Genes Flashcards
How WAS gene described?
A unit of DNA which performs one function.
Usually equated with the production of one RNA or protein
In order to provide useful function, a gene needs to be:
Expressed
Regulated
How is the information in DNA converted into functional proteins?
“central dogma” = DNA stores information, RNA reads, decodes and uses that information to make proteins via ribosomes
What forms does RNA have?
Messenger - mRNA
Transfer - tRNA
Ribosomal - rRNA
Small nuclear – snRNA
MicroRNA – miRNA
How many different codons are possible?
How many are stop codons?
How many amino acids can be coded for?
64 possible different codons
3 = ‘stop’ codons
remaining 61 specify 20 different amino acids
THE GENETIC CODE IS ‘REDUNDANT’ OR ‘DEGENERATE’
position 1 = most conserved,
position 3 = least conserved
Mutational changes can then by SYNONYMOUS (no change to the amino acid produced) or NON-SYNONYMOUS (changing the amino acid produced)
What do you start and end a gene sequence with?
A promoter region, the start codons and finally a stop codon and a terminator region
What are non-coding sequences called?
introns
What is the purpose for the promoter and terminator regions and what’s the result?
Promotor sequences tell the RNA polymerase where to start, terminator where to finish.
Resulting in a primary mRNA transcript finally ‘edited’ and introns removed.
What do the start and stop codons code for?
A ‘start’ codon is often methionine, AUG and a ‘stop’ codon doesn’t code for an amino acid (UAA, UGA or UAG).
When are promoters, terminators, start and stop codons used?
Promoters and terminators are used during transcription
Start and stop codons are used during translation
What are the differences between archaea and eukarya?
EUBACTERIA/ARCHAEA
*rigid outer cell wall
single cellular compartment
single circular chromosome set of linear chromosomes attached to the cell wall
*transcribed mRNA is translated in nucleus directly into proteins
Eukarya
*Internal cytoskeleton
*complex set of internal membranes subdivide cell into micro- environments specialised for particular functions.
*Set of linear chromosomes located within a nuclear membrane
*transcription in nucleus, translation in cytoplasm
What are operons and where are they found
They are found in eubacteria and archaea.
They are ‘strings’ of genes that code for products that are all required as part of a chemical pathway. Each operon is regulated by one single promoter and operator mechanism. Whether the operon is transcribed or not depends on whether a repressor (encoded by a nearby gene) is bound to the operator region or not.
Give an example of an operon and how it works in simple terms.
e.g. the operon for lactose metabolism is the ‘lac operon’
When lactose is absent
– pathway blocked, no transcription of DNA
When lactose is present
– pathway open, DNA can be transcribed
Gene regulation in Eubacteria/Archaea occurs at the transcription level
How are genes regulated in eukarya?
Physical structure of the DNA
Transcription regulation
- initiation (transcription factors)
- processing and modification (speed of this)
mRNA transport (speed)
- the rate that mRNA leaves the nucleus.
mRNA stability
- ‘degrading signals’
Translational control
- mRNA recognition
Posttranslational control
- protein modification
Protein transport & stability
What is evolutionary novelty driven by?
Evolutionary novelty may be usually driven by differences in the timing and duration of gene activation, as opposed to gene function itself.
