Chapter 7: RNA and the Genetic Code Flashcards
What are interferons?
What do they do?
Interferons interfere with viral replication.
They do so by curtailing the process of transcription and translation.
Briefly walk through the process of expressing genetic information.
The first step in expressing genetic information is transcription of the information in the base sequence of double straight DNA molecule to form a single strand molecule of RNA.
The second step is translating that nucleotide sequence into a protein.
What is the central dogma of molecular biology?
We have DNA. DNA contains genes. DNA is transcripted to RNA. RNA can be reverse transcribed to DNA. RNA is translated to proteins.
Which way is mRNA synthesized, which directionality does it have relating to DNA.
Which way do ribosomes translate the mRNA? Why?
mRNA is synthesized in the 5’-3’ direction and is complimentary and antiparallel to the DNA template strand (RNA transcriptase READS in the 3’-5’ direction)
The ribosome translates the mRNA in the 5’-3’ direction, as it synthesize as the protein from the amino terminus (N) to the carboxy terminus (C).
There are three types of RNA. What are they?
mRNA: messenger RNA carries information, specifying the amino acid sequence of the protein to the ribosome.
tRNA: transfer RNA is responsible for converting the language of nucleic acids to the language of amino acids and peptides.
rRNA: ribosomal RNA is synthesized in the nucleus and functions as an integral part of the ribosomal machine machinery used during protein assembly in the cytoplasm.
What is mRNA?
What enzyme transcribes mRNA?
What is a codon?
What is monocistronic, polycistronic?
mRNA is the messenger of genetic information. mRNA takes the information from the DNA to the ribosomes, where creation of the primary protein structure occurs. mRNA is the only type of RNA that contains information that is translated into protein.
RNA polymerase transcribes mRNA from DNA.
A codon is a three nucleotide segment that codes for an amino acid.
Monocistronic (eukaryotic mRNA): each mRNA molecule translates into only one protein product.
Polycistronic: (prokaryotic mRNA): mRNA can result in different proteins by starting the process of translation at different locations in the mRNA.
What is tRNA?
What is aminoacyl-tRNA synthase?
Where does the AA attach to the tRNA molecule?
What is rRNA?
What are ribozymes?
Ribosomes are enzymes made of RNA molecules rather than peptides.
What is a codon?
How many codons are there?
Which way are codons written? Why?
Consists of three bases that code for a specific AA.
There are 64 codons, 61 for one of the 20 AA, 3 for encoding for the termination of translation.
Codons are written in the 5’-3’ direction because that’s the way the DNA is structured.
Speak to the antiparallel nature of tRNA anticodon and codon on mRNA.
Every preprocessed eukaryotic protein starts with the exact same AA. That AA is what?
What is the start codon for that AA?
What are the stop codons?
Every eukaryotic protein starts with methionine Met M, codon for methionine is AUG and is considered the start codon.
The three stop codon are UGA, UAA, and UAG.
Mnemonic for remembering the stop codons.
What two AA only have one codon?
Methionine Met M
Tryptophan Trp W
What is the wobble position of a codon?
What is wobble?
Bring it all together.
The genetic code is degenerate because more than one codon can specify a single amino acid.
For the 18 amino acids that have multiple codons, the first two bases are the same. The third base is variable and is referred to as the wobble position.
Wobble is an evolutionary development designed to protect against mutations in the coding regions of our DNA.
Mutations in the wobble position tend to be called silent or degenerate, which means there is no effect on the expression of the amino acid, and therefore no adverse effects on the polypeptide sequence.
What is a point mutation?
If a mutation occurs, and it affects one of the nucleotides in a codon, it is known as a point mutation.
Point mutations can affect the primary amino acid sequence of the protein and are called expressed mutations. There are two categories of expressed mutations. What are they?
Missense mutation: mutation where one amino acid substitute for another.
Nonsense mutation: mutation were the codon now encodes for a premature stop codon (aka truncation mutation).
What is a missense mutation? Nonsense?
Missense: incorrect AA
Nonsense: premature stop codon
What is a frameshift mutation?
The three nucleotides of a codon referred to as the reading frame.
Frameshift mutation occurs when some number of nucleotides are added to or deleted from the mRNA sequence.
Caused by insertion or deletion of nucleotides.
What is cystic fibrosis?
Cystic fibrosis is caused by a frameshift mutation: a deletion at codon 508 in the polypeptide chain of the CFTR (Cystic Fibrosis Transmembrane Conductance Regulator (CFTR) Gene) chloride channel gate.
The loss of phenylalanine residue at this position results in defective chloride ion channels, leading to blocked passage of salt and water into and out of cells.
This causes abnormally thick sticky mucus in cells that line the passageway of the lungs and pancreas and other organs.
The sticky mucus traps bacteria in increasing the likelihood of infection in patients.
MCAT concept check the genetic code 7.1 page 256 question 1
What are the roles of the three main types of RNA?
mRNA carries information from DNA by traveling from the nucleus (where it is transcribed) to the cytoplasm (where it is translated).
tRNA translates nucleic acids to amino acids by pairing its anticodon with mRNA codons, it is charged with an amino acid which can be added to the growing peptide chain.
rRNA forms much of the structural and catalytic components of the ribosome, and act as a ribozyme to create peptide bonds between amino acids.
MCAT concept check the genetic code 7.1 page 256 question 2
Write out the sequence from 5’-3’. Then write the mRNA sequence antiparallel (3’-5’). The reverse of this will be the sequence of the mRNA, or the codon, that translates to an AA.
MCAT concept check the genetic code 7.1 page 256 question 3
MCAT concept check the genetic code 7.1 page 256 question 4
What is wobble? What role does it serve?
Wobble refers to the fact that the third base in a codon often plays no role in determining which amino acid is translated from that codon.
For example, any codon starting with CC codes for proline, regardless of which base is in the third position (the wobble position)
This is protective because of mutations in the wobble position will not have any effect on the protein translated from that gene.
MCAT concept check the genetic code 7.1 page 256 question 5
What is transcription?
The creation of mRNA from DNA is known as transcription.
DNA cannot leave the nucleus as it will be quickly degraded. So mRNA is used.
Talk about transcription.
Helicase. Topoisomerase. Template strand (antisense strand).
Transcription produces a copy of only one of the two strands of DNA.
Helicase and topoisomerase unwind and keep the DNA from supercoiling, allowing the machinery to access the gene of interest in the DNA.
Transcription results in a single strand of mRNA, synthesized from the template or antisense strand. The mRNA strand is both complimentary and antiparallel to the DNA template strand.
What enzyme synthesizes RNA in eukaryotes?
How do these enzymes find the region of interest?
RNA is synthesized by DNA dependent RNA polymerase.
In eukaryotes, RNA polymerase II is the main one. It contains a TATA box, known for its high concentration of adenine and thymosine, which binds to promoter regions. (RNA polymerase I: rRNA; RNA polymerase III: tRNA and rRNA)
RNA polymerase locates regions of interest through transcription factors and promoter regions.
Do RNA polymerases require primers to begin generating a transcript?
No.
Unlike DNA polymerase, which requires a primer region, RNA polymerase does not require a primer.
In eukaryotes, there are three types of RNA polymerases. Name them and what they do.
In which direction does RNA polymerase travel along the template strand?
RNA polymerase revels along the strand in the 3’-5’ direction, which allows for the construction of transcribed mRNA in the 5’-3’ direction.
Is there editing involved in transcribing of mRNA?
Unlike DNA polymerase, RNA polymerase, does not proofread its work, so the synthesis transcript will not be edited.
What is the coding strand, or sense strand, of DNA?
Can we determine the identity of the mRNA stand transcribed from the antisense or template strand?
The coding strand of DNA is not used as a template during transcription.
Because the coding strand is also complementary to the template strand, it is identical to the mRNA transcript save for uracil replacing thymine in RNA.
A numbering system is used to identify the location of important bases in the DNA strand. How so?
What region will we find the TATA box (where RNA polymerase binds)?
Are any of them labeled 0?
The first base transcribed from DNA to RNA is defined as the +1 base.
Bases to the left of the starting point (upstream toward the 5’ end) are given negative numbers.
Basis to the right of the starting point (downstream toward the 3’ end).
The TATA box, where the RNA polymerase binds is around -25.
No nucleotide in the gene is numbered zero.
When will transcription discontinue?
What is the product of transcription?
When RNA polymerase reaches a termination sequence or stop signal, transcription will discontinue.
The product of transcription is termed heterogenous nuclear RNA (hnRNA). hnRNA will be posttranscriptionally modified to mRNA.
What is hnRNA?
hnRNA is heterogenous nuclear RNA and is the precursor for mRNA.
hnRNA (heterogenous nuclear RNA) gets posttranscriptionally modified to mRNA.
What is posttranscriptional modification?
What three things happen during posttranscriptional modification?
What are the reactants and products of posttranscriptional modification?
hnRNA must undergo three specific processes before it can leave the nucleus and interact with the ribosome. Modifications are required to survive the conditions of the cytoplasm.
The three things that happen are:
Intron/Exon splicing
5’ cap
3’ poly tail
heterogenous nuclear RNA (hnRNA) is posttranscriptionally modified to mRNA.
What three things happen during posttranscriptional modification?
The three things that happen are:
Intron/Exon splicing
5’ cap
3’ poly tail
Describe intron and exon splicing.
What is a spliceosome? What are snurps (snRNPs)
hnRNA must have introns (noncoding) excised and exons (coding) spliced.
Spliceosomes splice together exons in hnRNa.
In the spliceosome, small nuclear RNA (snRNA) and small nuclear ribonucleoproteins (snRNP or snurps) splice sites of the introns. The non coding regions are excised in the form of a lariat and then degraded.
What is the snRNA snRNP complex?
The small nuclear RNA and small nuclear ribonucleoprotein complex (snRNA/snRNP) complex regained the 3’ and 5’ splice sites of the introns and excise the introns for degradation.
What is the 5’ cap?
It serves two purposes. What are they?
At the 5’ end of the hnRNA molecule, a 7-methylguanylate triphosphate cap is added.
This is recognized by the ribosome as the binding site.
It also protects the mRNA from degradation.
What is the 3’ poly tail?
What is it composed of?
It serves two purposes. What are they?
The 3’ tail is a polyadenosyl tail (poly-A) and protects the 3’ end from degradation.
It is composed of adenine bases.
The 3’ poly tail:
Assist with the export of the mature mRNA to the cytoplasm.
Works as a fuse. The longer the poly a tail, the longer it will last before degradation in the cytoplasm.
What is alternative splicing?
The primary transcript of heterogenous nuclear RNA (hnRNA) may be spliced together in different ways to produce multiple variants of proteins and coded by the same original gene.
This is referred to as alternative splicing.
MCAT concept check 7.2 transcription page 262 question 1
MCAT concept check 7.2 transcription page 262 question 2
When starting transcription, where does RNA polymerase bind?
RNA polymerase II binds to the TATA box, which is located in the promoter region of a relevant gene at about -25.
MCAT concept check 7.2 transcription page 262 question 3
Poly a tail
5’ end
Intron/exon splicing
MCAT concept check 7.2 transcription page 262 question 4
What is alternative splicing, and what does it accomplish?
Alternative splicing is the ability of some genes to use various combinations of exons to create multiple proteins from one hnRNA transcript.
This increases protein diversity and allows the species to maximize the number of proteins it can create from a limited number of genes.
Alternative splicing makes different isoforms of exons and proteins.
What is translation?
Where does it happen?
How does it get there?
Translation is the converting of the mRNA transcription into a functional protein.
Translation happens in the cytoplasm.
Once the mRNA transcript is created and processed, it exits through the nucleus through nuclear pores.
Which direction do the following read:
Replication
Transcription
Translation
What is the ribosome?
What are the three binding sites of the ribosome?
What are the subunits of the ribosome? Are they always together?
The ribosome is composed of proteins and rRNA. The ribosome are the enzymes that catalyze translation.
The three binding sites of the ribosome are:
A (aminoacyl)
P (peptidyl)
E (exit)
There are large and small subunits that only bind together during protein synthesis.
Where are the genes that transcribes ribosomal RNA?
What enzyme transcribes rRNA?
The genes that transcribe ribosomal RNA are located in the nucleolus. This is what differentiates the nucleolus from the nucleus. Although they contain the same DNA, the nucleolus is the site of transcription of rRNA.
RNA polymerase I transcribes most of the rRNA, RNA polymerase III does some rRNA but mostly tRNA.
Ribosomal proteins along with rRNA create a mature ribosome. Do the understand on the subunits.
Is it noteworthy that prokaryotic ribosomes and eukaryotic ribosomes differ from each other?
The difference between eukaryotic and prokaryotic ribosomes allows us to target antibiotics such as:
Macrolides like azithromycin and erythromycin
Tetracycline (doxycycline)
Vancomycin
How do prokaryotic and eukaryotic ribosomes differ?
Eukaryotic ribosomes are larger and contain different combinations of rRNA subunits.
What are the three stages of translation?
Along with the factors, what else is required for translation?
Initiation (using initiation factors, IF)
Elongation (using elongation factors, EF)
Termination (using release factors, RF)
GTP is required for each step of translation.
GTP stands for guanosine triphosphate, a crucial molecule involved in cellular processes, especially in RNA synthesis and energy transfer, similar to ATP, but with a different sugar base (ribose) and nitrogenous base (guanine).
What is translation initiation?
Where do the ribosomal subunits attach in prokaryotes? Eukaryotes?
What are initiation factors?
This is when the small and large ribosomal sub unit bind to the mRNA.
Shine Delgarno sequences, in the 5’ untranslated region of the mRNA, are where the small subunit attaches on prokaryotes.
5’ cap is where the small subunit attaches in eukaryotes.
The charged initiator tRNA binds to the AUG start codon through base pairing with its anticodon within the P site of the ribosome.
Initiation factors assist in the binding together of the small and large subunit. IF are not permanently associated with the ribosome.
When do the small and large subunit of the ribosome attach to the mRNA molecule?
The charged initiator tRNA binds to the AUG start codon through base pairing with its anticodon within the P site of the ribosome.
The large subunit, then binds to the small sub unit, forming the completed initiation complex.
What is the initial AA in prokaryotes? Eukaryotes?
The initial AA in prokaryotes is N-formylmethionine
The initial AA in eukaryotes is methionine (MET, M)
What is elongation?
What sites in the ribosome utilized in elongation?
What does GTP do here?
Elongation is a three step cycle that is repeated for each amino acid added to the protein after the initiator methionine.
A site: holds incoming aminoacyl-tRNA complex. This is the next AA to be added.
P site: (Peptide bond site) where methionine first binds, and where all subsequent AA are joined together with PEPTIDE bonds. Requires peptidyl tranferase, an enzymatic part of the large subunit.
E site: inactivated (uncharged) tRNA chills here and then leaves.
GTP is used for energy in this step.
What do elongation factors do?
Elongation factors assist by locating and recruiting aminoacyl-tRNA and GTP, also helps remove GDP once energy has been used.
What happens with a protein after it has been translated?
What is translation termination?
What are release factors?
When any of the three stop codes move into the A site, a protein called release factor (RF) binds to the termination codon, causing a water molecule to be added to the polypeptide chain.
The water molecule allows termination factors to hydrolyze the completed polypeptide chain from the final tRNA.
The two ribosome subunits dissociate after the polypeptide chain is released from the tRNA and the P site.
There are four kinds of post translation additions of biomolecules processing in the book. What are they?
Phosphorylation: addition of a phosphate group by protein kinases to activate or deactivate proteins. Phosphorylation in eukaryotes is most commonly seen with serine (Ser, S), threonine (Thr, T), and tyrosine (Tyr, Y).
Carboxylation: addition of carboxylic acid groups, usually to serve as calcium binding sites.
Glycosylation: addition of oligosaccharides as proteins pass through the ER and Golgi apparatus to determine cellular destination.
Prenylation: addition of a lipid group to certain membrane bound enzymes.
What is post translational processing?
Nascent polypeptide chains are subject to post translational modification before it will become a functioning protein.
A few things can happen:
Proper folding by chaperones is essential.
Modified by cleavage events, like insulin. (Insulin needs to be cleaved from a larger and active peptide to achieve its active form, makes sense)
Joining of subunits to come together to form quaternary structures (hemoglobin as an example)
Attachment of bio molecules to the peptide, such as phosphorylation, carboxylation, glycosylation, and prenylation.
MCAT concept check translation 7.3 page 270 question 1
What are the three steps of translation?
Initiation
Elongation
Termination
MCAT concept check translation 7.3 page 270 question 2
What are the roles of the A site, P site, and E site in the ribosome?
A site: binds incoming aminoayl tRNA using codon anticodon pairing.
P site: holds growing polypeptide until peptide transferase forms a peptide bond and polypeptide is handed to E site.
E site: transiently holds uncharged tRNA as it exits the ribosome.
MCAT concept check translation 7.3 page 270 question 3
What are the major posttranslational modifications that occur in proteins?
Proper folding of proteins by chaperones
Formation of quaternary structure
Cleavage of proteins or signal sequences
Addition of biomolecules, including phosphorylation, carboxylation, glycosylation, and prenylation.
What is an operon?
E Coli example in the book (trp operon)
An operon is a group or cluster of genes, transcribed as a single mRNA.
Operons are a hallmark of prokaryotic genomes, rare in eukaryotes.
The simplest example of an on off switch that regulates gene expression levels in prokaryotes was discovered in E. coli. The trp operon regulates the expression of many genes according to food sources available to the E. coli in the environment.
Five genes arranged in a cluster on the chromosome in the E. coli encode for enzymes that manufacture tryptophan..
This cluster of gene shares a single common promoter region on the DNA sequence, and these genes are transcribed as a group known as the trp operon (for TRYPTOPHAN operon)
What is the Jacob Monod model for operon?
What are the structural gene?
What is the operator site?
What is a promoter site?
What is a regulator gene?
What is the repressor?
In the Jacob Monod model, operons contain structural genes, an operator site, a promoter site, and regulator gene. Operons are a hallmark of prokaryotic gene organization, much less common in eukaryotes.
The structural gene codes for the protein of interest.
The operator site is upstream of the structural gene and is a non-transcribing region of DNA that is capable of binding a repressor protein.
The promoter site is further upstream from the operator site, it is similar in function to promoters in eukaryotes: it provides a place for RNA polymerase bind.
Furthest upstream is the regulator gene which codes for a protein known as the repressor.
Operons include both inducible and repressible systems. What does that mean?
Inducible and repressible systems offer a simple on off switch for gene control in prokaryotes.
What are inducible systems?
Can they be both positive or negative control?
In inducible systems, the repressor act as a roadblock as it is bonded tightly to the operator system.
The repressor blocks RNA polymerase from the promoter to the structural gene. (The repressor is in the way)
Inducible systems may be either positive or negative control mechanisms.
Systems in which the binding of a protein reduces transcription is negative control system. Systems in which the binding of a molecule increases transcription is positive control mechanism.
Are inducible systems analogous to competitive inhibition of enzyme activity?
Why is this useful?
Inducible systems are analogous to competitive inhibition of an enzyme because as the concentration of the inducer increases, it will pull more copies of the repressor off of the operator region, freeing up those genes for transcription.
This is a useful system because it allows gene products to be produced only when they are needed.
What is the lac operon?
What kind of operon is it (inducible or repressible)? Positive or negative control mechanism?
What is the catabolite activator protein (CAP)?
The lac operon it’s a classic example of an inducible system with a positive control mechanism.
The lac operon contains the gene for lactase.
Bacteria can digest lactose, but it is more energetically expensive than digesting glucose. Therefore, bacteria only want to use this option if lactose concentration is high and glucose concentration is low.
The lac operon is induced by the presence of lactose, thus these genes are only transcribed when it is useful to the cell.
Again, the lac operon is an inducible system with a positive control mechanism.
The lac operon is assisted by binding of the catabolite activator protein (CAP). Falling levels of glucose cause an increase in the signaling molecule cyclic AMP (cAMP), which binds to catabolite activator protein (CAP). This induces a confirmational change in CAP that allows it to bind the promoter region of the operon, further increasing transcription of the lactase gene.
What is positive control mechanism of an operon? Negative control?
Repressive systems?
Can any combination of control and system be possible? What is the lac operon? What about the trp operon?
Negative control: the binding of a protein to DNA stops transcription.
Positive control: the binding of a protein to DNA increases transcription.
Inducible system: the system is normally off, but can be made to turn on given a particular signal.
Repressible system: the system is normally on, but can be made to turn off given a particular signal.
Any combination of control and system are possible:
The lac operon is a induced negative control mechanism because, in the absence of lactose, a repressor protein binds to the operator region, preventing RNA polymerase from binding to the promoter and initiating transcription of the operon’s genes.
The trp operon is a negative control repressor system because, in the presence of sufficient tryptophan, the trp repressor protein binds to the operator, preventing RNA polymerase from transcribing the genes involved in tryptophan synthesis.
What is a repressible system? How do they contrast inducible systems?
What is a corepressor?
What kind of feedback is this?
Repressible systems allow constant production of a protein product.
In contrast to inducible systems, the repressor made by the regulator gene is inactive until it binds to a corepressor.
This is a negative feedback.
How does the trp operon work? Is it inducible or repressive, positive or negative mechanism?
The trp operon operates like this:
When tryptophan is high in the local environment, it acts as a co-repressor.
The binding of the two molecules of tryptophan to the repressor causes the repressor to bind to the operator site.
The cell turns off its machinery to synthesize its own tryptophan, which is an energetically expensive process because of its easy availability in the environmental.
The trp operon (tryptophan trp w) operon is a repressive system with a negative control mechanism.
MCAT concept check control of gene expression in prokaryotes 7.4 page 274 question 1
MCAT concept check control of gene expression in prokaryotes 7.4 page 274 question 2
MCAT concept check control of gene expression in prokaryotes 7.4 page 274 question 3
What are transcription factors?
What is the DNA binding domain?
What is a response element?
What is an activation domain?
Transcription factors are transcription activating proteins that search the DNA looking for specific DNA binding sites.
Transcription factors tend to have two recognizable domains:
DNA binding domain: binds to a specific nucleotide sequence in the promoter region or to a DNA response element (a sequence of DNA that binds only two specific transcription factors) to help recruit transcriptional machinery.
Activation domain: allows for the binding of several transcription factors and other important regulatory proteins (such as RNA polymerase, and histone acetylases) which function in the remodeling of the chromatin structure.
What are cis regulators?
What are trans regulators?
Cis regulators: promoters, enhancers, and response elements (DNA regulatory base sequences) are known as cis regulators because they are in the same vicinity as the gene they control.
Trans regulators: transcription factors, as they need to be produced in translocated back to the nucleus; trans regulators because they travel through the cell to their point of action.
What is gene amplification?
Gene amplification is accomplished by eugenic cells through enhancers and gene duplication.
Sometimes expression must be increased beyond basal transcription (moderate but adequate levels of protein and encoded by a gene in the cell)
What are enhancers?
What are some examples of enhancers?
Enhancers are a form of gene amplification.
Response to elements outside the normal promoter regions can be recognized by specific transcription factors to enhance transcription levels.
Several response elements may be grouped together to form an enhancer, which allows for the control of one gene expression by multiple signals.
Examples of signal molecule and receptor are:
cAMP (cyclic AMP response element binding protein CREB)
Cortisol (glucocorticoid (cortisol) receptor
Estrogen (estrogen receptor)
By utilizing enhancer regions, genes have an increased likelihood to be amplified because of the variety of signals that can increase transcription levels.
How are enhancers effective at gene amplification?
By utilizing enhancer regions, genes have an increased likelihood to be amplified because of the variety of signals that can increase transcription levels.
What is gene duplication?
Cells can increase the expression of a gene product by duplicating the relevant gene.
Genes can be duplicated in series on the same chromosome yielding many copies in a row of the same genetic information.
Genes can also be duplicated in parallel by opening the gene with helicases and permitting DNA replication only of that gene. Cells can continue replicating the gene into hundreds of copies of the gene exist in parallel on the same chromosome.
How does regulation of chromatin structure regulate gene expression?
Recall that heterochromatin is tightly coiled DNA that appears dark under the microscope, is tightly coiled and inaccessible to transcription machinery.
Recall that chromatin is loose and appears light under the microscope in transcription machine machinery can access the genes of interest.
Remodeling of the chromatin structures regulates gene expression levels in the cell.
Histone acetylation is an example.
What is histone acetylation?
What enzymes are responsible?
Histone acetylation is a form of regulation of chromatin structure, where acetylation histone proteins allow for easy access to transcriptional machine machinery to DNA.
Histone acetylase: acetylates lysine residues found in histone proteins, decreasing the positive charge on histone, weakening the histone interaction with DNA, effectively allowing for easier access of the transcriptional machinery to DNA.
Histone deacetylase: removes acetylation of histones. Effectively silencing genetic expression in those regions.
What is an acetyl group?
What is DNA methylation?
What enzyme is involved?
DNA methylation is a mechanism of control over gene expression in eukaryotes.
DNA methylation is involved in chromatic remodeling and regulation of gene expression levels in the cell.
DNA methylase adds methyl groups to cytosine and adenine nucleotides; methylation of genes often linked with the silencing of gene expression.
MCAT concept check control of gene expression in eukaryotes 7.5 page 278 question 1
In an enhancer, what are the differences between signal molecules, transcription factors, and response elements?
Signal molecules include steroid hormones and second messengers which bind to their receptors in the nucleus.
These receptors are transcription factors that use their DNA binding domain to attach to a particular sequence in DNA called a response element.
Once bonded to the response element, these transcription factors can then promote increased expression of the relevant gene.
MCAT concept check control of gene expression in eukaryotes 7.5 page 278 question 2
By what histone and DNA modifications can genes be silenced in eukaryotic cells?
Would these processes increase the proportion of heterochromatin or euchromatin?
Histone deacetylation and DNA methylation will both down regulate the transcription of a gene. (DNA acetylation and demethylation up regulate transcription)
These processes allow the relevant DNA to be lumped more tightly, increasing the proportion of heterochromatin.
MCAT mastery RNA and the Genetic Code page 246 question 1
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