Chapter 14- Gene Expression

Alteration of mRNA ends in Eukaryotes Each end of a pre-mRNA molecule is modified in a particular way =The 5' end receives a modified G nucleotide ___ The 3' end gets a ________ These modifications share several functions Facilitating the ___ of m R N A to the cytoplasm Protecting m R N A from _____ _____ Helping ribosomes attach to the ___end

5' cap poly-A tail export hydrolytic enzymes 5'

Figure 14.8: The Stages of Transcription _____- After RNA polymerase binds to the promoter, the DNA strands unwind, and the polymerase initiates RNA synthesis at the start point on the template strand _______ The polymerase moves downstream, unwinding DNA and elongating in the RNA transcript 5' to 3'. In the wake of transcription, the DNA strands re-form a double helix ______- eventually , the RNA transcript is released, and the polymerase detaches from the DNA

Initiation Elongation Termination

Figure 14.12 RNA Processing: RNA splicing ______-are highly variable in size 50 - 100,000 nucleotides in length Drosophila avg = ~70,000 nucleotides DMD Duchene muscular dystrophy = 2.5 million bp w/ 78 introns Intron size and genome size are positively correlated Not essential, but some sequences w/in introns regulate gene expression • _____ occur more rapidly in introns

Introns Mutations

Genotype -> ______ "Black Urine" disease Lack ____- to break down alkapton Builds up in joints (osteoarthritis), heart valves, and kidney stones Excess excreted in urine -> turns black upon exposure to air

Phenotype enzyme

in _________-translation of m R N A can begin before transcription has finished

bacteria

During translation, the m R N A base triplets, called _____-, are read in the 5' to 3 direction Each codon specifies the amino acid (one of 20) to be placed at the corresponding position along a polypeptide The term codon is also used for the D N A nucleotide triplets along the nontemplate strand The nontemplate D N A strand is also called the ____ ______ Start codon is always ____ (mRNA) in 5 to 3' direction

codons coding strand AUG

The Genetic Code There are only four nucleotides bases to specify 20 amino acids How do the four DNA bases encode the sequence of proteins that contain 20 different amino acids? Different ______- vs using each nucleotide to encode for one amino acid(3 base code) How many nucleotides correspond to an amino acid? ___

combinations 3

Prokaryotic transcription _____ to translation- no need to move anything out of a nucleus Ecoli can carry out so quickly for example Since there are no _____ these processes can(and do) occur simultaneously or concurrently

coupled organelles

Concept 14.3: Eukaryotic Cells Modify RNA after Transcription Enzymes in the Eukaryotic nucleus modify pre-mRNA (RNA processing) before the genetic messages are dispatched to the _____- During RNA processing, both____of the primary transcript are altered Also, usually some _____ parts of the molecule are cut out and the other parts spliced together

cytoplasm ends interior

Figure 14.9: The Initiation of Transcription at a Eukaryotic Promotor 1.) A eukaryotic ______-- commonly includes a TATA box (a nucleotide sequence containing TATA) about 25 nucleotides upstream from the transcriptional start point 2.) _____ _____ _____-- one recognizing the TATA box, must bind to the DNA before RNA polymerase II can bind in the correct position and orientation 3.) additional transcription factors (purple) bind to the DNA along with RNA polymerase II forming the transcription initiation complex. RNA polymerase II then _____- the DNA double helix and RNA synthesis begins at the start point on the template strand

promoter Several Transcription factors unwinds

RNA synthesis utilizes only one DNA strand of a gene as a template Template is in ___ to ___ prime and RNA strand is gonna be in ___ to ___ (complement to template)- identical to ______ strand(U's instead of T's)

3' to 5' 5' to 3' nontemplate

CRACKING THE CODE All 64 codons were deciphered by the mid-1960s Of the 64 triplets, 61 code for amino acids; 3 triplets are "stop" signals to end translation ____ is both a "start" codon and codes for Met The genetic code is ______: more than one codon may specify a particular amino acid But it is not ambiguous: no codon specifies more than one amino acid

AUG redundant ambiguous

The______ ______ is the concept that cells are governed by a cellular chain of command Occurs in every ____ ____ DNA->RNA-> Protein Crick's "Central Dogma" hypothesis Transcribe an RNA copy from DNA instructions RNA-> Direct functional role RNA ->instructions for protein Translate mRNA into protein Proteins-> Polymers made up of ____ ____-monomers One things got to their final product, they never go back

Central Dogma living cell amino acid

_____: Triplets of Nucleotide The flow of information from gene to protein is based on a triplet code: a series of nonoverlapping, three-nucleotide words The words of a gene are transcribed into ________nonoverlapping three-nucleotide words of m R N A

Codons complementary

Bacterial Promoters Two short conserved sequences referred to by their midpoints relative to transcription initiation site -10 nontemplate strand consensus TATAAT -facilitates ____ _____ Only two hydrogen bonds since two nucleotides -35 nontemplate strand consensus TTGACA - ______ ____recognized by RNA polymerase

DNA unwinding binding site

Evidence from the Study of Metabolic Defects In 1902, British physician Archibald ____- first suggested that genes dictate phenotypes through _____ that catalyze specific chemical reactions He thought symptoms of an inherited disease reflect an inability to synthesize a certain enzyme In 1902, Garrod describe the inherited disorder alkaptonuria as an "inborn error of metabolism". He proposed that a _____ ______ was causing a specific defect in the pathway for eliminating liquid wastes. Cells synthesize and degrade molecules in a series of steps, a _____ _____

Garrod enzymes gene mutation metabolic pathway

Molecular components of Transcription An enzyme called _____ ______-pries the D N A strands apart and joins together the complementary R N A nucleotides(transcription bubble) =Complementary to DNA template strand =Identical to DNA nontemplate strand EXCEPT Thymines replaced with ____- R N A polymerases assemble polynucleotides only in the ___ to ____direction Unlike D N A polymerases, R N A polymerases can start a chain without a primer (__ ____ synthesis)

R N A polymerase Uracil 5' to 3' de novo

Eukaryotic R N A transcripts are modified through ______ _____-to yield the finished m R N A

RNA processing

Is the relative instability of RNA a good thing???- DNA as the hereditary genetic material, it is important to be stable. RNA varies from cell to cell and changes often, it has to be ____- We only want to express RNA when it is appropriate time.

dynamic.

in ________, the nuclear envelope separates transcription from translation

eukaryotes

Concept 14.2: Transcription is the D N A-Directed Synthesis of R N A: A Closer Look Transcription is the _____stage of gene expression Transfer of genetic information from DNA to RNA Synthesis of RNA is similar to DNA synthesis except: Ribonucleoside Triphosphates are monomers Only one strand of DNA is ____- for RNA No ___- required, de novo synthesis RNA is ____-, short-lived compared to DNA

first template primer unstable

Transcription produces _______

messenger R N A (m R N A)

Figure 14.13 A Spliceosome Splicing a pre-mRNA Highly ____ removal of each intron Must be precise, one base addition/deletion will make a huge difference Signal Sequence for splicing: dinucleotide at each end of the intron 5'-Exon-[GT---INTRON---AG]-Exon-3' on Non-Template Strand

price

The Products of Gene Expression: A developing story Some proteins are _____ ____-, so researchers revised the one gene-one enzyme hypothesis to: one gene-one protein Many proteins are composed of several _____, each of which has its own gene Therefore, Beadle and Tatum's hypothesis is now restated as the one gene-one_____hypothesis It is common to refer to gene products as proteins rather than polypeptides

not enzymes polypeptides polypeptide

Eukaryotic m R N A must be transported out of the ______to be translated A primary transcript is the initial R N A transcript from any gene prior to processing RNA Processing 5' 7-MG cap 3' Poly-A tail Removal of ____- Translation in the ______

nucleus introns cytoplasm

Codons must be read in the correct reading frame (correct groupings) in order for the specified polypeptide to be produced Codons are read ___ at a time so nonoverlapping Evolution of Genetic Code The genetic code is nearly _____, shared by the simplest bacteria and the most complex plants and animals Genes can be transcribed and translated after being _____- from one species to another A language shared by all living things must have been operating in the ____ ______ of all present-day organisms

one universal transplanted common ancestor

These words are then translated into a chain of amino acids, forming a ______- During transcription, one of the two D N A strands, called the template strand, provides a template for ordering the sequence of complementary nucleotides in an R N A transcript The ______strand is always the same strand for any given gene However, elsewhere on the chromosome, the opposite strand may function as the template for a different gene

polypeptide template

Overview: The Flow of Genetic Information The information content of genes is in the form of specific sequences of nucleotides in D N A The D N A inherited by an organism leads to specific traits by dictating the synthesis of proteins and of R N A molecules involved in ____ ____ Proteins are the link between ____- and phenotype _______-, the process by which D N A directs protein synthesis, includes two stages:______ and ______

protein synthesis genotype Gene expression Transcription Translation

In some organisms, R N A splicing can occur without _____, or even additional R N A molecules The introns can catalyze their own _____ The discovery of ribozymes invalidated the idea that all biological catalysts are proteins

proteins splicing

Nutritional Mutants: Scientific Inquiry In 1941, Beadle and Tatum began studying the haploid bread mold Neurospora crassa because it would be easier to detect ____ _____- They studied mutations that altered the ability of the fungus to ____ on minimal medium They generated nutritional mutants, each of which was unable to synthesize a particular essential nutrient The researchers amassed a valuable collection of Neurospora mutant strains, catalogued by their defects For example, one set of mutants all required _____for growth It was determined that different classes of these mutants were blocked at a different step in the biochemical pathway for arginine biosynthesis One gene-_____ ____- hypothesis

recessive mutations grow arginine one enzyme

Split Genes and R N A Splicing in Eukaryotes (1 of 2) In R N A splicing, large portions of the R N A molecule are removed and the remaining portions ______- The noncoding regions are called intervening sequences, or _____- -1977 found eukaryotic genes contain noncoding intron The other regions are called _____and are usually translated into amino acid sequences In the process of splicing, the introns are cut out from the molecule and the exons ____ together Many genes can give rise to two or more different ______, depending on which segments are used as exons This process is called _______ ____ ____ Rearrangement of exons give ____ ____- R N A splicing is carried out by ______ -consist of proteins and small R N A's

reconnected introns exons joined polypeptides alternative R N A splicing new combinations spliceosomes

are R N A molecules that function as enzymes

riboenzymes

Basic Principles of Transcription and Translation (1 of 5) R N A is the bridge between D N A and protein synthesis R N A is chemically similar to D N A, but R N A has a _____sugar instead of deoxyribose and the base _____(U) rather than thymine (T) R N A is usually_____ ____- Ribose sugar has ______ group attached

ribose uracil single-stranded hydroxyl

are the sites of translation (protein synthesis)

ribosomes

Tobacco plant expressing a firefly gene The yellow glow is produced by a chemical reaction catalyzed by the protein product of the firefly gene Mosquito larva expressing a jellyfly gene Researchers hope to use a _____ _____to insert a gene that will make mosquitoes unable to transmit malaria Viruses use host living cell to replicate

similar technique

repeating mRNAs direct synthesis of polypeptide with two different amino acids

synthetic dinucleotide

repeating mRNAs direct synthesis of three different polypeptides each containing the same amino acid

synthetic trinucleotide

Termination of Transcription The mechanisms of termination are different in bacteria and eukaryotes In Bacteria, the polymerase stops transcription at the end of the_____ and the m R N A can be translated without further modification In Eukaryotes, R N A pol II transcribes the _______ signal sequence; the R N A transcript is released 10-35 nucleotides past this polyadenylation sequence AAUAAA

terminator polyadenylation

is the synthesis of R N A using information in D N A

transcription

is the synthesis of a polypeptide, using information in the m R N A

translaton

Elongation of the R N A Strand As R N A polymerase moves along the D N A, it ______ the double helix, 10 to 20 bases at a time Transcription progresses at a rate of ___nucleotides per second in eukaryotes A gene can be transcribed______ by several R N A polymerases

untwits 40 simultaneously

RNA Polymerase Binding and Initiation of Transcription in Prokaryotes (1 of 2) Promoters signal the transcriptional start point and are ______ of the start point contain the initiation sequences for RNA polymerases

upstream

RNA Polymerase Binding and Initiation of Transcription in Eukaryotes (1 of 2) Promoters that signal the transcriptional start point in Eukaryotes are usually several dozen nucleotide pairs _____-of the start point A promoter D N A sequence called a_____box is crucial in forming the initiation complex in eukaryotes Transcription ____ mediate the binding of R N A polymerase and the initiation of transcription The completed assembly of transcription factors and R N A polymerase II bound to a promoter is called a _____ _____ ____-

upstream TATA factors transcription initiation complex