biology chapter 17: gene expression from gene to protein

mutation facts

-A deletion mutation results in the loss of a base in the DNA sequence. - An addition mutation results in an added base in the DNA sequence. - Addition and deletion mutations disrupt the primary structure of proteins. - A knock-out mutation refers to the loss of a protein's function but not necessarily to its complete absence.

What is the proper order of the following events in the expression of a eukaryotic gene? 1. translation 2. RNA processing 3. transcription 4. modification of protein

3,2,1,4

The direction of synthesis of an RNA transcript is _____.

5'-3' Nucleotides are added to the 3' end of RNA.

Which of the following steps occurs last in the initiation phase of translation?

The large ribosomal subunit joins the complex. This step occurs after the 5' mRNA is bound by the ribosome and the start codon is bound by an aminoacyl tRNA.

Which of the following is a post-translational modification of a polypeptide?

Cleavage of a polypeptide into two or more chains is an example of a post-translational modification of a polypeptide. Additional steps—post-translational modifications—may be required before the protein can begin doing its particular job in the cell. Certain amino acids may be chemically modified by the attachment of sugars, lipids, phosphate groups, or other additions. Enzymes may remove one or more amino acids from the leading (amino) end of the polypeptide chain. In some cases, a polypeptide chain may be enzymatically cleaved into two or more pieces. For example, the protein insulin is first synthesized as a single polypeptide chain but becomes active only after an enzyme cuts out a central part of the chain, leaving a protein made up of two polypeptide chains connected by disulfide bridges. In other cases, two or more polypeptides that are synthesized separately may come together, becoming the subunits of a protein that has quaternary structure. A familiar example is hemoglobin.

Polypeptides are assembled from _____.

amino acids

What enzyme catalyzes the attachment of an amino acid to tRNA?

aminoacyl-tRNA synthetase

RNA polymerase

an enzyme that pries the two strands of DNA apart and joins together RNA nucleotide complementary to the DNA template strand - thus elongating RNA polynucleotide -like DNA replication , RNA polymerase can assemble only in its 5'-3' direction -BUT RNA can start a chain from scratch whereas DNA needs a primer to start

The structures called snRNPs are __________.

are part of a splice some The structures called snRNPs are part of a spliceosome. Particles called small nuclear ribonucleoproteins, abbreviated snRNPs (pronounced "snurps"), recognize these splice sites. As the full name implies, snRNPs are located in the cell nucleus and are composed of RNA and protein molecules. The RNA in a snRNP particle is called a small nuclear RNA (snRNA); each snRNA molecule is about 150 nucleotides long. Several different snRNPs join with additional proteins to form an even larger assembly called a spliceosome, which is almost as big as a ribosome. The spliceosome interacts with certain sites along an intron, releasing the intron, which is rapidly degraded, and joining together the two exons that flanked the intron.

mutations

are responsible for the huge diversity of genes found among organisms because mutations are the ultimate source of new genes

domains

areas on proteins, in which they often have a modular architecture consisting of discrete structural and functional regions -for example one domain of an enzyme may be set for an active site while another domain of a protein may allow it to bind to a cellular membrane - -overall exons code for the different domains of a protein

What is the main difference between DNA replication and RNA translation?

DNA réplication is to replicate genes while RNA translation is to use the DNA to express proteins and what to do with them throughout the body

True or false. A tRNA with an anticodon complementary to the stop codon catalyzes the reaction by which translation is terminated.

False it is not actually an anticodon that couples with the stop codon rather the release factors that do There are no tRNAs complementary to the three stop codons; termination occurs when release factors recognize the stop codon in the A-site and catalyze the release of the polypeptide from the tRNA in the P-site.

Which of the following catalyzes the linkage between ribonucleotides to form RNA during gene expression?

RNA polymerase catalyzes the linkage between ribonucleotides to form RNA during gene expression. ribonucleotides, AUGC to form RNA Transcription is the synthesis of RNA using information in the DNA. The two nucleic acids are written in different forms of the same language, and the information is simply transcribed, or "rewritten," from DNA to RNA. Just as a DNA strand provides a template for making a new complementary strand during DNA replication, it also can serve as a template for assembling a complementary sequence of RNA nucleotides. For a protein-coding gene, the resulting RNA molecule is a faithful transcript of the gene's protein-building instructions. An enzyme called an RNA polymerase pries the two strands of DNA apart and joins together RNA nucleotides complementary to the DNA template strand, thus elongating the RNA polynucleotide.

What name is given to the process in which pre-mRNA is edited into mRNA?

RNA processing RNA processing edits the RNA transcript that has been assembled along a DNA template. this is the second step after transcription

RNA molecules that function as enzymes are called __________.

Ribozymes The idea of a catalytic role for the RNAs in the spliceosome arose from the discovery of ribozymes, RNA molecules that function as enzymes. In some organisms, RNA splicing can occur without proteins or even additional RNA molecules: The intron RNA functions as a ribozyme and catalyzes its own excision! For example, in the ciliate protist Tetrahymena, self-splicing occurs in the production of ribosomal RNA (rRNA), a component of the organism's ribosomes. The pre-rRNA actually removes its own introns. The discovery of ribozymes rendered obsolete the idea that all biological catalysts are proteins.

Stop codons are unique because they __________.

Stop codons are unique because they do not code for amino acids rather allows a releasing factor to bind to the A site of the ribosome. The final stage of translation is termination. Elongation continues until a stop codon in the mRNA reaches the A site of the ribosome. The nucleotide base triplets UAG, UAA, and UGA do not code for amino acids but instead act as signals to stop translation. A release factor, a protein shaped like an aminoacyl tRNA, binds directly to the stop codon in the A site. The release factor causes the addition of a water molecule, instead of an amino acid, to the polypeptide chain. (There are plenty of water molecules available in the aqueous cellular environment.) This reaction breaks (hydrolyzes) the bond between the completed polypeptide and the tRNA in the P site, releasing the polypeptide through the exit tunnel of the ribosome's large subunit. The remainder of the translation assembly then comes apart in a multistep process, aided by other protein factors. Breakdown of the translation assembly requires the hydrolysis of two more GTP molecules.

DNA does not store the information to synthesize which of the following? DNA Organelles Messenger RNA Proteins

Synthesis of organelles is not directly coded in the DNA

RNA processing converts the RNA transcript into _____.

The editing of the RNA transcript produces mRNA. this is part of the second step in the transcription/translation process The mRNA will make it over to the cytoplasm where it will be inserted into the ribosome as the template of which tRNA will provide the anticodons of the amino acids

What happens to RNA polymerase II after it has completed transcription of a gene?

The enzyme is free to transcribe other genes in the cell.

The initiator tRNA attaches at the ribosome's _____ site.

The initiator tRNA attaches to the ribosome's P site.

types of RNA

bacteria have a single type of RNA that performs many functions including synthesizes but also functions of proteins. -in eukaryotes, have at least three types of RNA polymerase , in the nucleus - 1. the one used for pre mRNA synthesis , called RNA polymerase II 2. the other two transcribe RNA molecules that are not translated into proteins

After an RNA molecule is transcribed from a eukaryotic gene, what are removed and what are spliced together to produce an mRNA molecule with a continuous coding sequence?

introns; extons Introns, intervening sequences, are removed and the exons, expressed sequences, are spliced together. Exons are expressed regions

Because the bacterial cell's DNA is not surrounded by a nuclear envelope, __________ occur(s).

coupled transcription and translation

The function of tRNA during protein synthesis is to __________.

deliver amino acids to their proper site during protein synthesis

If the sequence ATGCATGTCAATTGA were mutated such that a base were inserted after the first G and the third T were deleted, how many amino acids would be changed in the mutant protein?

two codons would be changed the old codon ATG CAT GTC AAT TGA would now be ATG*XCA TGC *AAT TGA

wobble -

due to coding - this explains why the synonymous codons for a given amino acid most often differ in their their nucleotide base but not in other bases

The TATA box is a __________ that allows for the binding of __________ and __________.

eukaryotic promoter; transcription factors; RNA polymerase II In eukaryotes, a collection of proteins called transcription factors mediate the binding of RNA polymerase and the initiation of transcription. Only after transcription factors are attached to the promoter does RNA polymerase II bind to it. The whole complex of transcription factors and RNA polymerase II bound to the promoter is called a transcription initiation complex. This figure shows the roles of transcription factors and a crucial promoter DNA sequence called a TATA box in forming the initiation complex at a eukaryotic promoter.

The RNA segments joined to one another by spliceosomes are _____.

exons The splicesomes cut out non coding portions called *introns* and join together the remaining pieces together which are called *exons* -Exons are expressed regions. -Translation takes place in the cytoplasm in *ribosomes*

True or false? A codon is a group of three bases that can specify more than one amino acid.

false; a codon can only code for one specific amino acid

steps of translation

first the small cap of the ribosome will bind to the mRNA molecule at the 5 prime side -the anticodon will bind to the starting codon in the mRNA -this initiator will be methionine -initiation factors work together to bring the large cap of the ribosome together to form the *initiation complex* -from here translation can begin a the following peptides will be added in the A site and shuffled along -a part in the ribosome will form a peptide bond between the new peptide that have been added to the chain

The flow of information in a cell proceeds in what sequence?

from DNA , (transcription)to RNA (RNA processing), to protein (translation)

Polysomes may be defined as __________

groups of ribosomes

The bonds that hold tRNA molecules in the correct three-dimensional shape are __________.

hydrogen bonds similar to how proteins are held together in their three dimensional shape

Where does translation take place?

in a ribosome, in the cytoplasm

transcription factors

in eukaryotes there is a special collection of proteins called transcription factors that mediate the binding of NRA polymerase and the initiation of transcription -these are required to be attached to the promoter for RNA polymerase II to even bind to the promoter. Once these are all present only then can the RNA polymerase bind and when they do bind it forms a complex called *transcription initiation complex*

TATA box

in the eukaryotic promoter a crucial promoter DNA sequence called TATA box is usually present in forming the initiation complex at a eukaryotic promoter

translation takes place in three phases

initiation elongation termination

The type of point mutation that results in a premature stop codon is called a _________ mutation.

nonsense

By bombarding the fungus Neurospora crassa with X-rays, Beadle and Tatum were able to study __________ and characterize enzymes in a __________.

nutritional mutants ; biochemical pathways

polysomes aka polyribosomes

once a peptide chain is far enough through the first ribosome it can enter a second one and begin making another polypeptide simultaneously -

stop codon

one of the few stop codons will call for a 'release factor' to come and break off the polypeptide chain ( protein formed) and disassemble the process from here

mutagens

physical and chemical agents that interact with DNA in ways that cause mutations -xrays

One strand of a DNA molecule has the following sequence: 3-AGTACAAACTATCCACCGTC-5. In order for transcription to occur in that strand, there would have to be a specific recognition sequence, called a(n) __________, to the left of the DNA sequence indicated.

promoter

Define the following processes / areas in the picture

promoter RNA polymerase process promoter is the green area the starting area of transcription The grey area is the RNA polymerase process

what is the most abundant form of RNA?

rRNA was once known to be the key component of the structural of ribosomes, but its actually found to be a catalytic element for protein synthesis. It is the most abundant type of RNA (about 80%) in the cell. rRNA is comprised of a large and small subunit. The cell uses three different types of RNAs to build proteins. rRNA is part of the ribosome, which is the site of protein synthesis. mRNA carries the genetic information from the DNA; the information specifies the sequence of amino acids in the new protein. tRNA interprets the information from the mRNA and brings the appropriate amino acids to the ribosome.

Beadle and Tatum

works with bread mold ; hit the bread with x rays to demonstrate genetic changes -due to their experiments and being able to isolate growth to a bread with a certain amino acid they were able to also support the one gene -one enzyme hypothesis- meaning the function of a gene is to produce an enzyme -reveiwed their definition later to maybe suggest one gene - one protein since not all have to be enzymes , such as keratin - a structural protein

rRNA

ribosomal RNA - made in the nucleolus -they are processed and assembled in with proteins and then when complete passed through nuclear pores into the cytoplasm -rRNA is the most abundance RNA in the cell

targeting polypeptide to specific locations

ribosomes are all the same and can either be used as bound ribosomes or free ribosomes they are all the same effectively except bound ribosomes are marked at the beginning with a signal called *signal peptide* - this marks those ribosomes bound for the ER system -from here a *signal recognition particle * SRP will pick up the ribosome and take it to its spot on the ER -these signal peptides mark the ribosomes for their locations and they follow the same processes - this SRP will take the entire ribosome over to its specific location, let it produce the polypeptide chain into the desired location then disassemble from there

there are two types of small scale mutations

single nucleotide pair substitutions or additions and deletions

In eukaryotic cells, a __________ by a __________ targets a growing peptide to the endoplasmic reticulum.

single peptide ; signal recognition particle

Spliceosomes are composed of _____.

snRNPs and other proteins snrps do the cutting and mending while proteins hold the structure

missense mutations

substitutions that change one amino acid to another -may have little affect as the new amino acid could potentially have similar properties as the original or may be in a region of the protein where the exact sequence of amino acids is not essential for protein function -it still makes sense and operates or works just not in the exact right sense

An exception to the one gene-one enzyme hypothesis is __________.

that not all genes code for enzymes; some genes code for structural proteins such as keratin

Eukaryotic processing of the primary transcript includes __________. This refers to the alteration of mRNA before is able to leave the nucleus

the addition of a 5ꞌ cap, a 3ꞌ poly-A tail, and the splicing out of introns

Bacteria can transcribe and translate human genes to produce functional human proteins because __________.

the genetic code generally universal The genetic code is nearly universal, shared by organisms from the simplest bacteria to the most complex plants and animals. The RNA codon CCG, for instance, is translated as the amino acid proline in all organisms whose genetic code has been examined. Exceptions to the universality of the genetic code include translation systems in which a few codons differ from the standard ones. Slight variations in the genetic code exist in certain unicellular eukaryotes and in the organelle genes of some species. Despite these exceptions, the evolutionary significance of the code's near universality is clear. A language shared by all living things must have been operating very early in the history of life—early enough to be present in the common ancestor of all present-day organisms. A shared genetic vocabulary is a reminder of the kinship that bonds all life on Earth.

ribosome sites

the p site holds the part of the polypeptide chain that is currently being added to or growing

Anticodon

the particular nucleotide triplet that base pairs to a specific mRNA codon -these are held at one end of a of a tRNA which is shaped like a clover leaf toward the bottom and overall like a large L shape

Gene expression is _____

the process by which DNA directs the synthesis of proteins

gene expression

the process by which DNA directs the synthesis of proteins ( in some cases just RNAs). The expression of genes that code for proteins include two stages ; transcription and translation

__________ is the synthesis of RNA using information in the DNA.

transcription

Getting information from DNA to protein involves two major steps which are ;

transcription and translation

__________ is the synthesis of a polypeptide using information in the mRNA.

translation

Stop codons

UAG UAA UGA

At which site do new aminoacyl tRNAs enter the ribosome during elongation?

A site This is the site at which new aminoacyl tRNAs that are complementary to the mRNA codon enter the ribosome. The P site is where the growing polypeptide chain is held The A site hold the next the tRNA that will add the next amino acid to be added to the chain. The E site ( exit site) allowing discharged tRNAs to exit the ribosome

Which mutation(s) would not change the remainder of the reading frame of a gene sequence that follows the mutation(s)?

An addition and a deletion could potentially not affect any of the codons This combination results in no net change in the number of bases, so the reading frame would eventually be restored.

one gene one enzyme hypothesis

Archibald Garrod - a gene dictates the productions of a specific enzyme

what is the difference in the transcription/ translation process in eukaryotic cells and bacterial cells?

Bacterial cells do not posses a membrane bound nucleus. This is the main difference. - in a eukaryotic cell transcription takes place inside the nucleus then the mRNA is transported to the cytoplasm where translation occurs. -the mRNA must be modified to its final state before it can exit the nucleus to start translation -in Eukaryotic cells the mRNA can exist in *primary transcript* in which the RNA is not translated to protein

What determines which base is to be added to an RNA strand during transcription?

Base pairing between the DNA template strand and the RNA nucleotides Transcription involves the formation of an RNA strand that is complementary to the DNA template strand.

Who formulated the one gene-one enzyme hypothesis?

Beadle and Tatum formulated the one gene-one enzyme hypothesis. Beadle and Tatum worked with a bread mold called Neuropora that they had bombarded with X-rays resulting in mutants. Because each mutant was defective in a single gene, Beadle and Tatum saw that, taken together, the collected results provided strong support for a working hypothesis they had proposed earlier. The one gene-one enzyme hypothesis, as they dubbed it, states that the function of a gene is to dictate the production of a specific enzyme. Further support for this hypothesis came from experiments that identified the specific enzymes lacking in the mutants. Beadle and Tatum shared a Nobel Prize in 1958 for "their discovery that genes act by regulating definite chemical events" (in the words of the Nobel committee).

What is a key difference in gene expression between eukaryotic and prokaryotic cells?

In prokaryotic cells, the mRNA transcript is immediately available as mRNA without processing. in eukaryotic the mRNA has to be modified before it is ready to move out of the nucleus into the cytoplasm for translation

Insertions and deletions are called __________ mutations.

Insertions and deletions are called frameshift mutations. Insertions and deletions are additions or losses of nucleotide pairs in a gene. These mutations have a disastrous effect on the resulting protein more often than substitutions do. Insertion or deletion of nucleotides may alter the reading frame of the genetic message, the triplet grouping of nucleotides on the mRNA that is read during translation. Such a mutation occurs whenever the number of nucleotides inserted or deleted is not a multiple of three. All nucleotides downstream of the deletion or insertion will be improperly grouped into codons; the result will be extensive missense, usually ending sooner or later in nonsense and premature termination. Unless the frameshift is very near the end of the gene, the protein is almost certain to be nonfunctional.

Where does RNA polymerase begin transcribing a gene into mRNA?

It starts after a certain nucleotide sequence called a promoter. In both eukaryotes and prokaryotes, RNA polymerase binds to the gene's promoter and begins transcription at a nucleotide known as the start point, although in eukaryotes the binding of RNA polymerase to the promoter requires transcription factors.

What amino acid sequence does the following DNA nucleotide sequence specify? 3′−TACAGAACGGTA−5′ Express the sequence of amino acids using the three-letter abbreviations, separated by hyphens (e.g., Met-Ser-His-Lys-Gly).

Met-Ser-Cys-His First notice the DNA sequence is running 3-5 when transcription happens it will always match up with the side that is running 5-3 so we have to complete this sequence. -for 3′−TACAGAACGGTA−5′ the matching side is ATGTCTTGCCAT , then translate this to RNA (change all the Ts to Us) AUGUCUUGCCAU -This mRNA code could be translated to the follow amino acid sequences which code for what is listed as the answer Before mRNA can be translated into an amino acid sequence, the mRNA must first be synthesized from DNA through transcription. Base pairing in mRNA synthesis follows slightly different rules than in DNA synthesis: uracil (U) replaces thymine (T) in pairing with adenine (A). The codons specified by the mRNA are then translated into a string of amino acids.

Genes provide the instructions for making specific proteins but do not directly build a protein. What is responsible as the bridge between DNA and protein synthesis?

RNA chemically similar to DNA however RNA contains Ribose instead of deoxyribose and contains the sugar uracil instead of thymine RNA = GC , AU RNA is single stranded

Genetic information of eukaryotic cells is transferred from the nucleus to the cytoplasm in the form of __________.

RNA mRNA to be exact

one of the strands of DNA double helix that are separated are selected as the Template strand. What is the other strand called?

The non template strand This are somewhat selected at random ( which strand to use as the template) Just RNA polymerase must transcript in the 5'-3' direction

Which of the following statements best describes the promoter of a protein-coding gene?

The promoter is a nontranscribed region of a gene The promoter is the regulatory region of a protein-coding gene at which RNA polymerase must bind to initiate transcription—it is not transcribed into the RNA.

Which of the following best describes the arrangement of genetic information in a DNA molecule?

The response the three-nucleotide words of a gene are arranged in a nonoverlapping series on the DNA template strand best describes the arrangement of genetic information in a DNA molecule. The genetic instructions for a polypeptide chain are written in the DNA as a series of nonoverlapping, three-nucleotide words. The series of words in a gene is transcribed into a complementary series of nonoverlapping, three-nucleotide words in mRNA, which is then translated into a chain of amino acids.

What is meant by translocation?

The ribosome slides one codon down the mRNA. Translocation is the process by which the ribosome slides down the mRNA so a new cycle of elongation can begin.

Transcription begins at a promoter. What is a promoter?

This is the site where the RNA polymerase must bind to initiate transcription The DNA sequence where RNA polymerase attaches and initiates transcription is know as the promoters; and in bacteria the sequence that signals the end of transcription is called the *terminator* the direction of transcription from the 5'-3' directions is considered 'downhill' while the other directions is referred to as 'uphill'

What name is given to the process in which a strand of DNA is used as a template for the manufacture of a strand of pre-mRNA?

Transcription is the process by which a DNA template is used for the manufacture of several different types of RNA. this is the first step in the process of forming a new polypeptide

What name is given to the process in which the information encoded in a strand of mRNA is used to construct a protein?

Translation is the process by which information encoded in RNA is used to manufacture a polypeptide. this is the third step in the transcription / translation process

When RNA is being made, the RNA base _________ always pairs with the base __________ in DNA.

U; A it specifically asks which RNA base matches up with DNA

If a mutated DNA sequence produces a protein that differs in one central amino acid from the normal protein, which of the following kinds of mutations could have occurred?

a deletion and an addition to the same codon If the mutations occur within the same codon, only that codon (amino acid) will be altered.

Generally speaking, which of the following mutations would most severely affect the protein coded for by a gene?

a frameshift deletion at the beginning of the gene A frameshift mutation at the beginning of a gene would affect every codon after the point where the mutation occurred. During protein synthesis, incorrect amino acids would be inserted from the point where the frameshift mutation occurred on; the resulting protein would most probably be nonfunctional. For this reason, a frameshift mutation at the beginning of a gene is generally the most severe type of mutation.

gene def; summary

a gene is a region of DNa that can be expressed to produce a final functional product that is either a polypeptide or an RNA molecule

splicesome

a large complex of made of proteins and small RNAs called a spliceosome that facilitate the removal of introns -it binds to several short nucleotide sequences along an intron but not only splices but also acts as a catalyst for the process

During RNA processing a(n) _____ is added to the 3' end of the RNA.

a long string of adenine nucleotides A poly-A tail is added to the 3' end of the RNA.

nonsense mutations

a point mutation where the change in the codon calls for a stop codon in which it will be shorter than normal -usually results in a dysfunctional polypeptide chain

Which of the following mutations would be most likely to have a harmful effect on an organism? a nucleotide-pair substitution a single nucleotide deletion near the end of the coding sequence a single nucleotide insertion downstream of, and close to, the start of the coding sequence a deletion of three nucleotides near the middle of a gene a single nucleotide deletion in the middle of an intron

a single nucleotide insertion downstream of, and close to, the start of the coding sequence

insertions and deletions frameshift mutation

additions or losses of nucleotide pairs in a gene -theses can have a disastrous effect on the resulting protein more than substitutions do - if a total of three genes are not inserted and deleted together can cause the whole reading frame of the genetic message to change -frame shift mutation - occurs whenever the number of nucleotides inserted or deleted is not a multiple of three and all nucleotides downstream of the deletion of insertion will be improperly grouped into codons- could cause extensive missense -Unless frameshift is near the very end of the gene the protein is almost certain to be nonfunctional

gene expression summarized

biochemistry holds that information flows from DNA to RNA to protein. The process of making protein from the mRNA is called translation. Translation is carried out by the ribosome, which binds to the mRNA and binds tRNA, which recognizes the codons on the mRNA and brings the appropriate amino acid with it. The ribosome forms the peptide bond between the new amino acid and the growing peptide chain.

point mutations

changes in a single nucleotide pair of a gene -occurs in the gamete or in a cell that gives rise to gametes -if the mutation has an adverses effect on the phenotype of a person the mutant condition is referred to as a genetic disorder or hereditary disease -sickle cell anemia is an example of this

Which of the following terms best describes the relationship between the newly synthesized RNA molecule and the DNA template strand?

complementary Because the template strand determines the nucleotides to be added to the RNA strand, using the same complementarity rules of the DNA, they will be complementary to each other.

translation

loose definition - the synthesis of a polypeptide chain of which is broken down into three stages ; initiation, elongation and termination -polypeptides always synthesized in one direction from the N terminus (the methionine start codon) toward the c terminus at the end called the C terminus -the adding of the next amino acid required hydrolysis as a form of energy -when the stop codon enters the A site ( first site) a release factor will enter the A site and the chain will break off at the e site and the ribosome will disassemble . The release factors put off water as a by product

Which nucleic acid is translated to make a protein? DNA tRNA rRNA mRNA

mRNA mRNA is the message that is translated to make a protein.

alternative gene splicing

many genes are known to give rise to two or more different polypeptides, depending on which segments are treated as exons during RNA processing -meaning depending on which ones are left out a thymine could be the beginning or end of a amino acid that gets coded

post translational modification

many times polypeptides or proteins are not functional straight out of the ribosome or translation - can have one or more amino acids from the leading end of the chain removes -could be cleaved in two or more -

mRNA

messenger RNA , the RNA molecule that carries genetic messages from DNA to the protein synthesizing machinery of the cell - the mRNA provides the information for translation

In addition, one codon (shown in blue) codes for the amino acid __________ and functions as a "start" signal.

methionine AUG Nearly every mRNA gene that codes for a protein begins with the start codon, AUG, and thus begins with a methionine. Nearly every protein-coding sequence ends with one of the three stop codons (UAA, UAG, and UGA), which do not code for amino acids but signal the end of translation.

The sickle-cell β-globin mutation is an example of a __________.

missense mutation

During RNA processing a(n) _____ is added to the 5' end of the RNA.

modified guanine nucleotide The 5' cap consists of a modified guanine nucleotide. the 5' cap consists of a modified guanine nucleotide

Starting transcripiton

the promoter of a gene includes within it the *transcription starting point* ( the actual single nucleotide where RNA synthesis actually starts) and typically extends several dozen or more nucleotide pairs upstream from the starting point -RNA polymerase binds ina precise location and orientation on the promoter, determining where transcription starts and which of the two stands of the DNA hell is used as the template -certain sections of a promoter are especially important for binding RNA polymerase.

nucleotide pair substitutions

the replacement of one nucleotide and its partner -because several different nucleotide can all code for the same amino acid -When the same amino acid is inserted and there are no observable differences in the phenotype this is known as a *silent mutation*

transcription unit

the strand of DNA to be downstream from the promoter ( the beginning of a DNA strand) that is transcribed into an RNA molecule

transcription

the synthesis of RNA using information from DNA -the information is rewritten or transcribed from DNA to RNA -DNA strand provides a template for making new complementary strand during DNA replication

Translation

the synthesis of a polypeptide ( made of many amino acids to form polypeptide chains // aka proteins) -cell must translate the nucleotide sequence of an mRNA molecule into amino acid sequence of a polypeptide -this takes place in a *ribosome* -Ribosomes - which are molecular complexes that facilitate the orderly linking of amino acids into polypeptide chains -transcription and translation take place in all organisms , even those without membrane bound nucleus

RNA processing

this is the process in eukaryotic cells that takes place on pre mRNA before it can leave the nucleus where both ends of the primary transcript are alters and certain interior sections of the RNA ( introns) are cut out and the remaining parts (exons) are spliced together 3 items . splicing of introns , and poly a tail and 5 cap (G) The 5' end receives a 5' cap - a modified form of guanine nucleotide after transcription for the first 20-40 nucleotides has taken place The 3 ' end gets a *polyAcap* which is a line of 50-250 Adenine nucleotide

A codon consists of _____ bases and specifies which _____ will be inserted into the polypeptide chain.

three ; amino acids Three nucleotide bases make up a codon and specify which amino acid comes next in the sequence. Each codon can be different but still code technically for the same thing

The "triplet code" refers to the fact that _________.

three nucleotides code for a single amino acid

what is the primary job of tRNA ?

to match up RNA bases with the correct amino acids in a ribosome