelle.
What are some types of protein modifications?
Proteolosys, glycosylation, phosphorylation
What is proteolysis
Cutting of a long polypeptide chain into final products by proteases
What is glycosylation
Addition of carbohydrates to form glycoproteins
What is phosphorylation
Addition of phosphate groups catalyzed by protein kinases.
What are protein kinases
Charged phosphate groups that change the conformation of the protein
How do antibacterials target bacterial protein synthesis?
They kill bacteria by interrupting translation. They bind to small subunit of ribosome which changes its structure and then the poor charged tRNA cant bind to A site :(