Cell Bio Final TopHat/Homework Questions

Many transcriptional activators are composed of two or more independent _____, each with its own separate function

Domains

Why can't a digest of human genomic DNA be resolved by gel electrophoresis

A typical digest of the human genome produces too many fragments to resolve

The pH of endosmoses and lysosomes is

Acidic

Protein transport into the ER or mitochondria requires unfolding of the protein and threading the amino acid chain through a channel or pore into the organelle. In contrast, protein transport into the nucleus does not require unfolding of the protein. Why is unfolding necessary for nuclear protein import?

Because the protein is carried by an import in protein through the nuclear pore complex

If a human gene is found to have 5 introns, then the mature mRNA encoded by that gene would have how many exons?

Between 1 and 6

WHich of the following lipids are distinctly enriched in lipid rafts?

Cholesterol and sphingolipids

The characterization of restriction endonucleases was a key step in the development of recombinant DNA technology. What is the function of these enzymes?

Cleavage of double-stranded DNA at specific sequences

What are two likely reasons that the NLS is not cleaved off for nuclear proteins?

It is necessary for transporter proteins to bind

Which statement about heterochromatin is FALSE?

It is transcriptionally active

What statement is true about Myosin I

It links actin bundles to the plasma membrane in the microvilli of intestinal cells

What is NOT true of the assembly of actin filaments

It requires ATP

What are the expected phenotypic consequences of a mutation in RanGAP that reduces its affinity for cytoplasmic filaments of the nuclear pore?

It would include less transportation of molecules into the nucleus due to the lack of conversion of GTP to GDP on import in proteins

NADH produced in glycolysis yields fewer ATP molecules than that produced in the citric acid cycle because

Its electrons are shuttled across the mitochondrial inner membrane to complex II

The fibrous proteins underlying the inner mitochondrial membrane are

Lamins

Membrane proteins are able to move

Laterally within the plane of the membrane

Eukaryotic transcriptional activators have activation domains that interact with

Mediator proteins and transcription factors

Injection of MPF into frog oocytes induces them to enter

Meiosis

Transport of glucose into the intestinal epithelium is driven by ion gradients established by the

Na+-K+ pump

Which molecule has a critical role in transcription elongation

P-TEFb

The DNA sequence to which an RNA polymerase binds to initiate transcription of a gene is called a(n)

Promoter

An important step in the import of the transcription factor NF-KB into the nucleus is regulated by a

Protease

SH2 domains are

Protein domains that bind phosphotyrosine-containing peptides

Zellweger syndrome is caused by a defect in

Protein import into peroxisomes

Most of the effects of cAMP in the cell are mediated by

Protein kinase A

What is NOT one of the functions of the cytoskeleton?

Protein translocation into the ER

Tim and Tom are

Protein translocators in mitochondrial membranes

Which of the following is NOT involved in receptor mediated endocytosis

Pseudopodia

What is not involved in the tissue-specific expression of the immunoglobulin heavy-chain gene?

RNA polymerase II

What are the two families of small GTP-binding proteins that are involved in the formation of coated vesicles?

Rab and ARF proteins

LDL uptake by cells is one of the functions of

Receptor-mediated endocytosis

Monosaccharides are to ____ as _____ are to RNA.

Starch; Nucleotides

Lipids play important roles in a number of functions. What is not one of those functions?

Storage of genetic material

In dogs, the Fgf4 gene encodes a protein that regulates bone growth, and in its normal chromosomal location, Fgf4 yields dogs with long legs. WHich statement best explains the mechanism leading to a short-legged phenotype in dogs?

The Fgf4 gene is retrotransposed into the middle of a LINE that contains mutated regulatory sequences that give abnormal expression of Fgf4

What is true about ion channels?

They open either by the binding of ligands or by changes in electrical potential across the membrane

What is the function of karyopherins

They transport macromolecules into/out of the nucleus

Which of the following deletions will not change the reading frame of a gene?

Three nucleotides

Proteins are translated into the ER lumen

Through an aqueous channel created by the Sec61 protein

In the polymerase chain reaction, the purpose of the step in which the temperature is between 70 C and 75 C is

To allow DNA polymerase to synthesize DNA

The primary function of rRNAs in the ribosome is

To catalyze peptide bond formation

The function of telomeres is

To ensure chromosome replication and maintenance

Many cancers arise as a result of a breakdown in signaling pathways that control cell proliferation (T/F)

True

A centrosome is

the major microtubule-organizing center in animal cells

The 5' end of mRNA is modified by

Capping with 7-methylguanosine

The unfolded protein response involves

Increased synthesis of chaperones

As they emerge from the ribosome, signal sequences are recognized and bound by a(n)

Signal recognition particle (SRP)

The term "paracrine signaling" refers to

Signaling between cells located close to each other

During replication, _______ stabilizes the unwound DNA template so it can be copied by the DNA polymerase

Single stranded DNA binding proteins

WHich statement best describes the mechanism of action of miRNAs in blocking expression of proteins?

Single-stranded miRNA in association with the RISC complex, binds to the complementary sequence in the 3' UTR of mRNAs, blocking translation and inducing degradation of the mRNA

The basis for muscle contraction is the

Sliding of myosin and actin fibers past each other

A PCR reaction does not require

Sodium dodecyl sulfate

In prokaryotes, sigma factors are necessary for

Specific binding to certain promoters

Which character is NOT necessary in a plasmid vector to facilitate successful cloning

Strong bacterial promoter

A mutation that causes a G-protein to lose its ability to hydrolyse bound GTP would be expected to have constitutively

Active alpha subunits

What is NOT a commonly observed consequence of the binding of a signaling molecule to its cell surface receptor?

Increased synthesis of the receptor

Which statement about transcription of ribosomal RNA is FALSE

TBP binds the TATA sequence in the promoter of the ribosomal gene

Passive transport across the membrane refers to

Transport in the energetically favorable direction

Why is telomerase important in cancer cells

Abnormal increases in telomerase activity can allow tumor cells to replicate telomeres and keep proliferating indefinitely

The mass of the nuclear pore complex is estimated to be

About 30 times that of a ribosome

The citric acid cycle consists of the oxidation of ______ to produce ______

Acetyl CoA; CO2, NADH, and FADH2

Which of the following is not a function of actin-binding proteins?

Incorporation of micro filaments into the extracellular matrix

What statement about cyclin B is FALSE?

It cycles between active and inactive states in the cell cycle

What is not a destination for vesicles leaving the Golgi apparatus?

Mitochondria

WHich of the following RNAs is RNA polymerase II NOT responsible for transcribing

tRNA

On a typical prokaryotic chromosome, one would find how many telomeres?

0

Approximately what percentage of the mitochondrial proteome is encoded by mitochondrial DNA

1.0%

What is the net yield of ATP molecules per molecule of glucose from glycolysis?

2

You have a piece of circular DNA that can be cut by the restriction nucleases Xhol and Smal. If you were to cut the DNA with both Xhol and Smal, how many fragments of DNA would you end up with?

2

A restriction enzyme with a four-base recognition site would cleave DNA with a statistical frequency of once every

256 bp

The percentage of the average human gene that encodes proteins is approximately

3%

Regarding PCR, place the following in correct order: 1. Annealing - Cool to allow primers to form hydrogen bonds with ends of target sequence 2. Extension - DNA polymerase adds nucleotides to the 3' ends of each primer 3. Denaturation - Heat briefly to separate DNA strands

3-1-2

How many replication origins are there in the human genome

30,000

The human genome is distributed among ____ chromosomes

46 chromosomes

If n represents one copy of single-stranded genomic DNA, then which of the following represents the amount of DNA in a typical cell at G2 of the cell cycle?

4n

Suppose that a gene has three exons and two introns in the following order: 5' exon 1 — intron 1 — exon 2 — intron 2 — exon 3 3' Which of the following could not result from alternative splicing in this gene?

5' exon 2 — exon 1 3'

How many molecules would be produced from two molecules of DNA following five rounds of PCR

64

Taken together, what is the total number of unique nucleotides in DNA and RNA?

8

What correctly describes a cDNA molecule?

A DNA copy of an RNA sequence synthesized by the enzyme reverse transcriptase

A pseudogene is

A gene that arose through gene duplication, but by acquiring mutations became nonfunctional

A molecule that is not membrane permeable binds to a membrane protein on the outside of a cell. This changes the conformation of the protein, causing the binding site to face the inside of the cell. The molecule is then released into the cell and the conformation of the binding site changes again so that it is outside the cell. This is what type of transporter?

A membrane carrier

The feature that most clearly discriminates eukaryotes from prokaryotes is the presence of ______ in eukaryotic cells

A nucleus

MRNA molecules are exported from the nucleus to the cytoplasm via

A recruited protein complex

Suppose an E. Coli cell is in an environment that is rich in glucose and poor in lactose. Which statement best explains gene expression of enzymes used in lactose breakdown?

A repression binds to the operator site of the lac operon and inhibits transcription of the genes involved in lactose breakdown

The ribosomes of the rough ER are targeted to the cytoplasmic side of the membrane via

A sequence within the protein being synthesized

Which statement about introns in the yeast Saccharomyces cervisae is true?

A small percentage of S. Cervesae genes contain introns, and these introns are usually located near the beginning of the gene

Some bacterial promoter regions are regulated by ____ that stimulate RNA polymerase binding and by _____ that block RNA polymerase binding

Activators; repressors

Dynesin and kinesin are similar in that they consist of heavy chains with globular heads which bind both ______ and _______

ATP; microtubules

Mutations in the internalization signal of endocytic receptors prevent their interaction with

Adaptor proteins

Which process both stabilizes and increases the efficiency of translation of an mRNA

Addition of a 7-methylguanosine cap

CAMP is synthesized from ATP by the action of

Adenylyl cyclase

Which statement about cis-acting elements is true?

All of the above

Estimates of mutation rates for a variety of genes indicate that the frequency of errors during replication is much lower than would be predicted on the basis of complementary base pairing. Which mechanisms account for the higher degrees of fidelity?

All of the above (conformational changes in DNA polymerase, 3' to 5' exonuclease activity of DNA polymerase, requirement of a primer for DNA synthesis by DNA polymerase)

Point mutations in DNA result from

All of the above (incorporation of incorrect bases during replication, changes as a result of chemical exposure, changes as a result of radiation exposure)

In the developing of an antibiotic, which of the following would be an effective strategy or target drug?

All of the above (inhibition of translational initiation, induction of premature polypeptide chain termination, inhibition of aminoacyl tRNA binding)

The human genome contains only 20,000 to 25,000 actual gene sequences, yet the human genome can produce up to 100,000 gene products. Which of the following processes accounts for this difference?

Alternative splicing

A feature common to most transmembrane proteins is

An a-helical region of approximately 20-25 hydrophobic amino acids

Which statement about exons is FALSE?

An exon may contain sequences for snoRNAs

Human disease caused by mutations in mitochondrial genomes

Are inherited from the mother

If a drug blocked the activity of mitochondrial inner membrane proteins Tim9 and Tim10, what would most likely not be found in the outer mitochondrial membrane?

B-barrel proteins

All of the following are general transcription factors used in eukaryotic transcription except

BRE

Which of the following RNAs is least stable and has the shortest half life?

Bacterial mRNAs

How does nucleotide-excision repair differ from base-excision repair?

Base-excision repair recognizes and removes single damaged bases, whereas nucleotide-excision repair is more general, recognizing many different lesions that distort the DNA molecule

Typically, nuclear localization signals are composed primarily of

Basic amino acids

MRNAs are degraded in the cytoplasm by

Both a and b (shortening of the poly-A tail and degradation from the 3' end; removal of the 5' cap and degradation from the 5' end)

Which of the following statements concerning elongation of DNA at the replication fork is false?

Both strands are synthesized continuously at the replication fork

The nuclear lamina associates with

Both the inner nuclear envelope membrane and chromatin

What is the function of cofilin in creating a dynamic cytoskeleton?

By cleaving actin filaments, which can lead to further polymerization or degradation of the filaments, which leads to a dynamic cytoskeleton

The signaling molecule nitric oxide (NO) functions

By diffusing across the cell membrane and changing the activities of intracellular enzymes

Which is not a type of histone modification used for controlling gene expression

C-terminal amidation

The major cation responsible for regulating actin-myosin contraction is

Calcium

The amino terminal presequence on proteins imported into the mitochondrial inner membrane is

Cleaved by mitochondrial matrix processing peptidase (MPP)

mutation in the MutS gene is most commonly associated with

Colorectal cancer

Which statement about the relative concentration of Na+ and K+ inside and outside the membrane of a typical mammalian cell is true?

Concentration of Na+ outside the cell is about 30 times higher than inside the cell, and the concentration of K+ inside the cell is 10-30 times higher than outside the cell

Which is a mechanism of histone change that is mediated by chromatin remodeling factors?

Conformational change of histone tertiary structure

Mitochondria differ from other organelles in that they

Contain their own genome

Which steroid hormones are NOT secreted by the gonads?

Corticosteroids

According to the central dogma of molecular biology, transcription of genetic information occurs via

DNA-dependent RNA synthesis

Which step is considered the final aspect of processing an RNA molecule?

Degradation in the cytoplasm

The response initiated by protein kinase A is terminated by

Dephosphorylation of phosphoproteins by protein phosphatase 1

The role of the sigma factor in prokaryote transcription is to

Direct RNA polymerase to bind to different promoter regions

The outer mitochondrial membrane contains proteins that

Direct translocation

Cofilin plays a role in the

Disassembly of actin filaments

Which statement about ABC transporters is FALSE?

Each member of the family is a Cl- channel

The outer nuclear membrane is contiguous with

Endoplasmic reticulum

Cells regulate gene expression to conserve which resource?

Energy

Cell cycle checkpoints ensure that complete genomes are transmitted to daughter cells. DNA damage checkpoints are found in all of the phases, except

M phase

The lumen of the ER is equivalent topologically to the

Extracellular space

After development, liver cells stop cycling and stay in G1 (T/F)

False

All molecules that are in the nucleus are transported by a process that requires GTP (True/False)

False

Avery, Macleod, and McCarty showed that one type of bacteria could be transformed into another type by the uptake of purified RNA. True/False

False

Polypeptides in the ER are usually larger than polypeptides synthesized from the same mRNA that have not entered the ER (T/F)

False

Ribosomal proteins are synthesized in the nucléoles and then assembled onto rRNAs (T/F)

False

The generation of ATP by the mitochondrial ATP synthase is an active transport process. True/False

False

Which statement about the glucose transporter is false?

Flow through it is unidirectional

Ran GAP association with cytoplasmic filaments of the nuclear pore results in the conversion of the nucleotide that is bound to nuclear Ran into

GDP

What is true regarding heterotrimeric G proteins in a resting state

GDP is bound to the a-subunit in a complex with both the B and y subunits

The junctions between animal cells that allow for free passage of molecules smaller than approximately 1000 daltons are called

Gap junctions

In polysaccharides, sugars are linked together by means of what kind of bonds?

Glycosidic bonds

Ribosomes contain one copy of each of 5.8S, 18S, 28S rRNA. The major mechanism ensuring that each is produced in equal molar amounts is the

Grouping of DNA in segments encoding each rRNA into a single rRNA gene

In nucleotide-excision repair of thymine dimers, what is the correct order of enzymatic activity, following damage recognition

Helices —> nuclease —> polymerase —> ligase

In the chromatin around centromeres, nucleosomes are present that have a unique structure in which the core protein ______ is replaced by _______, and this variant of the nucleosome is required for protein assembly at the kinetochore

Histon H3; CENP-A

Which of the following are not phosphorylation by the CdK1/cyclin B complex during mitosis?

Histone H3

The two strands of DNA in the double helix are held together by

Hydrogen bonds between the bases of each strand

In E. Coli, the major enzyme responsible for DNA replication is DNA polymerase

III

A reporter gene is used to

Identify regulatory sequences from the upstream regions of other genes

Transgenic mice carry a foreign gene

In all of their cells

Chromosomes are distributed in the nucleus

In distinct territories

A ribozymes is defined as an enzyme

In which an RNA molecule is responsible for the catalytic activity

The lac operon in E. Coli is regulated by lactose, which

Inactivates a repression of transcription

In proteins being made on rough ER, short spans of hydrophobic amino acids that form alpha helices

Induce a conformational change in the translocations, allowing them to exit the ER membrane

The nuclear basket protein complex is a component of the nuclear pore complex found

Inside the nucleus

What is an example of endocrine signaling?

Insulin release by B cells in the pancreas, mediating the effect of glucose uptake by muscle cells

What is not one of the four major classes of organic molecules in the cell?

Ions

One way that a promoter differs from an enhancer is that it

Is not located far away from the gene it regulates

In cell fractionation experiments in which sub cellular organelles are separated on the basis of their density, the smooth ER is _____ the rough ER

Lighter than

Which of the following are NOT compartments in the nucleus?

Lipid droplets?

WHich of the following transposable elements accounts for ~21% of the human genome?

Long interspersed elements (LINEs)

Which rationale best describes the ability of an enhancer to mediate transcription from very distant sites

Looping of the DNA can occur, allowing the transcription factor to come into the proximity of RNA polymerase

The lac operon is regulated by both a positive transcriptional control system and a negative transcriptional control system. Under what conditions will both systems operate to stimulate transcription of the lac operon?

Low glucose and high allolactose

During mismatch repair in E. Coli, the parental strand is recognized by

Methylated adenines

Which of the following will NOT solubilize a typical peripheral membrane protein

Mildly hypertonic saline

WHich statement about LINEs is FALSE?

Mutation induced by LINEs are exclusively harmful

What statement about LINEs is false?

Mutations induced by LINEs are exclusively harmful

Together, glycolysis and the citric acid cycle directly generate 2 molecules of ATP and 2 molecules of GTP. Most of the energy derived from the oxidation of glucose comes from the oxidation of the ______ generated from ________

NADH; the citric acid cycle

What class of amino acids is buried within the folded structure of the protein?

Non-polar

The human mitochondrial genome encodes only 22 tRNAs. This limited array of tRNAs can read 64 possible triplet corons through extreme wobble in base pairing at the third codon position and the use of a(n) ________ genetic code

Nonuniversal mitochondrial

The most prominent nuclear body is the

Nucleolus

Spliced mRNAs have protective mechanisms to prevent rapid degradation, but introns are rapidly degraded in the

Nucleus

Which of the following is not found in a nucleosome core particle

One molecule of H1 protein

What statement about protein kinase A is FALSE?

PKA binds a total of four molecules of cAMP, one on each of the four subunits

The ingestion of large particles by cells is a form of endocytosis known as

Phagocytosis

Which transport mechanism can bring whole cells into a cell

Phagocytosis

CREB is activated by

Phosphorylation by protein kinase A in the nucleus

Proteins with a C-terminal transmembrane sequence are

Posttranslationally brought to the ER by TRC40, where they remain in the ER membrane with their N-terminal domain facing the lumen

Which of the following is NOT a part of the transcription complex

RFC

The initiator codon in prokaryotes is

Recognized via the Shine-Dalgarno sequence

The nucléoles is the site where

Ribosomal RNA is transcribed and ribosomes are partially assembled

In the "pulse-chase" experiment, Palade and colleagues studied the pathway taken by newly secreted proteins in pancreatic avinât cells by labeling them with radioactive amino acids and then determining their progressive location within the cells. Which of the following represents the correct order from which the proteins were identified?

Rough ER —> Golgi aparratus —> secretory vesicles

You perform an experiment by incubating a radiolabeled nucleotide into the medium of a culture of cells. The cells that take up the radio label would be expected to be in what phase of the cell cycle?

S phase

When a striated muscle is stimulated to contract, calcium is released primarily from the

Sarcoplasmic reticulum

A major function of tight junctions is to

Seal the space between adjacent cells

Which of the following is NOT a contiguous membrane domain?

Secretory granules

Protein transport into the nucleus occurs by

Selective transport through nuclear pore complexes

Though Na+ is smaller than K+,, its passage through K+ channels is blocked by the ____ filter

Selectivity

Most mitochondrial genomes consist of

Several circular DNA molecules

DNA polymerase requires a primer and cannot initiate synthesis de novo. WHat serves as a primer for DNA replication?

Short fragments of RNA complementary to the template strand

Which statement about ion channels is true

THey are opened either by the binding of ligands or by changes in electric potential across the membrane

In some proteins, the only transmembrane sequence is located C-terminally in the protein. These proteins are recognized by

TRC40 (GET3)

Which molecule serves as an adaptor between amino acids and mRNA during translation

TRNA

A protein's alpha hélices and beta sheets fold together to create an overall shape at the _____ level of protein folding.

Tertiary

Cholesterol has a chemical structure similar to

Testosterone and estrogen

What statement about G protein signaling is FALSE?

The alpha subunit becomes deactivated when the protein dissociates from the receptor

Binding of SRP to the signal sequence arrests the further translation of the nascent polypeptide chain. How does the arrest of translation promote the subsequent translocation of the polypeptide chain through the Sec61 translocation complex?

The arrest of translation cause the polypeptide to move through the complex as the tRNA releases the new polypeptide chain allowing the complex

Partial digestion of chromatin with micrococcal nuclease was found to yield DNA fragments approximately 200 bp long. What accounts for this phenomenon?

The binding of proteins to DNA in chromatin protects regions of DNA from nuclease digestion

Peroxisomes are NOT involved in

The biosynthesis of catalase

What reaction will NOT result in water being formed as a product?

The cleavage of sucrose into fructose and glucose

Adherins junctions and des osmoses may be distinguished from each other on the basis of

The linkage of cadherins either to actin filaments or intermediate filaments respectively

What are some possible benefits of the evolution of a nucleus in eukaryotes?

The nucleus can filter which substances enter and leave due to the nuclear pores and the nuclear envelope

What is true of a peripheral membrane protein?

The protein can interact with hydrophilic portions of phospholipids

Whether a microtubule shrinks or grows is determined by

The rate of GTP-bound tubulin addition relative to the rate of tubulin GTP hydrolysis

Which statement about transcriptional termination in prokaryotes is FALSE

The ribosome comes to a UAA, UAG, or UGA stop codon, and transcription ceases

Voltage-sensitive K+ channels are 1000 times more permeable to K+ than to Na+ because

The selectivity filter removes the water molecules from K+ ions but not from Na+ ions

A KDEL sequence is necessary for

The transport of resident ER proteins from the Golgi to the ER

What statement about introns is true?

They are part of a gene, but they are absent from the corresponding mRNA

A member of the heat-shock class of proteins, BiP, is necessary for the proper folding of proteins in the ER, in terms of function, what do BiP and the heat shock proteins (HSP) have in common

They both protect the protein or polypeptide from extracellular environmental factors that may cause the protein to degrade

Which statement about pyrimidique dimers is FALSE?

They can be repaired by photoreactivation in human cells

Which statement describes centraméricain sequences in humans

They consist of A/T-rich-a-satellite DNA, spanning 1-5 million base pairs

How are lncRNAs similar to miRNAs?

They correspond to non coding regions of the genome

G protein-coupled receptors are important molecules involved in signal transduction. Which statements about G protein-coupled receptors is true?

They generally contain seven membrane spanning alpha helices

Which statement is true of all known DNA polymerases

They synthesize DNA in the 5' to 3' direction, and they require a preformed primer hydrogen-bonded to the template

Which statement about introns is true?

Though they are part of a gene, they are absent from the corresponding mRNA

What is NOT a protein translon/transolcase found in the mitochondrial inner or outer membrane?

Toc75

The twisting of the parental DNA strands around each other ahead of a replication fork is relieved by enzymes called

Topoisomerases

RNA is copied from DNA through a process called

Transcription

The role of cytochrome c in the electron transport chain is to

Transfer electrons from complex III to complex IV

The process by which proteins are made from RNA templates is called

Translation

What process does NOT take place in the nucleus?

Translation

Christian Anfisen and colleagues showed that proteins contain all the information to spontaneously fold into an active enzyme. Yet sixty years later, we can still not predict the 3-D shape of a protein from its amino acid sequence. True/false?

True

Nucleosides are an impediment to transcription in eukaryotic cells (True/False)

True

The progression from metaphase to anaphase is triggered by

Ubiquitin-mediated proteolysis of key proteins

Deamination of cytosine results in the conversion of cytosine to

Uracil

What is NOT involved in protein transport into mitochondria?

Vesicular transport

The directionality of nuclear protein import is determined by

an unequal distribution of Ran/GTP

Glucose repression is mediated by several positive transcriptional control mechanisms. What is NOT one of those mechanisms?

cAMP-activated CAP transcribes genes that metabolize lactose

Two examples of membrane lipids that are present in small amounts are

glycolipids and phosphatidylinositol.

THe ENCODE project revealed that as much as 75% of the human genome is actually transcribed into RNA. Most of this is non-protein coding RNA. WHich of the following include two new classes of non coding RNA discovered by the ENCODE project?

microRNA and lncRNA

The enzyme that synthesizes DNA using RNA templates is called

reverse transcriptase

What statement regarding tRNAs is FALSE?

tRNAs differ in sequence only at the anticodon