CELL BIO EXAM 3 CHAPTER 7

polyribosomes (also known as polysomes)

these large cytoplasmic assemblies are made up of many ribosomes spaced as close as 80 nucleotides apart along a single mRNA molecule

What does it mean for a mature mRNA to be "export ready"?

these proteins include poly-A-binding proteins, a cap-binding complex, and proteins that bind to mRNAs that have been appropriately spliced.

ESSENTIAL CONCEPT #3 FROM BOOK

Cells make several functional types of RNAs, including messenger RNAs (mRNAs), which carry the instructions for making proteins; ribosomal RNAs (rRNAs) which are the crucial components in ribosomes; and transfer RNAs (tRNAs), which act as adaptor molecules in protein synthesis.

When does the DNA template and the newly made RNA get released?

Chain elongation continues until the enzyme encounters a second signal in the DNA, the terminator (or stop site), where the polymerase halts and releases both the DNA template and the newly made RNA transcript

What are the different lifetimes controlled by?

Controlled by nucleotide sequences in the mRNA itself, called the 3' untranslated region, which lie between the 3' end of the coding sequence and the poly-A tail.

How do proteosomes select which proteins in the cell should be degraded?

In eukaryotes, proteasomes act primarily on proteins that have been marked for destruction by the covalent attachment of a small protein called ubiquitin. These ubiquitylated proteins are recognized, unfolded and fed into the proteasome

What is known as the "central dogma"?

The flow of genetic information from DNA to RNA (transcription) and from RNA to protein (translation) occurs in all living cells. -Francis Crick

ESSENTIAL CONCEPT #1 FROM BOOK

The flow of genetic information in all living cells is DNA --> RNA --> protein. The conversion of the genetic instructions in DNA into RNAs and proteins is termed GENE EXPRESSION

The recognition of a codon by the anticodon on a tRNA molecule depends on what?

depends on the same type of complementary base-pairing used in DNA replication and transcription.

How does the "sigma factor" recognize the promoter region without seeing the interior of the DNA double helix where the base pairs are located?

each base presents unique features to the outside of the double helix, allowing the sigma factor to find the promoter sequence without having to separate the entwined DNA strands.

ribosome

"the molecular machine" that can move along the mRNA, capture complementary tRNA molecules, hold the tRNAs in position, and covalently link the amino acids that they carry to form a polypeptide chain. -this large complex of a ribosome is made from dozens of ribosomal proteins and ribosomal RNAs (rRNAs)

Eukaryotic Gene Transcription (differing eukaryotes from bacteria)

#1. Bacteria contain a single type of RNA polymerase while Eukaryotes have RNA polymerase I, RNA polymerase II, and RNA polymerase III that are all responsible for transcribing different types of genes. #2. whereas the bacterial RNA polymerase (along with its sigma subunit) is able to initiate transcription on its own, eukaryotic RNA polymerases require the assistance of a large set of accessory proteins, called general transcription factors. #3. In bacteria, genes tend to lie very close to one another in the DNA, with only very short lengths of nontranscribed DNA between them. But in plants and animals, including humans, individual genes are spread out along the DNA, with stretches of up to 100,000 nucleotide pairs between one gene and the next. #4. Eukaryotic transcription initiation must take into account the packing of DNA into nucleosomes and more compact forms of chromatin structure

What happens to make a peptide bond form?

(2) the small ribosomal subunit loaded with the initiator tRNA and translation initiation factors bind to the 5' end of an mRNA molecule, which marked by the 5' cap . (3) the small ribosomal subunit moves from 5' to 3' along the mRNA searching for the first AUG codon. (4) when the AUG is encountered and recognized by the initiator tRNA, the initiation factors dissociate away, to make way for the large ribosomal subunit to bind to it. (because the initiator tRNA is bound to the P site, protein synthesis is ready to begin with the addition of the next charged tRNA to the A site)

"wobble" base pairing

*Some amino acids have more than one tRNA, and some tRNAs are constructed so that they require accurate base-pairing only at the first two positions of the codon and can tolerate a mismatch (or wobble) at the third position. This wobble base-pairing explains why so many of the alternative codons for an amino acid differ only in their third nucleotide

Where is a bacterial cell's DNA found vs eukaryotic cell's DNA?

*nucleoid region; bacterial DNA lie directly exposed to the cytoplasm, which contains the ribosomes on which protein synthesis takes place. *in eukaryotic cells, DNA is enclosed within the nucleus, where transcription takes place, as protein synthesis takes place on ribosomes in the cytoplasm.

Proteosomes

*only in eukaryotic cells *large protein machines that break down proteins that are present in both the cytosol and the nucleus

What types of proteins are identfied to be ubiquitylated and degraded in the proteosome?

*proteins that are meant to be short-lived that contain a short amino acid sequence that identifies as needed to be ubiquitylated *damaged or misfolded proteins *proteins containing oxidized or abnormal amino acids

Functions of proteolytic pathways?

*to rapidly degrade those proteins whose lifetimes must be kept short *recognize and remove proteins that are damaged or misfolded (critical because improperly folded proteins tend to aggregate, triggering cell death)

what are translation initiation factors in eukaryotes

- (1) an initiator tRNA, charged with methionine, is first loaded into the P site of the small ribosomal subunit, along w additional proteins called TRANSLATION INITIATION FACTORS, mRNA is also bound *only a charged initiator tRNA molecule is capapble of binding tightly to the P site in the absense of the large ribosomal subunit.

Difference between DNA and RNA polymerase?

- RNA polymerase uses ribonucleoside for phosphates as substrates, so it catalyzes the linkage of ribonucleotides, not deoxyribonucleotides -RNA polymerases can start an RNA chain without a primer - RNA polymerases make about one mistake for every 10^4 nucleotides copied into RNA, whereas DNA polymerase makes only one mistake for every 10^7 nucleotides copied.

tRNA folding

-4 short segments of the folded tRNA are double helical, producing a cloverleaf shaped molecule. (for ex. a 5' - GCUC- 3' sequence in one part of the polynucleotide chain can base pair with 5' - GAGC - 3' sequence in another region of the same molecule.) The cloverleaf undergoes further folding to form a compact, L-shaped structure that is held by hydrogen bonds bt different regions of the molecule.

How is a prokaryotic ribosome different from a eukaryotic ribosome?

-a prokaryotic ribosome can readily bind directly to a start codon that lies in the interior of an mRNA, as long as a ribosome-binding site precedes it by several nucleotides. -a eukaryotic mRNA usually carries the information for a single protein

the mechanism for selecting a start codon is different in bacteria.....

-bacterial mRNAs have no 5' caps -instead, they contain specific ribosome-binding sequences, up to six nucleotides long, that are located a few nucleotides upstream of the AUGs at which translation is to begin

eukaryotic and prokaryotic ribosomes

-both are composed of one large subunit and one small subunit, which fit together to form a complete ribosome **the small ribosomal subunit matches the tRNAs to the codons of the mRNA, while the large subunit catalyzes the formation of the peptide bonds that covalently link the amino acids together into a polypeptide chain. these two subunits come together on an mRNA molecule near its 5′ end to start the synthesis of a protein.

The orientation of the promoter determines what?

-determines what direction a gene is transcribed and what strand of the 2 DNA strands is the template strand

How does the RNA polyerase know which of the two DNA strands to use as the template for transcription?

-every promoter has a certain polarity (it contains two different nucleotide sequences upstream of the transcriptional start site that position the RNA polymerase, ensuring that it binds to the promoter in only one orientation) - Because the polymerase can only synthesize RNA in the 5′-to-3′ direction once the enzyme is bound it must use the DNA strand oriented in the 3′-to-5′ direction as its template.

(cont'd)

-the mRNA is then pulled through the ribosome like a long piece of tape. As the mRNA inches forward in a 5′-to-3′ direction, the ribosome translates its nucleotide sequence into an amino acid sequence, one codon at a time, using the tRNAs as adaptors. each amino acid is thereby added in the correct sequence to the end of the growing polypeptide chain

What is an advantage that DNA has over RNA?

1) the double-helical structure of DNA and the 2) use of thymine rather than uracil—further enhanced 3) DNA stability (dna is more stable) by making the molecule easier to repair.

How does the lariat structure form?

1. branchpoint adenine, with a 2' OH- group attatched, in the intron sequence attacks the 5' splice site and cuts the sugar-phosphate backbone of the RNA. 2. the cut 5' end of the intron becomes covalently bonded to the 2' OH-group of the ribose A nucleotide, cuasing the to form a loop- branched structure. 3. the free 3'-OH bonded end of the exon sequence then deattaches and becomes the lariat structure, ready to react with the start of the next exon sequence. 4. this lariat structure is eventually degraded in the nucleus.

Steps to add an amino acid to a growing polypeptide chain (this cycle of reactions is repeated each time an amino acid is added to the polypeptide chain, with the new protein growing from its amino to its carboxyl end until a stop codon in the mRNA is encountered.)

1. the appropriate charged tRNA enters the A site by base-pairing with the complementary codon on the mRNA molecule. 2. its amino acid is then linked to the peptide chain held by the tRNA in the neighboring P site. 3. the large ribosomal subunit shifts forward, moving the tRNA to the E site before ejecting it

What forms the catalytic site for peptide bond formation, outside of the A, P, and E sites?

23S rRNA of the large subunit

RNA polymerase always moves in what direction?

3' -----> 5'

the average sized protein has a mass of how many daltons

30,000 daltons

What is the proteosome consist of?

A proteasome contains a central cylinder formed from proteases whose active sites face into an inner chamber. Each end of the cylinder is stoppered by a large protein complex formed from at least 10 types of protein subunits. These protein stoppers bind the proteins destined for degradation and then—using ATP hydrolysis to fuel this activity—unfold the doomed proteins and thread them into the inner chamber of the cylinder

What three sites does the ribosome contain for tRNA molecules

A site, P site, and E site

Difference between how proteins are encoded in bacteria vs. eukaryotes

BACTERIA most proteins are encoded by an uninterrupted stretch of DNA sequence that is transcribed into an mRNA that, without any further processing, can be translated automatically into a protein. EUKARYOTES -most eukaryotic pre-mRNAs have to undergo more processing before they are functional mRNAs; most protein-coding eukaryotic genes have their coding sequences interrupted by long, noncoding, intervening sequences called INTRONS.

mRNA molecules are eventually degraded in the cytosol (specificity)

Each mRNA molecule is eventually degraded into nucleotides by ribonucleases (RNAses) present in the cytosol, but the lifetimes of mRNA molecules differ considerably—depending on the nucleotide sequence of the mRNA and the type of cell. (in bacteria, most mRNAs are degraded rapidly) (3 minute lifetime in bacteria and 30 min-10 hours in eukaryotes)

RNA polymerase

Enzyme that links together the growing chain of ribonucleotides during transcription, catalyzing the formation of the phosphodiester bonds that form the sugar-phosphate backbone of the RNA chain. The RNA polymerase moves stepwise along the DNA, unwinding the DNA helix for complementary base pairing.

messanger RNA (mRNA) in eukaryotes vs. bacteria?

Eukaryotes: each mRNA carries information transcribed from just one gene, which codes for a single protein Bacteria: a set of adjacent genes is often transcribed as a single mRNA, which therefore carries the information for several different proteins.

ESSENTIAL CONCEPT #7 FROM BOOK

Eukaryotic pre-mRNAs go through several RNA processing steps before they leave the nucleus as mRNAs, including 5' RNA capping and 3' polyadenylation. THese reactions, along with splicing, take place as the pre-mRNA is being transcribed.

How eukaryotic RNA polymerase II begins transcription (and its general transcription factors)

First.... - The TATA box, about 25 nucleotides upstream from the transcription start site, contain a DNA sequence of primarily T and A nucleotides Second.... -The TFIID (another transcription factor), with its TBP (TATA-binding protein) attatched, binds to the TATA box and bends the DNA double helix. Third.... - the binding of TFIID enables the adjacent binding of TFIIB (another transcription factor) to the TFIID, now causing the RNA polymerase to assemble at the promotor. Fourth.... -TFIIH then pries apart the double helix at the transcription start point, using energy of ATP hydrolysis, which then exposes the template strand of the gene. Fifth.... -TFIIH phosphorylates the RNA polymerase II to its "tail", releasing the polymerase from the general transcription factors so it can begin transcription (the site of phosphorylation is a long polypeptide tail that extends from the polymerase). Lastly.... -When RNA polymerase II finishes transcribing a gene, it too is released from the DNA; the phosphates on its tail are stripped off by protein phosphatases, and the polymerase is then ready to find a new promoter. Only the dephosphorylated form of RNA polymerase II can initiate RNA synthesis.

ESSENTIAL CONCEPT #15 FROM BOOK

From our knowledge of present-day organisms and the molecules they contain, it seems likely that life on Earth began with the revolution of RNA molecules that could catalyze their own replication.

Where must the general transcription factor assemble before beginning transcription?

General transcription factors must assemble at each promoter, along with the polymerase, before the polymerase can begin transcription.

What does controlling the breakdown of proteins into their amino acids help with?

Helps cells regulate the amount of each particular protein

ESSENTIAL CONCEPT #6 FROM BOOK

Introns are removed from the RNA transcripts in the nucleus by RNA splicing, a reaction catalyzed by small ribonucleoprotein complexes known as snRNPs. Splicing removes the introns from the RNA and joins together the exons-often in a variety of combonations, allowing multiple proteins to be produced from the same gene.

RNA splicing (occurs after capping)

Introns are removed from the newly synthesized RNA and the exons are stitched together; each transcript receives a poly-A tail. Once a transcript has been spliced and its 5' and 3' ends have been modified, the RNA is now a functional mRNA that can leave the nucleus and be translated into protein.

ESSENTIAL CONCEPT #16 FROM BOOK

It has been proposed that RNA served as both the genome and the catalysts in the first cells, before DNA replaced RNA as a more stable molecule for storing genetic information, and proteins replaced RNAs as the major cataytic and structural components. RNA catalysts in modern cells are thought to provide a glimpse into an ancient

ESSENTIAL CONCEPT #5 FROM BOOK

Most protein-coding genes in eukaryotic cells are composed of a number of coding regions, called exons, interspersed with larger noncoding regions, called introns. When a eukaryotic gene is transcribed from DNA into RNA, both the exons and the introns are copied.

What are nuclear pore complexes and what are allowed to go through them?

Nuclear pore complexes connects the nucleoplasm with the cytosol. They act as gates that control which macromolecules can enter or leave the nucleus and only correctly processed mRNAs can be exported.

What happens once the proteins are inside the chamber?

Once the proteins are inside, proteases chop them into short peptides, which are then dropped from either end of the proteasome. Housing proteases inside these molecular destruction chambers makes sense, as it prevents the enzymes from running/spreading in the cell.

QUIZ Q #10 A major difference between eukaryotic and prokaryotic gene expresison is:

Prokaryotes do not have a separate nucleus

ESSENTIAL CONCEPT #12 FROM BOOK

Protein synthesis begins when a ribosome assembles at an initiation codon (AUG) in an mRNA molecule, a process that depends on proteins called translation initiation factors. The completed protein chain is released from the ribosome when a stop codon (UAA,UAG, OR UGA) in the mRNA is reached.

QUIZ Q #1 What is the principal consitutient of cells?

Proteins

QUIZ Q #14 What might have been the original biological molecule?

RNA

What are exons?

Scattered pieces of coding sequence that are shorter than introns (introns range from 1 to 10,000 nucleotides)

DNA and RNA similarities and differences

Similiarities: both are linear polymers made of 4 different nucleotide sub-units, linked together by phosphodiester bonds Differences: DNA: dexoyribose sugar, ACGT, double stranded RNA: ribose sugar, ACGU, single stranded, shorter than DNA

ANTIBIOTICS THAT INHIBIT BACTERIAL PROTEIN OR RNA SYNTHESIS

TETRACYCLINE: blocks binding of aminoacyl-tRNA to A site of ribosome (the first step) STREPTOMYCIN: prevents the transition from initiation complex to chain elongation of polypeptides; also causes miscoding CHLORAMPHENICOL: blocks the peptidyl transferase reaction on ribosomes (step 2) CYCLOHEXIMIDE: blocks the translocation reaction on ribosomes (step 3) RIFAMYCIN: blocks initiation of transcription by binding to RNA polymerase

ESSENTIAL CONCEPT #14FROM BOOK

The concentration of a protein in a cell depends on the rate at which the mRNA and protein are synthesized and degraded. Protein degradation in the cytosol and nucleus occurs inside large protein complexes called proteasomes.

ESSENTIAL CONCEPT #10 FROM BOOK

The correspondence between amino acids and codons is specified by the genetic code. The possible combinations of the 4 different nucleotides in RNA gives 64 different codons in the genetic code. Most amino acids are specified by more than one codon.

What do the different lifetimes of mRNAs help with?

The different lifetimes of mRNAs help the cell control the amount of each protein that it synthesizes (proteins made in large amounts, such as beta globulin) are translated from mRNAs that have long lifetimes, whereas proteins made in smaller amounts, or whose levels change rapidly in response to signals, are synthesized from short-lived mRNAs.

ESSENTIAL CONCEPT #9 fROM BOOK

The nucleotide sequence in mRNA is read in sets of three nucleotides called codons; each codon corresponds to one amino acid.

QUIZ Q #2 In RNA,

The nucleotides are ribonucleotides

QUIZ Q #6 What would happen if you reversed the order of the bacterial promoter elements?

The polymerase would transcribe upstream instead of downstream.

What is the promoter?

The promoter contains the specific sequence of nucleotides that lies immediately upstream of the starting point for RNA synthesis (so the RNA polymerase can open up the DNA double helix immediately in front of the promoter)

what does this reaction produce

The reaction produces a high-energy bond between the charged tRNA and the amino acid.

ESSENTIAL CONCEPT #13 FROM BOOK

The stepwise linking of amino acids into a polypeptide chain is catalyzed by an rRNA molecule in the large ribosomal subunit, which thus acts as a ribozyme.

QUIZ Q #3 When making RNA, the sequence of the RNA chain is determined by complementary base pairing with:

The template DNA strand

Some of the pre-mRNA transcripts synthesized are mature mRNAs that are useful to the cell; the rest (excised introns, broken RNAs, and spliced transcripts) could be dangerous to the cell if allowed to leave the nucleus. How does the cell distinguish amongst the rare, mature mRNA needed to be exported to the cytosol versus the "debris" left over?

The transport of mRNA from the nucleus to the cytosol (where mRNAs are translated into protein) is highly selective (only mRNAs can go through the nuclear pore complexes). The "waste RNAs" remain behind in the nucleus to be degraded there, and their nucleotide building blocks are reused for transcription.

QUIZ Q #5 In gene expression, a difference between expressing for the final product to be protein vs RNA is...

When an RNA is the final product, there is no need for a translation step.

What is the function of general transcription factors?

They are accessory proteins that assemble on the promoter, where they position the RNA polymerase and pull apart the DNA double helix to expose the template strand, allowing the polymerase to begin transcription. (similiar function of a sigma factor in bacterial transcription).

Overall, what are the benefits of RNA splicing?

They provide eukaryotes with the ability to produce a variety of proteins from a single gene, and it allows them to evolve new genes by mixing-and-matching exons from preexisting genes.

When does this capping occur?

This capping occurs after RNA polymerase II has produced about 25 nucleotides of RNA, long before it has completed transcribing the whole gene.

ESSENTIAL CONCEPT #4 FROM BOOK

To begin transcription, RNA polymerase binds to specific DNA sites, called promoters, that lie immediately upstream of genes. To initiate transcription, eukaryotic RNA polymerases require the assembly of a complex of general transcription factors at the promoter, whereas bacterial RNA polymerase requires only an additional subunit, called a sigma factor.

ESSENTIAL CONCEPT #1 FROM BOOK

To express the genetic information carried in DNA, the nucleotide sequence of a gene is first transcribed into RNA. Transcription is catalyzed by the enzyme RNA polymerase, which uses nucleotide sequences in the DNA molecule to determine which strand to use as a template, and where to start and stop transcribing.

QUIZ Q #4 Which of these RNAs translates RNA into protein?

Transfer RNA (tRNA)

ESSENTIAL CONCEPT #8 FROM BOOK

Translation of the nucleotide sequence of an mRNA into a protein takes place in the cytoplasm on large ribonucleoprotein assemblies called ribosomes. As the mRNA moves through the ribosome, its message is translated into protein.

what are the three stop codons?

UAA, UAG, UGA -these stop codons are not recognized by a tRNA and do not specify an amino acid

QUIZ Q #9 What amino acids are deposited on a growing polypeptide chain when the stop codons arrive?.

a) none b) phe c) met d) tyr ANSWER: none

What type of genes are transcribed in RNA polymerase II?

all protein-coding genes, miRNA genes, plus genes for other noncoding RNAs (e.g those in spliceosomes)

ribozymes

catalytic RNA molecules that function as enzymes and can splice RNA

post-translational modification

changes to the new protein after it has left the ribosome, that may be critical to its being a useful function in the cell examples: >covalent modification (phosphorylation) >the binding of small-molecule cofactors >association with other protein subunits

messenger RNAs (mrnas) function?

code for proteins

What do aminoacyl-tRNA synthetases do?

covalently connect each amino acids to its appropriate set of tRNA molecules; also the enzymes that charge tRNA to be able to carry out its role as an adaptor. *each synthetase enzyme recognizes specific nucleotides in both the anticodon and the amino acid-accepting arm of the correct tRNA

ribosomal RNAs (rrnas) function?

form the core of the ribosome's structure and catalyze protein synthesis

In the process of translating a nucleotide sequence into an amino acid sequence, the sequence of nucleotides in an mrna molecule is read how?

from the 5′ to the 3′ end in sequential sets of three nucleotides

QUIZ Q #7 What is the eukaryotic equivalent to the bacterial sigma factor?

general transcription factors

What is a codon?

group of 3 consecutive nucleotides in RNA, and each codon specifies one amino acid.

anticodon

group of three bases on a tRNA molecule that are complementary to an mRNA codon that bind through base pairing;anticodon codes for the aminoacids

What does the two capping and polyadenylation modifications do for the mRNA molecule?

increase the stability of a eukaryotic mRNA molecule, helps with the export from the nucleus to the cytoplasm, and generally mark the RNA molecule as a mature mRNA.

What type of genes are transcribed in RNA polymerase III?

tRNA genes, 5S rRNA gene, genes for many other small RNAs

what does this initiator tRNA do?

it always carries the amino acid methionine (MET) (newly made proteins all have methionine as the first amino acid at their N-terminal end, the end of a protein that is synthesized first

what does this reaction do?

it frees the carboxyl end of the polypeptide chain from its attachment to a tRNA molcule; because this is the only attatchment that holds the growing polypeptide to the ribosome, the completed protein chain is immediately released. at this point, the ribosome also releases the mRNA and dissociates into its two separate subunits, which can then assemble on another mRNA molcule to begin a new round of protein synthesis.

QUIZ Q #15 Why is DNA currently the dominant genetic storage medium?

it is more stable than RNA

What must happen before a EUKARYOTIC mRNA can be translated into protein?

it must be transported out of the nucleus through small pores in the nuclear envelope

What type of genes are transcribed in RNA polymerase I?

most rRNA genes

QUIZ Q #12 The ribosome....

moves to shift transcripts

QUIZ Q #13 If you wanted to prevent a specific protein from being degraded by the proteosome, you might...

mutate the site where it is ubiquitlated

QUIZ Q #8 Which of these is not an element of pre-mRNA processing to produce the final mRNA?

nuclear transport receptor

The two RNA processing steps, capping and polydenylation, occur only on what?

occur only on RNA transcripts destined to become mRNA molecules (called precursor mRNAs or pre-mRNAs)

what does polycistronic mean?

one mRNA molecule encodes MANY different proteins

what do release factors do?

proteins that bind to any stop codon that reaches the A site on the ribosome; this binding alters the activity of the peptidyl transferase in the ribosome, causing it to catalyzze the addition of a water molecule instead of an amino acid to the peptidyl-tRNA

What is gene expression?

refers to the process by which the information encoded in a DNA sequence is translated into a product that has some effect on a cell or organism.

microRNAs (mirnas) function?

regulate gene expression

The efficient synthesis of polynucleotides by complementary mechanisms require what?

requires catalysts to promote the polymerization reaction: without catalysts, polymer formation is slow, error-prone, and inefficient.

transfer RNAs (trna's) function?

serve as adaptors between mRNA and amino acids during protein synthesis

stop codons

signal the end of an amino acid chain and signal the ribosome to stop translation

RNA splicing is carried out largely by what....

small nuclear RNAs (snRNAs) that are packaged with snRNPs.

what do snRNPs form?

snRNPs form the core of the SPLICEOSOME, the large assembly of RNA and protein molecules that carries out RNA splicing in the nucleus.

ESSENTIAL CONCEPT #11 FROM BOOK

tRNAs act as adaptor molecules in protein synthesis. Enzymes called aminoacyl-tRNAs synthestases covalently link amino acids to their appropriate tRNAs. Each tRNA contains a sequence of three nucleotides, the anticodon, which recognizes a codon in an mRNA through complementary base-pairing.

what does the 5' cap do?

tells the ribosome where to begin searching for the start of translation

the origin of life requires molecules to possess what crucial property

the ability to catalyze reactions that lead, directly or indirectly, to the production of more molecules like themselves.

The translation of an mRNA begins with what?

the codon AUG and a charged tRNA is required to initiate translation

what allows each codon in the mRNA molecule to specifiy its proper amino acid?

the combined action of the synthetases and tRNAs that allows each codon in the mRNA molecule to specify its proper amino acid

What do proteases do?

the enzymes that degrade proteins, first to short peptides then to individul amino acids; they act by cutting/hydrolyzing the peptide bonds between amino acids of proteins

RNA capping

the modification of the 5' end (end that is synthesized first) by capping the RNA with an atypical nucleotide (a guanine (G) nucleotide bearing a methyl group, attached to the 5′ end of the RNA).

Proteolysis refers to what?

the specialized pathway that cells take to enzymatically break proteins down into their constituent amino acids

what happens when the synthesis of the protein is finished?

the two subunits of the ribosome separate

What was the reason that enabled RNA molecules to have a central role in the origin of life?

the unique potential of RNA molecules to act both as information carriers and as catalysts

what is the function of snRNPs (small nuclear ribonucleoprotiens)

they recognize splice-site sequences through complementary base-pairing between their RNA components and the sequences in pre-mRNA, and they direct the cleavage of the RNA at the intron-exon borders and catalyze the covalent linkage of the exon sequences.

What do transfer RNA molecules (tRNAs) do during protein synthesis?

they're adaptor molecules that can recognize and bind to a codon at one site on their surface and to an amino acid at another site; consist of a set of small RNA molecules about 80 nucleotides in length. *there is more than one tRNA for many of the amino acids *some tRNA molcules can base-pair with more than one codon (tRNA is an adaptor between mRNA and amino acids during protein synthesis and combines the both of them to make a polypeptide chain to be made into a protein)

What is the main role of the ribosomal proteins?

to help fold and stabilize the RNA core

alternative splicing

transcripts of many eukaryotic genes that can be spliced in many different ways, leading to different mRNAs that code for different proteins, increases the diversity of protein and the coding potential of their genomes. (95 percent of human genes undergo alternative splicing) random exons are being chosen to be spliced/aka exons can be skipped over by the splicesome to produce alternatively spliced mRNA but the DNA sequence cannot be rearranged.

Polyadenylation

trimming of the 3' end by an enzyme that cuts the RNA chain, then its the addition of multiple adenine nucleotides to the 3' end (end of the chain synthesized by the RNA polymerase) of a newly synthesized mRNA molecule

What is crucial to the function of tRNAs in protein synthesis?

two regions of unpaired nucleotides situated at either end of the L-shaped tRNA molecule

How does the cell determine which parts of the RNA transcript to remove during splicing?

unlike the coding sequence of an exon. most of the nucleotide sequence of an intron is not important; each intron contains a few short tagnucleotide sequences that act as cues for its removal from the pre-mRNA, sequences found near each end of the intron. guided by these sequences, a splicing machine cuts out the intron in the form of a lariat structure as discussed in the notecard above.

other noncoding RNAS function?

used in RNA splicing, gene regulation, telomere maintence, and many other processes

QUIZ Q #11 Translation....

uses tRNAs possessing an anti-codon