DNA flashcards
Central dogma
DNA–mRNA–protein
mRNA can be ___
edited; spliced
- edits out INTRONS keeps EXONS
codons read in chunks of three
triplet code, provides more combinations
the genetic code
idea that proteins were made from specific sequences or amino acids
Features of the genetic code
1) continuity
- no spaces, punctuation, overlap
- knowing where to start is essential to establish the correct sequence “THE READING FRAME”
2) redundancy
- 64 codons, 20 amino acids
- 3 are STOP codons
- 1 start codon METHIONINE
- each amino acid has around 3 codons
3) Universality
- code is the same in all organisms EXCEPT MITOCHONDRIA and CHLOROPLAST
- established in the early history of life
- therefore, a gene from 1 organism can be taken and expressed in ANY other organism
example of redundancy
gene from bacteria that kills pests goes into corn to produce pest-resistant corn
Transcription
converts a gene into a single-stranded RNA molecule
- RNA carries DNA’s instructions
- central dogma
OBJECT: creating an accurate copy of a SMALL SECTION of a genome
Transcription results in 3 types of RNA, which are?
1) mRNA: carries the message that will be translated into a protein
2) rRNA: forms part of ribosomes where proteins are made
3) tRNA: brings amino acids from the cytoplasm to ribosome
initiation (transcription)
sense vs template strand
- the template strand is what is being transcribed (produce 5 to 3 from 3 to 5)
- the sense strand is used to tell you what each strand looks like
how many strands of DNA are needed/used to make a protein
1 strand, the other one is used for DNA replication
the TATA box
- binding site of RNA polymerase
- 2 promoter sequences signal a gene (diff sequences)
- genes start at the end of promoter 2
the promoter sequence does what
ID’s the correct strand and location
- tells us WHERE to start
- where transcription starts
(transcription) Elongation
- transcription is catalyzed by RNA polymerase
- RNA polymerase and other proteins form a transcription complex near the promoters
- the transcription complex recognize the start of a gene and unwinds a segment of it
termination (transcription)
- RNA polymerase hits terminator sequences
- mRNA separates from RNA polymerase which detaches from DNA
Difference of translation between prokaryotes and eukaryotes
prokaryotes: translation happens right after, no introns/nucleus for exportation
eukaryotes: processing of mRNA is needed before the translation is in a polypeptide chain (introns must be removed; editing)
processing (transcription, mRNA editing)
- 5’ methyl-cap and poly-a-tail is added to mRNA
5 leader sequence for translation
3 tail-end allows it to be used multiple times
intron splicing
- cut out introns with spliceosomes (snRPs)
- glue exons they want together
transcription is similar to replication
both are:
- complementary, anti-parallel, mRNA from 5 to 3, U instead of T
- transcription and replication both involve complex enzymes and complementary base pairings
- the two processes have different end results
REPLICATION COPISE ALL DNA TO MAKE 1 COPY
TRANSCRIPTION COPIES A GENE TO MAKE MANY COPIES
Protein synthesis: translation
objective: create an amino acid chain from a section of mRNA
- occurs in the cytoplasm
- an anticodon is a set of nucleotides that is COMPLEMENTARY to an mRNA codon (also anti-parallel)
- an anticodon is carried by tRNA
- if the anti-codon has INOSINE, its part of the wobble effect
inosine
wildcard codon that can match up with anything
activation enzymes
- responsible for attaching the proper a.a. to the proper tRNA
ribosomes
- different kinds of protein with rNA that consist of 2 subunits
- provide the site for protein synthesis in the cytoplasm bringing together the aa-tRNA and some enzyme
- each ribosome has a binding sites for the mRNA and 3 sites for the aa-tRNA complexes
translation steps
1) initiation
2) elongation
4) termination
initiation for translation
a sequence of the 5’ to 3’ end of the mRNA binds to a piece of RNA on the small subunit
elongation (translation)
- the aa-tRNA with the straight anti-codon attaches to P-site
the cyclical steps
1) translation starting
- 5’ end of mRNA bind to small section of ribosome
- tRNA binds to a start codon at P-site because of the codon anticodon match and this signals the rest of the ribosome of assemble
2) complementary trna BINDS to exposed codon and A-site bringing its a.a. closer to the first a.a. and breaks the bond
3) ribosome helps form a polypeptide bond between amino acids
4) ribosome moves along the mRNA strand the length of one codon, shifting the tRNA along (a-p-e)
5) empty RNA tRNA no molecule exits ribosome
6) complementary tRNA molecule binds to next exposed codons
7) RNA’s one through the the sites in order (a-p-e)
8) Once the stop codon is reached, the ribosome releases the point of protein and it disassembling
what are proteins build from
ribosome
terminator In translation
- once is the polypeptide chain detaches from the ribosome tRNA complex interactions such as H bonds abd disulphide bridges give the polypeptide chain its 3D structure
what is a gene composed of
- 2 promoters (TATA is common)
- 2 terminators
- introns and exons
- operon sequence, at times
enzymes will attach and be set up by _____?
promoters
RNA polymerase does what?
unzips and copies DNA
what factors are involved in transcription
1) DNA
2) transcription factors
3) RNA polymerase
4) ATP
@ the end, RNA polymerase disassociates and the strand is removed
transcription vs translation
- TRANSCRIPTION is copying
- TRANSLATING is conversion, where you convert mRNA to a polypeptide and occurs in the cytoplasm
gene control/expression
the method that cells use to control when genes are transcribed (copied)
how does the lacoperon work?
In the absence of lactose, a repressor protein binds to the operator region, preventing transcription of the lac genes.
When lactose is present, it acts as an inducer, binding to the repressor and allowing RNA polymerase to transcribe the lac genes, enabling the bacteria to utilize lactose for energy.
cells use what to ensure energy is spent wisely
feedback mechanisms that are used to regulate transcription
- regulate when genes are expressed
what is a feedback inhibition mechanism
- product of pathway blocking an enzyme at the start
operon model
- structural genes involved in the same process that are clustered together
- ends with a terminator sequence
- the promoter region contains the OPERATOR
(where the DNA segment allows for a gene to be transcribed, switches for genes to turn into proteins)
repressor proteins
- binds to the operator sequence
- blocks RNA polymerase from attaching to promoters
inducer
molecule attached to repressor protein and changes its shape so it falls off operator sequence
lacoperon
- has 3 genes that code proteins, enzymes that break down lactose
LACTOSE= inducer molecule=presence turns on genes
- binds to receptor to turn transcription on
inducible system
presence of a molecule allows for change to occurred repressor will bind to the operator sequence again, therefore proteins are only made when needed
trp Operon
- lac operon in reverse
- genes are ON until a molecule showed up, causes the repressor to bind to the operator to shut production down
trp gene off
tryptophan is present in high amounts, it binds to receptors and activates it
gene Ion
repressor protein is inactive
different sets of genes are…
expressed in various ways
- transcription is controlled by DNA sequence/protein transcription
- each gene was a combo of regulatory sequences
what is an allele
versions of a gene that are inherited for a certain characteristic and can be dominant or recessive
many times, the third base in a triplet isn’t as important, what is this caused by?
the wobble effect which uses inosine as a wildcard and provides flexibility for protections and mutations
what is transcription initiated by
the attachment of promoters
changes in genetic code can cause
differences in the amino acids present
function of a repressor
blocks RNA poly from sticking to promoters
a gene with an operator sequence
an operon
mutations
changes in the DNA that may/may not affect phenotype
(may not due to the wobble effect)
- occur randomly and spontaneously (arise from errors in replication)
induced mutations
can be forced by mutagens, direct cause involved
mutagen
anything that can cause a mutation
cancer
an accumulation of a series of mutations that don’t necessarily have to be the same
common causes of DNA damage
(replication issues)
- DNA mismatch
- single-strand break
- double strand break
- interstrand crosslinks
- (problems with bonding)
germ like mutations
heritable, germ line cells are those that happened in cells that become genetics
gametic mutations
occur in the gonads, contribute new alleles to gene pools (new version of a protein)
somatic mutations
occur in body tissues and aren’t passed on
occur in the testes of males and ovaries of females
heritable mutations can lead to changes
in the gene pool, where new mutations can either be: harmful, neutral, or advantageous
ex. albino alligator
harmful: easier to detect to predator, inability to camouflage, inability for temperature regulation
types of mutations
Point mutations involve changes in a single nucleotide base pair, either through substitution, insertion, or deletion,
chromosomal mutations affect larger segments of DNA, such as entire genes or chromosomes, resulting in alterations to the structure or number of chromosomes(inversion)
red sensing cones
helps us determine that without people being colourblind, we all perceive ,mutations differently
3 possible outcomes of mutations
1) silent: no charge in an amino acids sequence
2) beneficial
3) missense-new amino acid
5- early STOP action
3 values of mutations
1) beneficial, improves functioning or survival
2_ harmful: reduces fitness
3- silent : makes no shift during the time
what parts of a gene don’t show up in the polypeptide chain?
- promoter, terminator, operator sequence
the introns and exons do UNTIL the intron is edited out during mRNA editing by spliceosomes so ultimately the exons
not all mutations affect the phenotype, why?
due to the wobble effect: the presence of inosine where you only need the first two bases correct
what would happen if a mutation occurred to promoters or terminators
promoters: turns off genes permanently if you only mutate 1 because there has to be 2 promoters, creating the idea of pseudogenes
terminators: would never end (transcription) because nothing is telling it to stop, possibly a new amino acid
do promoters get transcribed from DNA to RNA
no, because transcription begins AFTER the promoter
do the 5’ methyl cap and poly-a-tail get transcribed
no
missense substitution
a single base is substituted for another base leaving a codon that codes for a different amino acid
nonsense substitution
some amino acids can be coded for by 4 or 6 different codons and are therefore less affected by substitutions
reading frame shift by insertion
single extra base is inserted into the DNA sequence, this displaces other bases and creates a new sequence of codons
can also lead to nonsense
reading frame shift by deletion
causing a frame shift, can lead to nonsense, deletion of base
partial reading frame shift
both an insertion and a deletion of bases within a gene can cause a frame shift effect where each codon no longer has the correct triplet of three bases
- there is no more biological activity if the amino acids altered are important to the functioning of the resulting proteins
reading frame shift
type of mutation that occurs when the normal grouping of codons are disrupted
chromosomal mutations
- deletion
- inversion
- translocation
- duplication
