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Chapter 15: Genes and Protein - Coggle Diagram
Chapter 15: Genes and Protein
Genes: a specific sequence of nucleotides on a strand of DNA that typically leads to the production of a specific protein product or an RNA molecule, which can lead to the development of a certain trait
Beadle and Tatum (1941)- hypothesized that each gene encodes for a single enzyme. Each gene would influence a specific step in a metabolic pathway.
Genes provide instructions for making proteins
Many genes encode for proteins other than enzymes. Proteins are needed that are NOT enzymes. Some genes encode for a subunit of a protein, make non-coding RNAs, etc. Many genes have more than one coding region
exons
and can be arranged in varying ways which will result in the development of different proteins
"alternative splicing
DNA->RNA->Protein... Transcription turns DNA into RNA and translation turns RNA into protein. DNA (ACGT) and RNA (ACGU)
Transcription: synthesis of
RNA
under the direction of
DNA
, produces
mRNA
and produces the template for translation. Translation: The synthesis of a
polypeptide
under the direction of an
mRNA
, occurs on
ribosomes
Genetic information is stored in a sequence 3 nucleotide portions called codons
Multiple codons can code for the same thing. There are
3
stop codons (UGA, UAA, UAG) and
1
start codon (AUG)
Genetic code is nearly universal.
almost all organisms use the same set of amino acids to build their proteins
Transcription
The synthesis of RNA under the direction of DNA, produces mRNA, and produces the template for translation
In
Prokaryotes
, transcription and translation are coupled. Newly made protein can quickly diffuse to its site of function
in
prokaryotes,
gene expression occurs solely in the cytoplasm so translation and transcription happen in the same place.
Prokaryotes
do not
require RNA transcript modification, meaning that RNA transcripts can be translated immediately after being transcribed.
A prokaryote's RNA transcript can be translated as transcription is progressing. Multiple polymerases can transcribe a single gene, numerous ribosomes can concurrently translate the mRNA, and this can allow for a specific transcript or protein to rapidly reach high concentrations.
initiation in prokaryotes
involves a promoter, transcription factors, and RNA polymerase.
Promoter
is a piece of DNA sequence that indicates where the RNA polymerase should bind and start.
Transcription factors
are proteins that aid in the initiation and regulation of transcription.
RNA polymerase
are proteins that synthesize the RNA transcript.
Elongation in prokaryotes
adds complimentary nucleotides to make mRNA. Tracks along the DNA template. It synthesis mRNA in the
5' to 3' direction
and unwinds and rewinds as the DNA is read. Occurs at a rate of 40 nucleotides per second
Termination in prokaryotes
: Rho proteins travel along mRNA and interact with RNA polymerase terminating transcription.
Rho independent termination
forms of an mRNA hair-pin when GC rich region is reached, then followed by A rich residues, then terminates transcription
In
Eukaryotes
, transcription occurs in the
nucleus
and translation occurs in the
cytoplasm
. RNA processing where pre-mRNA is processed into functionally active mRNA.
Initiation in Eukaryotes
involves a promoter (TATA box), transcription factors (TFII(A-J), and RNA polymerase (RNA polymerase II).
Transcription factors
recognize the promoter. and
RNA polymerase II
binds and forms the transcription initiation complex.
RNA Polymerase I
transcribes rRNA genes,
RNA Polymerase II
transcribes protein-coding genes, and
RNA polymerase III
transcribes rRNA, tRNA, and small nuclear RNA genes
Elongation in Eukaryotes
is facilitated by the FACT complex (facilitates chromatin transcription). It removes and reassembles the nucleosomes as polymerase synthesizes the mRNA.
Eukaryotic termination
is different for different polymerases.
Polymerase II
transcribes 1000-2000 nucleotides excess of the gene template which are removed during mRNA processing.
RNA Polymerase I
requires a termination protein that recognizes a specific 18 nucleotide sequence.
RNA polymerase III
terminates transcription via hairpin formation.
After termination, the RNA needs additional processing
Post-transcriptional processing
: Eukaryote cells must modify RNA after transcription & before translation. Enzymes in the eukaryotic nucleus must modify pre-mRNA in specific ways.
Add a 5' methylguanosine cap
and
3' poly-A tail
and
intron splicing
(removal of non-coding introns)
Pre-mRNA splicing
involves removal of introns from primary RNA transcript. Catalyzed by complexes called
spliceosomes that are composed of proteins and RNA molecules
snRNA+protein=snRNP
Alternative splicing
introns allows for alternative RNA splicing. Protein domains can correspond to specific exons
There are
3 steps
in transcription: initiation, elongation, and termination
Translation
Polypeptides are formed when the amino group forms a peptide bond with the carboxyl group of another amino acid.
Catalyzed by ribosomes
Components in translation: tRNA, ribosomes, mRNA, and polypeptides
tRNA
all have a specific amino acid on one end and have an anticodon on the other. Single RNA is about 80 nucleotides long. Use specific
Aminoacyl-tRNA synthetase
to attach its amino group
Ribosomes
are proteins and rRNA complexes that facilitate mRNA and the production of the corresponding polypeptide. Achieved through pairing of
mRNA codons and tRNA anticodons
contains 2 ribosomal subunits and has three binding sites for tRNA
Initiation
: mRNA attaches to the smaller subunit of the ribosome, AUG is the start codon tRNA with anticodon attaches, the larger subunit of ribosome comes in
Elongation
: tRNA move in with the appropriate amino acid, the chain grows using peptidyl transferase
Termination
: stop codon is reached, chain is processed but
in eukaryotes, the chain moves into the endoplasmic reticulum to be processed further
After translation, polypeptides may undergo modifications via the endomembrane system, affecting the 3D shape, occurring the endoplasmic reticulum
Mutations
- a change in the genetic material
Point mutations, frameshift mutations, chromosomal mutations
Substitutions
- replacement of 1 base pair with another.
Silent
- the single base pair change but do not cause an amino acid change
Missense
:causes change in amino acid, can be detrimental or unnoticed
Nonsense
: change turns something from an amino acid to a stop codon
Insertions and Deletions
: insertion is adding 1 base pair, deletion is removing 1 base pair within the genome, shifts the entire protein message
Mutagens
- physical or chemical agents that cause mutations
Spontaneous mutations
- can occur during DNA replication, recombination, or repair