BIOL 3010 QUIZ 1

What are two things that can allow cis regulatory elements and promoters on a gene have access to Transcription Factors?

1. ATP-dependent remodeling by nucleosome sliding, displacement and modification 2. Access by "pioneer transcription factors"

What are the common characteristics for the major families of chromatin remodelers (SWI/SNF, CHD, ISWI)?

1. Have affinity for nucleosome 2. Domains to recognize histone modifications 3. ATPase domains for overcoming DNA interactions 4. Domains for interactions with other proteins.

Hypothetical evolutionary intermediates for RNA (in favor of RNA as the 1st genetic material)

1. Instead of using AUGC bases, hypoxanthine could have been used. 2. Alternate bases for ribose: threose, glutamine, aspartate. 3. Different linker: instead of phosphate use aspartate. 4. Using formamide instead of water. 5. Possible that the original solvent wasn't water- molecules would rehydrate instead when water returned. 6. Cofator- could've been Fe2+ not Mg2+.

Issues with the assembly of RNA as first Genetic Material:

1. It is complex (requires 3 chemical parts) 2. Nucleotides need activation for bonding. 3. Phosphates would be sequestered in minerals and unavailable. 4. Adenine was the only nucleotide possibly abundant. 5. Ribose unlikely to be synthesizable without a biological organism and is unstable. 6. RNA is unstable in water and water is a solvent. 7. Different cation availability. 8. Natural RNA polymerase ribozymes unknown.

3 Premendelian Understandings of Inheritance

1. Preformationism (belief that entire organism was preformed in the sperm). 2. Inheritance of acquired characteristics- the idea of "use or disuse." This was tested by cutting off the tails of mice for 5 generations; but after 5 generations, the tails didn't shorten. 3. Blending inheritance- idea that progeny will have blended phenotypes.

What is the RNA World Hypothesis?

1. RNA molecules are first genetic info and could assemble themselves from a nucleotide soup. 2. RNA evolves and diversifies, which would give material for selection. 3. RNA molecules acquired the ability to make proteins, which requires tRNA to evolve first. 4. Finally, RNA was involved in the transition for DNA to appear. Once DNA appeared, this would provide more fidelity due to double stranded structures.

Law of Segregation

2 alleles (one from each parent) segregate during gamete formation and then unite at random during fertilization.

What are transposable elements?

A DNA sequence that can change its position within a genome, sometimes creating/reversing mutations and altering the cell's genetic identity and genomic size. They can have genes within them and they are found all over the genome. They don't code proteins. Most of the time, they don't have a role- the genome just "tolerates" their existence. Some are autonomous of the genome.

How is the 5' Cap added?

A Methyl G is added onto the ribose sugar, and the sugar is attached to another sugar through a triphosphate bridge. The cap helps efficiency of translation and protects the transcript from degradation.

What are UORFs?

A distractor that dampens translation. ???

How many genes are in the genome?

Around 20,000 genes that code for humans and 20,000 that don't code.

What Experiment showed that genes code for proteins?

Beadle and Tatum demonstrated this. They took a strain of bread mold, grew it in vitro, took the strain and exposed it to X rays (causing mutations), then crossed the strain with another WT, creating spores. They took the spores and put them in cultures with complete medium to see if they'd grow. They took the ones that grew and put them on minimal medium. Then, out of the ones that survived on complete but died on minimal, they figured out that they need some sort of essential factor. They added certain substances fort these specific spores with minimal medium to observe growth. When Arginine was added, they grew. Following this, they added different levels of precursors leading up to Arginine. Because the spores had mutations, it demonstrated the different steps; some would only grow with the precursors closer to Arginine. This allowed them to infer which enzymes in the pathway are affected.

Artificial Selection

Breeding organisms in order to select for certain phenotypes. This was done with organisms such as maize, tomatoes, and dogs.

What does the Zika Virus demonstrate in the cell cycle?

Cells with Zika don't undergo mitosis correctly and information is lost. The chromosomes don't separate properly, causing cell death.

How did Chargaff's work demonstrate complementary base pairing of nucleotides?

Chargaff found that the relative percentages of A and T are the same and C and G are the same across several different species, suggesting that they pair together.

What are Cis Regulatory and Trans Regulatory Elements?

Cis Regulatory elements are specific motifs in DNA that modulate transcription and tend to be very small. They serve as recognition sites for proteins like RNA Pol and can be in introns and UTRs. Trans Regulatory elements, on the other hand, do not exist on the same gene that they regulate.

What is the Central Dogma and why isn't it always true?

Claims that DNA is transcribed into RNA, RNA is translated into protein. However, this is not always a linear sequences (ex: retroviral DNA).

What are the two building models of the original RNA?

Classical model: assemble each nucleotide first and then put them together (bases then adaptors then the linkers) - one nucleotide at a time. Polymer Fusion Model: First do the base pairs and then do the polymerized backbone.

What are cohesins? How do noncoding RNAs and enhancer regions affect the MC?

Cohesions hold different DNA regions together. Upstream DNA segments are transcribed into noncoding RNAs that interact with the mediator and stabilize it. Enhancer regions also stabilize the MC by activating TFs.

What is a Dual Function TF? How does thyroid hormone T3 demonstrate this?

DFTFs can activate/repress gene expression. When T3 is present, it binds to TR, which is bound to RXR. Then, HAT is recruited and transcription is activated. Without T3, a repressor complex forms and the activator complex is released. HDAC is recruited and deacetylation occurs, increasing histone/DNA interactions. Additionally, there is a conformation change in TR and so different sites are exposed that aren't visible normally to activators but instead repressors and CR elements. Transcription decreases.

How do combinations of histone modifications and DNA modifications regulate transcriptional state and its flexibility?

DNA can be modified as well. Histone modifications and C methylation are examples of epigenetic modifications that affect gene expression. Cross generational, sex-specific DNA methylation for a few hundred genes results in "genomic imprinting" that affects gene expression in offspring.

What is DNA methylation in context of transcription and where does it occur?

DNA methylation is a modification that decreases transcription and occurs in regions with many Cs and Gs (CpG islands), often near promoters. If there is some activator associated with CpG island, TFs will initiate transcription on the gene. If not, the region can be recognnized by DNMT (DNA methyltransferase), which adds a methyl group on the C on the opposite strand. This methylation can have repressive functions.

How is methylation of DNA transmissible to daughter cells? How do the globin genes demonstrate this?

DNA methylation occurs during embryonic development. As a cell divides, regions that are methylated will stay methylated. At 6 weeks old, embryos have E globin with a promoter that is unmethylated and therefore active. Meanwhile, gamma globin is methylated and inactive. At 12 weeks, however, E globin's promoter is methylated and therefore E globin is inactive. Gamma globin promoter is unmethylated at this time and then gamma globin becomes transcriptionally active.

When do we know for sure that methylation causes decreases transcription?

DNA methylation only

In what state does DNA normally exist? Describe the histone/DNA structure.

DNA normally exists as heterochromatin with tightly associated variety of proteins. Chromatin consists of DNA and protein. A loop forms two times around the histone from DNA and DNA interacts with 8 histone plus 1 linker.

What are 2 examples of Minor Groove Intercalators and what are their effects?

Dapi DNA Stain intercalates into the minor groove and is can be detected with fluorescence is. This shows where nucleus in the cell is. Furanocoumarins are another type of intercalators that make a variety of secondary metabolites which get into the minor groove and form adducts, preventing DNA from being replicated. For example, Psoralen results in lesions.

What does In Situ demonstrate?

Demonstrates where RNA goes and shows patterns of gene expression (like where RNA is transcribed).

Explain the 2 examples of Ribosomapathies

Diamond Blackfan Anemia: RPS mutation that impairs 18S rRNA production which reduces a small amount of ribosomal subunits. Treacher Collins Syndrome: Mainly TCOF mutation that causes loss of treacle protein = no RNA Pol1 localized to the nucleus.

How does alternative splicing affect the transcript?

Different regions may or may not be included post-splicing, varying the transcript and driving diversity.

Describe the activation of S phase in terms of TFs. What happens if Rb has a mutation?

E2B is normally inhibited by Rb. However, Cyclin (specifically D/E), the regulatory subunit of CDK, can bind to CDK and phosphorylate the Rb, allowing it to dissociate off of E2F. If Rb has a mutation and can't inhibit E2F, E2F is constitutively active and causes excessive proliferation.

What do ChiP Seq results show?

Essentially, the more frequently a gene shows up for a specific protein, the more likely that the protein is associated there. Ex: Peak of RNA Pol 2 signifies the start in transcription. This is where RNA Pol 2 is hanging around waiting to start transcription. This is called transcriptional priming. Ex: H3K27me3's increased presence signifies a decrease in transcription

Once the DNA is accessible (after going through remodeling and binding from PTFs) what will occur? What are the 3 types of RNA Pols?

Essentially, transcription factors will get RNA Pol to come in. RNA Pol1 is in charge of 18S/28S rRNAs. RNA Pol2 is in charge of mRNA and some small RNAs. RNA Pol3 is in charge of tRNA, 5S rRNA, and some other small RNAs.

What are euchromatin and heterochromatin?

Euchromatin is open chromatin that is more accessible to RNA polymerase and transcription factors and is more likely to be transcriptionally active. Heterochromatin is closed chromatin that is tightly packed with nucleosomes, is less accessible, and less likely to be transcriptionally active.

How do cancer cells have different splicing of genes?

Ex: CD44 exon is not spliced out, causing increased cell proliferation. Normally, the exon should be spliced out for contact inhibition to occur and prevent cell proliferation. The lack of splicing exons inhibits apoptosis.

What are cis/trans splicing regulators?

Exonic/Intronic Splicing Suppressors/Enhancers. Suppressors bind to hnRNP which suppresses splicing nearby. Enhancers are targeted by SR.

What are the experimental evidence for RNA replicating enzyme? How did it evolve?

Extant ribozymes that are present today don't necessarily have replicase activity; however, you can select for the ability to go after RNA triplet codons to alleviate secondary structure constraints. In vitro, 6 different types of ribozymes were identified. Type 1 alone had no catalytic activity while the others did; When Type 1 was added to Type 5, it enhanced elongation. This raised the possibility that if the ancestral type worked on triplets, it ended up specifically later on coding for AAs.

How were different AAs generated experimentally?

First, a synthetic mRNA was created with repeating nucleotides (Poly-U first), then other patterns. Then, other patterns were used to generate different types of AAs.

How does methylation occur on residues, specifically Arginine and Lysine?

For methylation, PRMTs can add 1-2 methyl groups on Arginine. HMTs can add 1-3 methyl groups on Lysine.

How do the nucleotide bases bond together? Which are purines and which are pyrimidines?

G and C bond with 3 H bonds. A and T bond with 2 H bonds A and G are purines, while C and T are pyrimidines.

What are G1, S, and G2

G1- from time mitosis finishes until DNA is replicated. Most cells are going to stay here to Grow, make proteins. S- DNA synthesis and chromosomal development. G2- gap before mitosis.

What are the four characteristics of genetic material?

Genetic material: Stores information. Expresses information. Replicates information. Accommodates for variation.

What is the C Value Paradox and one example of it?

Genome size doesn't correlate with organismal complexity. For example, the axolotl has a huge genome but it is not as complex as a human's genome. Its intronic size is 5-20x larger than a human's due to evolution, and there exist much more repeated sequences.

What experiments showed that genetic information can be transferred and how did it show this?

Griffith's Experiment in 1923 demonstrated this. Mice were injected with an S strain bacteria and then they died. Sometimes, the S strain mutated to R strain, and when that is injected, the mouse lives. If you heat kill the S strain, the mouse lives. However, if you heat kill the S strain and combine it with the live R form, the mouse dies. This tells us that the R form received some sort of the information from the cellular components of the S dead form. The next experiment that was done combined the living R form with the heat killed S form, which resulted in the live R form transforming into the S form. Different things were added to test what caused the transformation (Proteases, RNAses, DNAses). The DNAse prevented the transformation to occur, which shows that DNA was the source of this.

How does H2A-B Lys91 Ac and H3Lys56AC (DNA Breathing) affect DNA accessibility? How was this experimentally determined?

H2A-B Lys91Ac promotes the disassembly of the nucleosome. H3Lys56Ac results in DNA Breathing, allowing the DNA to interact less with the histone octamer and come off of it. This was determined experimentally using FRET. The DNA was labeled with 2 fluorescent molecules that are Red and Green. When the 2 molecules are in proximity, and hit with the right wavelength, the you can see the visible output of light. Findings: FRET tells you when DNA is closer/further apart from the histone. The peaks in the graph DNA when the DNA is close to the histone.

What are some examples of some modifications that result in targets for other proteins?

H3K9me recruits HP1 which can silence transcription by recuiting HMTases which perpetuate a heterochromatic state. Another example is Polycomb Complex, which is recruited to H3K27me/ac to enforce transcriptional silencing.

What does a mature mRNA contain?

Has a cap, poly A tail, and intronic sequences spliced out.

What are histone variants and what is an example of one?

Histone variants are other types of histones that have a variety of functions. Experimentally, DNA was damaged using a laser and it was seen that H2AX was recruited in response.

How does DNA methylation lead to histone methylation? How is MeCP involved?

In highly methylated regions, MeCP can recruit HDAC. This leads to tighter packing of chromatin, repressing transcription via deacetylation. MECP can also recruit histone methyltransferase and the histone will be methylated, repressing transcription.

What is elongation and what are the two phases?

In this phase, the DNA template is transcribed 3' to 5' by RNA Pol. There is a transcription bubble that is around 30 nucleotides long, has RNA Pol2 adding nucleotides at the 3' end of the nascent RNA, and this is where the DNA is melted apart. The two phases are: Early Elongation Productive Elongation

What is the Proximal Promoter?

Initiates transcription.

What is CHiP Seq and how is it performed?

It is used to find out where/what a protein is doing on chromatin (DNA and protein). 1. Isolate chromatin from the whole genome. 2. Fragment chromatin into small pieces. 3. Incubate with antibody to protein of interest; precipitate antibody-chromatin complexxes. 4. Purify the DNA from the precipitated material by using a column. 5. Sequence DNA via NextGen Sequencing. 6. Align sequences to genome to detect regions that had been enrich for protein of interest. Now, you can see the specific regions that had that protein.

How does RNA Pol2 pause? What are the 3 mechanisms?

Kinetic: Can have a Negative Elongation Factor come and stop Pol2. Barrier: RNA Pol2 can't cross a barrier. Interaction: a tethering factor prevents RNA Pol2 from continuing.

What are missense and nonsense mutations? How was the collinearity of protein/DNA sequences?

Missense: change which AA is made. Nonsense: change AA to a stop codon. Looked in E coli where the mutations were and where they were altered. It indicated a collinearity of protein/DNA sequence and found missense mutations that turned nonsense.

3 examples of defective problems with RNAs

Nonsense: makes random STOP codon mutation Nonstop: RNA Pol2 keeps going past PolyA (makes RNA too long) Nogo: RNA Pol2 blocked

How are nucleosomes changed in the presence of remodelers? What are the different mechanisms of remodelers?

Nucleosomes are repositioned (slid downstream) to open spots for proteins to enter and changes to be made to the DNA (post translational modifications). Different mechanisms include: repositioning, ejection unwrapping, dimer exchange (making a variant), or dimer ejection.

What are nucleotides and nucleosides?

Nucleotide: sugar + base + PO4- Nucleoside: sugar + base

How does translation occur?

Occurs in 3 stages (initiation, elongation, termination). The Small subunit first goes on the mRNA @ the initiation site. tRNA goes on and the large subunit goes on over it. Second tRNA comes onto the A site and the 1st AA (Met) is transferred to the next tRNA and the ribosome moves along. Elongation continues as the peptide is transferred as the ribosome translated. A stop codon causes the release factor to enter the A site and Termination is reached. Then, the ribosome dissociates and the newly formed protein is released.

How do PTFs function? How does its structure allow this?

PTFs can bind DNA even in the heterochromatic state. They initiate chromatin remodeling and allow for the binding of other TFs, histone variants, and remodelers (to open up the chromatin). For example, PTFs can recruit HAT and other proteins. Additionally, they are able to stabilize euchromatin. The structure of PTF is similar to the structure of the linker histone, making it easier to make changes.

What are 4 ways activators are regulated?

Phosphorylation: when the TF must be phosphorylated before it binds. Co-Factor Interaction: when the TF must bind to an additional factor and once it's bound, then it can interact with the DNA. Ligand Binding: 2 factors need to bind together and once the ligand is bound, then it can activate. Cleavage from inactive precursor: The activator is floating in the cytoplasm and part of it needs to be cleaved to do the initiation.

Why could RNA be the first genetic information?

RNA encodes information, has complex folding (superior to DNA's less flexible double helix structure), is highly conserved across life forms, and has enzymatic properties.

What is the RTK pathway?

RTKs phosphorylate tyrosine residues and recognize ligands in extracellular space. They can affect transcription in the nucleus and can interact with the MC.

What needs to be done to make the final mRNA?

Remove introns, add 5' Cap, Add poly A tail, complete termination

How do Transcriptional repressors/co-repressors block expression? What are the 4 mechanisms of repressors to prevent transcription?

Repressors/Corepressors can interfere with the Pol2 Complex either physically or by promoting closed chromatin via histone modifications. Competition: the repressors takes the spot of the activator Quenching: when the repressor binds to the activator and stops it Cytoplasmic sequestration: when the repressor binds to the activator in the cytoplasm and traps it from going to the nucleus. Heterodimerizing: can sometimes repress transcription.

What are some of the enzymatic properties of RNA?

Ribonuclease P for example cleaves phopshodiester bonds on tRNA and other small RNA. In vitro, you can separate the protein and RNA components - RNA by itself can act as an enzyme. Upon using Ribonuclease P in vitro, it is a ribozyme, and evidence that RNA has enzymatic abilities. Additionally, self splicing introns (which remember are mRNA) exist. These splice themselves out without other proteins, suggesting that RNAs can generate variation due to this potential for changes.

Deoxyribose versus ribose

Ribose has an -OH group on the 2' C, whereas deoxyribose has a -H.

Describe mRNA degradation.

Rionculeases candegrade RNA. Poly A nuclease removes the tail. Ribozymes can recognize premature termination codons and can target RNA for degradation. TRAMP identifies defective RNAs and targets them for degradation.

How does malaria immunity demonstrate the effects of mutations?

Some people are naturally immune to malaria because they have a subtle mutation in 1 nucleotide. The PTF GATA is unable to recognize the site and the chemokine receptor called the Duffy Antigen isn't expressed as much anymore because the TF doesn't know to express it. Now, when the parasite comes in, it cannot get within the blood cells because it can't find the Duffy Antigen.

What are the 3 motifs needed for splicing?

Splice donor (5' that always has a GT), Branch (with a critical A), and the Splice Acceptor (3' that always has the AG).

What is TF structure like? What are the domains of TFs?

TFs are modular structures with separable domains for DNA binding, dimerization, activation, ligand binding, etc. Has 3 domains: Activating: works with the MC DNA binding domain: binds DNA Connecting domains: connects the previous two domains.

What is the experimental evidence for the Semiconservative Replication of DNA?

Take E coli and grow it in the 14 N first, extract the DNA from the cells and centrifuge it Then, grow E coli in the 15N, and DNA turns out to be heavier and sediments lower. Then, took this DNA from the 15N medium and grew it in the 14 N and found a semiconservative DNA result.

What did Mendel demonstrate from his work with the sweet peas?

That both parents contribute to the next generation and each plant carries 2 copies of a unit of inheritance (called a gene) and these copies can differ (alleles). His work also demonstrated the concepts of dominance and recessivity.

How is the MC involved in transcription? What are some of its key roles?

The MC is comprised of 30 proteins and promotes the assembly of PIC and Pol2 localization. It integrates and communicates with the TFs bound to cis regulatory elements and some noncoding RNAs that regulate transcription. It makes a bridge of TFs to come. Has communication with far away CREs to help transcription. The MC promotes looping of DNA resulting in spatially clustered activating Tfs near the TSS. It regulates Pol2 pausing after it has transcribed 30-60 nucleotides as well.

How are cis-regulatory elements/motifs and TFs involved in initiation and the formation of the PIC? What is the PIC and how does she form?

The motifs such as TATA, BRE, Inr, and DPE cooperate to promote transcription. The TATA Box gets transcription going and has a TBP (a TF) which is part of the PIC and binds there. The Inr/Initiator is in the region where transcription starts, which overlaps with the TSS. Additionally, the PIC has to be assembled on the spot, and is comprised of 50 proteins. It is a cluster of TFs that are recruited by the promoter motifs. PIC has an important role in interacting with the mediator complex.

What is the spliceosome? What does it do?

The spliceosome has RNAs and proteins and snRNPs. It cuts at the 5' GU area and then the free end folds over to make a lariat, attached to A on the 2' covalently (creating a lariat loo). This triggers the release on the other end, separating from the splice acceptor.

When does natural selection occur?

There are 3 main components necessary: variation must occur amongst individuals in a population for a certain trait; fitness differences - meaning a consistent relationship between the value of a trait and reproductive success; and inheritance, a consistent relationship for value of trait between parents and offspring.

Genome Density

There exists variation across the genome for how densely packed genes are. Areas called gene deserts are not very condensed.

What are SSRs (Simple Sequence Repeats)?

These are repeated sequences that comprise 50% of the genome and are prone to being expanded/contracted due to errors. There is ~1SSR per 2Kb.

What are Histone Tail Modifications? What are two types?

These are specific AAs subject to post-translational modification. These modification help regulate open/closed chromatin. For example: acetylation, methylation.

How do cancerous cells behave in regards to gene expression?

They exhibit grossly dysregulated gene expression, creating the opportunity for new variants to be selected, because cancer genomes are extremely unstable and DNA repair functions are typically malfunctioning. One common mutation is Lys27M, which is resistant to methylation and acetylation.

What is a bHLH?

This is a DNA binding domain that stabilizes DNA and activates transcription. It extends into the minor grooves of DNA to recognize certain bases. It uses a 2 Leucine Zipper Domain to insert itself and interact with Hydrogen bonding.

What is Polyadenylation and how does it occur?

This is the addition of the PolyA tail at the 3' end. This protects the transcript from degradation. There are factors that recognize the motif in RNA and poly A onto it. Before this, the nascent RNA must be clipped by a ribonuclease that recognizes a GU rich motif and does the cleavage. Then, the 3' end can be polyadenylated.

What is Early Elongation? Why does RNA Pol 2 pause?

This lasts for 20-60 nucleotides. Then RNA Pol2 pauses in order to regulate accuracy and then quickly go and express the rest.

What is done if there is DNA damage? What happens in the G1/S checkpoint?

This makes replication hazardous (as that would spread the damage). The P53 protein responds to DNA damage by inducing expression of CDK inhibitors, such as P21, which can prevent Rb from being phosphorylated by inhibiting it.

What is productive elongation? How is RNA Pol2 unpaused?

This occurs rapidly through termination. RNA Pol2 is eventually released by the elongation factors. Recruitment factors such as PTEFb complex, ELL, and FACT (which facilitates nucleosome transfer and drives nucleosome disassembly) can unpause it.

What is termination?

This promotes the output by reducing Pol2 time on the template and time to reinitiation. It reduces the interference with neighboring genes, limits targeting of RNA for degradation, increases post-transcriptional processing efficiency.

What does production of translatable mRNA from specific genes require?

This requires: 1. Accessibility of genes to TFs. 2. Interactions of TFs with cis-regulatory elements. 3. Initiation, elongation, and termination of RNA transcript. 4. Processing of newly transcribed RNA. 5. Transport of Processed mRNA to cytoplasm.

How is DNA strung together/polymerized?

Through phosphodiester bonds.

How are transcription rates affected? How does this affect exons?

Transcription rates are affected by acetylation/methylation as well. For example, H3K9Ac causes increased transcription, causing RNA Pol2 to transcribe faster and create larger loops, meaning it is easier to splice an exon. H3K9Me causes a decrease in transcription, and slows down the speed of it.

How does a typical gene body look like? What are some different parts?

Transcription starts where the exon begins at the TSS. Genes can have >1 TSS. The gene body includes both the exons and introns combined.

What is an UTR?

Untranslated region. This is packaged into the final mRNA and doesn't code. They exist within exons.

How do frameshift mutations indicate the existence of codons?

When 3 nucleotides were inserted/deleted, you still get a functional protein, suggesting that the number 3 is important and suggests existence of the codon. Adding/deleting less than three nucleotides, however, would result in a nonfunctional protein.

How does Lysine acetylation occur and how does this affect transcription? What proteins are involved in this modification?

When HAT puts acetyl on the histone, this removes the positive charge from the histone, so the histone doesn't have as tight as an interaction with the negatively charged DNA. When you add the acetyl group, this increases the mass and transcription due to the lessened interactions with DNA- now it's easier to take apart. When HDAC removes the acetyl group, then the positive charge returns.

What happens if you miss/skip over an acceptor and go to the next one?

You'll lose an exon because the donor sites are functionally equivalent.

What are some of the different forms that DNA can take on?

Z DNA, which spirals left, B DNA, which spirals right. Can also take on form of linear or circular DNA.

How is tRNA involved in translation?

tRNA serves as the adaptor between codons and AAs. They recognized the codon and bring AA. The Aminoacyl tRNA synthetase covalently attach AAs to form amino acyl tRNAs, using ATP. Most tRNAs recognize more than one codon.