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135 Cards in this Set
- Front
- Back
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Describe the bond that joins nucleotides in DNA
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nucleotides are joined at the 3' and 5' carbons through a phosphodiester bridge. The oxygen from the 3' carbon of the 5' end of the strand attacts the phosphate group of the 5' carbon on the new 3' end.
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Describe the significant of major and minor groves in the B DNA right handed helix
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The grooves are lined with potential hydrogen bond donor and acceptor atoms where DNA binding proteins can interact. Many DNA binding proteins bind in the major groove of DNA in a sequence specific manner. Drugs with flat planar rings can interact with the minor groove of DNA
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List 3 factors that help stabilize the DNA double helix
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1. Hydrogen bonding between base pairs (A+T, G+C, or A+U in RNA)
2. Resonance stabilization resulting from stacking of aromatic rings 3. ionic interatcions |
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List two factors that can denature DNA.
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1. pH
2. heat Note that the ionic composition of the solution will effect denaturation and annealing rates |
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Describe the hyperchromic shift associated with DNA
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when DNA is annealed, it aborbs less light at 260nm because the stacked form's electrons are "busy" interacting with the other bases and less able to absorb light. The absorbance curve is shorter.
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List two factors that can alter the Tm of DNA
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1. GC content- GC pairs have 3 hydrogen bonds compared to AT pairs that have 2. More hydrogen bonds leads to a more stable structure and thus a higher melting point (more GC, higher Tm)
2. Ionic strength of the solution- high salt favors the duplex, low salt favors denature. Electrostatic repulsion occurs as a result of the charged backbone so it is more favorable for the helix to be together in a salty soulution (high salt= high Tm) |
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Describe two key differences between topoisomerases I and II
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1. Energy. Topo I is ATP independent, Topo II is dependent
2. Type of break- Topo I is single stranded break and removes 1 loop of supercoiling, Topo II makes a double stranded break and removes 2 loops of coiling. |
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List in order from smallest to largest the hierarchy of chromatin structure
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1. nucelosome
2. 30nm fiber 3. Chromatin Loop 4. miniband 5. chromosome remember: "Never Forget Lust Makes Children" |
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What is the difference between euchromatin and heterochromatin?
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euchromatin is loose and actively being transcribed, heterochromatin is concentrated at the nuclear margins and is less actively transcribed
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Describe each component of the histone octomer
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two histone dimers H2A and H2B combine with one histone tetramer 2 x H3/H4 to form the octomer
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What is the role of the H1 histone protein
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H1 is the linker protein that is located between octomer beads, it is involved in 30nm fiber packaging
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What is the overall charge on histone proteins and why is this significant
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Histone proteins are basic due to the enrichment of lysine and arginine residues. This positive charge helps them attract to the negativley charged, acidic DNA
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What is the general function of histone proteins in addtion to packaging the genome
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Inhibit transcription
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There are 3 types of histone modifications. Breify describe each one in terms of purpose and mechanism.
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1.Acetylation. When histones are acetylated, they lose their basic charge and no longer adhere to DNA. This opens the chromatin structure and makes way for transcription.
2.Methylation. Methylation of H3 creates a binding site for HP1 which leads to the formation of non-transcribable heterochromatin 3. Phosphorylation- assocaited with the repression of transcription that occurs during condensation of chromatin |
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How does histone methylation lead to the repression of gene expression
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The histone protein H3 is methylated which creates a binding site for HP1. When HP1 is bound the DNA becomes non-transcribable (heterochromatin)
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What two modifications occur to nucelosomes during gene activation
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1. dissolution of one or two nucelosomesfrom the gene promoter and H1 from linker DNA
2.Histone Acetylation by histone acetyl transferases (which also transcription factors) |
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Describe the structure of the nucelosome
How many base pairs of DNA does this compact? |
-core of 8 histone proteins
-two loops of 70bp looped around each octomer -60 bp between each octomer -200bp/ nucelosome |
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Describe the structure of the 30nm fiber
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-6 nucelosomes around one turn of a solenoid
- packaged using H1 |
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Describe the structure of the chromatin loop
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-3rd order
-~50 fibers coiled into a loop for about 60,000 bp |
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What is the significance of the spacial relationship between chromatin loops and the nuclear matrix?
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The bases of each loop contain the active areas of the genes are attached to the matrix. The matrix houses important structural and gene regulatory information. The looping also allows the coiled DNA to interact with distant regulatory regions.
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Describe the structure of minibands
What order of chromatin structure are they? How many base pairs do they condense |
-4th order structure
-18 loops so about 1 million bp -tandem loops that encircle the chromosome axis |
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Describe the structure of mitotic chromosomes
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-5th order of chromatin structure
-75 minibans so 75 million bp -characterized by centromere and telomere |
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What event must happend to chromatin proteins in order for the mitotic chromosome to form?
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hyperphosphorylation especially of H1
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Why is a primer needed in DNA replication
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there must be a free 3' OH group to attack the phospate on an incoming dNTP
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Describe the 3 catalytic activities of DNA polymerase
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1. 5'=>3' polymerase- adds the nucelotides
2. 5'=>3' exonuclease- removes RNA primers 3. 3'=>5' exonuclease-proofreading, removes incorrect base pairs |
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How do proks and euks differ in terms of origins of DNA replication
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proks have one origin, euks have many
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How do DNA pol I and III differ in terms of
processivity exonuclease activity |
DNA pol III is very processive, DNA pol I is not
DNA pol III lacks 5-3 exonuclease activity |
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Why is telomerase needed
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Primer dependence and 5' to 3' directionality of DNA pol results in incomplete lagging strand
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Describe the ends of the eukaryotic chromosomes
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The ends aka telomers consist of many tandem repeats of the sequence GGGGTT (6). The repeates are synthe sized by telmerase a reverse transcriptase (RNA dependent DNA polymerase) that carries its own RNA template
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What are the two subunits of telomerase
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TERT-reverse transcriptase protein
TERC- RNA component (template) |
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Describe in detail how the lagging strand is formed
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1. Primase creates an RNA primer
2. DNA pol III elongates the primer to form an Okazaki fragment 3. DNA poI I also extends the fragment and removes the RNA primer (5'-3' exonuclease) 4. DNA ligase seals the gap |
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Which DNA polymerase is mainly responsible for synthesizing the leading strand
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DNA pol III (more processive but no exonuclease activity
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In which direction does polymerase proofreading occur
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3' to 5'
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What are the phases of the cell cycle? Breifly describe what occurs in each stage
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G1- senscence (G0), differentiation (G0) apoptosis, proliferation
S- DNA synthesis G2- Prep for mitosis, centrosome duplicated, hyperphosphorylation of histone proteins M- mitosis |
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WHich phase of the cell cycle deterimines the generation time Tg of the cell
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G1
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Describe the external factors or primary messengers that regulate the cell cycle
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Secreted molecuels and peptides like growth factors, cytokines, and hormones which interact with a receptor. These factors can initiate or inhibit the cell cycle
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Describe the internal factors or secondary messengers that regulate the cell cycle
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The early responses genes such as myc, fos, and jun which respond to growth signals. Second messengers also include delayed response genes which include cdks and cyclins
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Describe the structure and role of cyclin dependent kinases
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Heterodimeric secondary messengers of the cell cycle.
CDK= catalytic protein that phosphorylates the target, levels remain constant Cyclin subunit- regulatory, levels increase and decrease |
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What is the role of p27 is the cell cycle
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p27 inhibits the cell cycle. its level decreases as the cell progresses through G1
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What heterodimer is required to activate G1
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cyclinD/CDK4.
note cyclin D gene is activated by the cmyc gene which can be turned on by Wnt growth factors wia Bcatenin. Can also be activated by the ras, MAP kinase pathway |
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WHat happens to the levels of cyclin D throughout the cell cycle
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remain increased
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Imagine that a Wnt growth factor binds a cell and increases B catenin which migrates to the nucleus and activates transcripton of the c-myc gene which activates the cyclin D gene. What does cyclin D do next to turn on the cell cycle?
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1. Cyclin D binds CDK4 to form cyclinD/CDK4 heterodimer
2. the heterodimer phosphorylates Rb forming 3. Phosphorylated Rb releases its hold on E2F 4.E2F can go on to activate genes for cyclins E and A |
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What must occur in order for the genes for cyclins E and A to be acticated
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cyclinD/CDK4 must phosphorylate Rb so that Rb releases E2F which is the transcription factor for the genes for cyclins E and A
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What heterodimer(s) is/are needed to activate S phase
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CyclinE/CDK2 and CyclinA/CDK2
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What is the role of cyclinE/CDK2 in the cell cycle
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cyclin E is upreguated in response to E2F which is released from Rb when Rb is phosphorylated by CyclinD/CDK4. CyclinE/CDK2 allows for the breech of the restricition point. Once past the restriction point, the cell is commited to complete the cell cycle, ensuring that the whole genome is replciated in S phase
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What is the role of cyclinA/CDK2 in the cell cycle
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CyclinA is upregulated in response to E2F, a transciption factor that is release from Rb when Rb is phosphorylated by CyclinD/CDK4. CyclilnA/CDK2 activates poised DNA replication complexes at the multiple origins of DNA replication. The cyclinA dependent phosphorylation prevents the formation of new DNA replication complexes ensuring that the genome is replicated only once.
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How do CyclinE and Cyclin A + CDK2 work together to ensure that the genome is properly copied
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Cyclin E breeches the restriciton point and ensures that the cell is ready to replicate the whole genome
Cyclin A phosphorylates the poised replicaiton complexes to ensure that the genome is replicated only once |
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Explain how M phase is activated
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M phase is activated at the G2/M boundry when cyclinB/CDK1 is DEphosphorylated (DE!!!!) by cdc25. Dephosphorylated cyclinB/CDK1 enters the nuclues and phosphorylated target proteins leading to nuclear envelope breakdown, mitotic spindle assembly and metaphase arrest.
Rember (you have to be naked to get to the nuclues) |
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what is the role of cdc25 in the cell cycle
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cdc25 is a phosphatase that de-phosphorylates CyclinB/CDK1 so that the heterodimer can get into the nucleus and phosphorylate target proteins
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What are the downstream affects of cdc25 mediated dephosphorylation of CyclinB/CDK1
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The dimer enters the nuclues and cuases
-nuclear envelope breakdown -mitotic spindle assembly -metaphase arrest |
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tumor supressor genes
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genes which encode inibitory supressor proteions that inhibit the cell cycle
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Expalin how Rb acts as a tumor supressor gene
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Rb binds E2F and prevents E2F from transcribing the genes for Cyclins E and A
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How does p21 act as a tumor supressor gene
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p21 inhibits CDK2 and CDK4. Without CDK2, cyclins E and A cannot function and the cell cannot proceed through S phase. WIthout CDK4, cyclinD cannot function and the Rb cannot be phosphorylated thus E2F cannot be released
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How does p27 act as a tumor supressor
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similar to p21, inhibits CDK2 and 4
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What are the two ways that p53 inhibits the cell cycle
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1. induces the transcription of p21 which inhbits CDKs 2 and 4
2. Promotes apoptosis |
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Describe what is occuring during the prophase stage of Mitosis
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-chromatin condenses and sister chromatids pair up (AA, aa the DNA has already been duplicated in S phase)
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Describe what is occuring during prometaphase of Mitosis
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-Nuclear envelop breakdown
-kinetochores envelop each centromere -microtubules appear (astral, kinetochore, and polar) |
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Describe what is occuring during the metaphase of mitosis
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-chromosomes align on metaphase plate
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Describe what is occuring during the anaphase stage of mitosis
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The anaphase promoting complex (ubiquiting ligase) marks cohesion proteins for degradation allowing the sister chromatids to be separated via shortening kinetochore microtubuels (pull) and lengthening polar microtubles (push)
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Describe what is happening during the telophase stage of mitosis
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nucleus reforms ocmpleting karyokinesis
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Describe what is happening during that cytokinesis stage of mitosis
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cytoplasm divides at clevage furrow compelting cytoplasmic division (note nuclear and cytoplasmic are two different steps, telophase and cytokinesis respectivley)
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how do mitosis and meiosis differ in terms of number of divisions?
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mitosis-one cell division resulting in two daughter cells
meiosis- two cell divisions resulting in four products of meiosis |
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How do mitosis and meiosis differ in terms of chromosome number per nucleus maintained
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mitosis-2N to 2X 2N
meiosis- 2N to 4x N |
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How do mitosis and meiosis differ in terms of paring of homologs
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mitosis-no pairing
meiosis- full synapsis at prophase I |
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T/F crossing over occurs in mitosis
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false. crossing over only occurs in meiosis. Crossing over requires that homologous chromosomes be adjacent which does not occur in mitosis
Additionally, the purpose of mitosis is to produce daughter cells that are exactly identical to the parent genotype. Crossing over would mess this up. |
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How does the division of centromeres differ in mitosis and meiosis
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In mitosis, the chromatids are pulled apart at the centromeres during anaphase. This allows one chromatid of each pair to be given to the daughter cell ensuring that all 46 chromatids wind up in the daughter. In meiosis, the centromeres do not divide at anaphase 1 allowing but they do at anaphase 2. This ensures that each product has 23 unique chromatids in it
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when does crossing over occur
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prometaphase I of meiosis
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In meiosis the _____separate in anaphase I and the ____ separate in ana phase II
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In meiosis the homologous chromosomes separate in anaphase I and the sister chromatids separate in anaphase II
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Explain how the meiotic division 1 is a reductive division leaving a DNA content of 2N but 23 chromosomes
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after the first mitotic division, the homologous chromosomes have seaparated leaving 2 daughter cells with 23 chromosomes. There are 46 chromatids because each gene was copied in the begining but the centromeres have not separated. The 46 unseparated chromatids make up 23 chromosomes
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Describe how chromosomes present in diploid somatic cells
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The chromosomes are present in homologous paris with each chromosomes containing one allele from mom and one from dad
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What does the law of equal segregation (mendel's 1st law) say
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Each gamete receives only one allele of each gene. The gamete receives the maternal or paternal allele for a particular gene but not both.
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When does independent assortment occur
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Meiotic division 1
The homologous chromosomes have aligned on the metaphase plate but maternal and paternal do not have to be on opposite sides. Each pair segregates indepedently |
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What ratio of pheontypes is generated from a dihybrid cross of heterozygotic parents
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9:3:3:1
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what is a recombinant gamete
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A gamete whose gentotype is unique from either parent, results from independent assortment
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Describe linkage maps and centimorgans
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A linakge map diptics the order of genes based on crossing over frequencies. Genes that have a low frequency of crossing over are tightly linked and must be close together. Genes that have a high frequency of crossing over are loosley linked and farther apart. A 1% frequency of crossing over is equivalent to 1 centiMorgan which is about 1 million bp in humans. The farthest apart you can be is 50cM indicating a 50% chance of crossing over which is the rate for completely unlinked genes
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list 4 ways DNA can mutate
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1. mis incorporation of nucleotides during replicaiton
2. inherent chemical instability of based 3. environmental mutagens 4. inonizing radiation |
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what is the difference between a transition and transversion mutation
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transition-purine to purine, or pyrimidine to pyrimidine
transversion- purine to pyrimidine or vice versa (transvestites put on extra clothes=> gain or lose a ring) |
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explain how mismatch repair works
What proteins are needed? |
-methylation marks original strand
-Mut proteins recognize mismatch and nick strand -DNA helicase unwinds, exonuclease II degrades -Pol III and ligase patch |
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explain how base excision repair works to fix damaged bases
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-DNA glycosylase removes the damaged base leaving backbone in tact
-ap endonuclease opens the backbone -Pol I adds a new base -ligase reseals backbone |
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explain how nucleotide excision repair works to fix large structural damage
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XP or ERCC genes encode the tools
-excinuclease and helicase remove large chunk of DNA strand -polymerase and ligase redo it |
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explain how direct repair works
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Enzymatic reversal of damage to DNA. For example, the MGMT (AGT) enzyme can remove alkyl groups from guanine residues (o6methyl guanine)
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Expalin the role of MGMT in chemo therapy
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an alkylating agent can be given to damage the DNA of rapidly growing cells. A MGMT inhibitor is then also given so that the alkyl group is not removed from the DNA bases as it would normally be by the direct repair system
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explain how recombinational repair works
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-fixes leisions when there is no complimentary strand available e.g. double stranded breaks, double stranded cross links, and leisions in single stranded regions
-information to preform the repair comes from the homologous chromosome |
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t/F a primer is required for transcription
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false, rna polymerase does not need a primer
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what is the purpose of the sigma factor in prokaryotic RNA polymerase
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it gives specificity and allows the holoenzyme to recognize the promoter regions on the DNA, allows for regulation of gene expresision
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T/F prokaryotic RNA polymerase has proofreading activity
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false but this is ok because the information is not stably inherited. a mistake here is not as costly as a mistake in DNA synthesis
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What three components make up an operon
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1. promoter-site for binding RNA polymerase
2. Operator- binding site for represser of activator 3. structural gene |
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Describe the two important regions of a prokaryotic promoter
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-35=site of initial protein-DNA complex, "closed complex"
-10= beginning of unwinding and formation of the "open complex" |
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describe prokaryotic protein dependent termination of transcription
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-active signals for termination lie in the newly formed RNA chain
-the transcript forms a hairpin loop which causes the polymerase to pause -The rho protein binds to the ssRNA and moves towards the transcription complex -When rho catches polymerase it breaks the DNA-RNA hybrid and transcription terminates |
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Describe prokaryotic protein independent termination of transcription
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-hairpin loop with run of adenylates in the template strand leading to run of U's in transcript
-loop causes poylmerase to pause -A-U hybrid is unstable and complex falls apart |
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What is the significance of the separation of eukaryotic transcription and translation by space and time
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allows for extra regulation because the RNA is free for a while, examples include modification of 1/2 life and splicing
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List 3 major post-transcriptional modifications of eukayotic mRNA
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1. 5' cap
2. poly A tail 3. splicing |
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what is the purpose of the 5' cap
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enhanced stability and increased translational efficeincy
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Describe how the 5' cap is formed (what unique linkage is made?)
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7 methyl guanosine is added to the 5' end of the primary transcript by guanylyltranserase creating a 5' to 5' triphosphate pridge between the 7mG andthe 5' most sugar in the transcript
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What is the purpose of the 3' poly A tail in eukaryotic mRNA?
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stability, helps in translation
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T/F prokaryotic mRNA is postranscriptionally modified
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false. In prokaryotes, transcription and translation are coupled and occur simultaneosly. There is not time for post translational modification
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Explain how the poly A tail is added to eukaryotic mRNA
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-there is a signal in the 3' UTR that is recognized by poly A enzymes
-eznymes add up to 200 As |
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List the 3 important regions of a nacent transcript that are invovled in splicing
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1. 3' splice site
2. branch site A 3. 5' splice site |
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Explain the splicing reaction
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1. the 2'OH group on the branch site A attacks the phosphate group on the 5' splice site
2. The newly freed 3'OH group from the 5' exon attcks the phosphate group on the 3' splice site 3. the spliced lariat is left with a unique 2'-5' phosphodiester linkage |
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Describe the role of each of the following components of the splicesosomes (snRNPS)
U1, U2, U6 |
U1- binds the 5' splice site
U2- binds the branch site and associates with U1 to bring the 5' and 3' ends of the intron together U6- along with U2, form catalytic center to allow branch site A to attack 5' splice site Note: RNA molecules preform keys roles in positioning the transcript and catalyzing the splice |
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Wha three compoents are required for an operon to have transcriptional control
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1. regulatory gene
2. promoter 3. operator |
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explain how inducers regulate operons
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Inducers bind to the repressor to weaken the affinity for the promoter. This allows the operon to be turned on (it's ground state is off)
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Why must the lac repressor be consitutively expressed
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the lac operon needs to be keep on the off position unless its genes are needed. Consitual expression of the repressor ensures that the operon stays off. Control is exhibited at the level or inducer transcription. When the inducer is produced, it binds to the repressor and removes the repressor from the promoter site
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Explain the cascade that occurs when glucose is used up and E. coli needs to turn the lac operon on
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1. when glucose decreases cAMP increases
2. cAMP bins to CAP 3. cAMP-CAP binds to the operon promoter which brings RNA polymerase t othe promoter **in a separate pathway, the inducer is produced band binds the repressor to remove it from the operator Thus two things must happen for efficent transcription 1. release repressor 2. add CAP |
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What would be the state of the lac operon when there is both glucose and lactose in the media
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off because CAP would note be bound to the promoter because cAMP is not high because glucose is present
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What would be the state of the lac operon when glucose is present and lactose is absent
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Off because
1. lac repressor is bound (minimal lactose breakdown is required to make allolactose which is the inducer that removes the repressor) 2. Glucose is high so camp is low so cAMP-CAP is not bound to the promoter |
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What would be the state of the lac operon when both glucose and lactose are absent
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Off because the lac repressor is bound (no allolactose to induce)
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What would be the state of the lac operon when gluocose is absent and lactose is present
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ON
-lactose metabolism produces allolactose which induces the operon by removing the repressor -lack of glucose increases cAMP which binds to CAP and recruits RNA pol to the promoter |
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Describe the basal transcription machinery needed to transcribe all eukaryotic genes
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the machinery that binds to the core promoter
consists of RNA pol III and general transcription factors such as the TATA binding protein |
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Describe the role of regulating proteins in eukaryotic gene expression
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bind to enhancer sequences or silencer sequences acting at a distance to control gene expression
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Describe the role of coactivators in control of eukaryotic gene expression
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serve as scaffolding to link the basal transcriptional apparatus to upstream regulatory proteins
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Described the "ordered assembly" of the basal transcription factors in eukaryotic transcription
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1. The TATA binding protein binds the promoter and is followed by other factors
2. RNA polymerase II is recruited to the promoter 3. The C terminal domain of RNA pol II is phosphorylated and transcriptional elongation begins |
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What is the rate limiting step of transcription
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formation of the preinitation complex. enhances and enhancer binding proteins increase the rate of transcriptional initiation
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What three domains are usually present in eukaryotic transcription factors
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1. DNA binding
2. factor dimerization 3. transcriptional activation |
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List 4 ways a negative regulator may reduce gene expression in eukaryotes
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1. bind to DNA and block the bindng of a positive factor
2. bind to a positive transcription factor to prevent its binding to DNA or to speed degradation 3. inhibit binding or assembly of the pre-initiation complex 4. a negative factor may recruit hsitone deacetylases which cause the chromatin to repack |
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Compare and contrast the stucture of the prok and euk ribosomes
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prok- 70s, 30s + 50s
euks 80s, 60s + 40s (hint: proks are odd, all start with an odd number, euks are even) |
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List the 4 core properties of teh genetic code
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1. it is specific, the same codon always codes for the same amino acid
2. it is universal 3. it is redundant, a given amino acid may have more than one codon 4. it is non-overlapping |
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Describe each of the following mutations
silent missense nonsense |
silent-codon is changed to another codon that codes for the same amino acid
missense- codon is change to a codon that codes for a different amino acid nonsense- codon is changed to become a termination codon |
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describe the wobble hypothesis
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tRNA's wobble at the 5' end of the anticodon which pairs with the 3' end of the RNA. This allows for nontraditional base paring which explains why there doesnt need to be 61 unique tRNAs to read the 61 codons (eg UAU and UAC wobble at the third position allowing both to call for the same anticodon, thus the same tRNA and same amino acid)
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what are suppressor tRNAs
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tRNAs with mutated anticodons that incorporate an amino acid at termination codons, they supress the normal terminatino of a protein
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Describe the reaction that charges tRNAs
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-catalyzed by aminoacyl tRNA synthetase
-amino acid+ tRNA+ATP= aminoacyl-tRNA +amp+ PPi -the carboxy end of the amino acid attachs the ATP that is attached to adenine -The aminoacyl-AMP then attacks the phosphate group on the tRNA, an esterification reaction |
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What mechanism ensures that the correct start site is recognized in prokaryotic protein synthesis
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The 16s rRNA compoent of the 30s ribosomal subunit reconizes the shine-delgarno sequence in the mRNA. Base pairing of the 16s with the transcript positions the ribosome at the correct AUG start site. Then the initiator tRNA with the help of IF-2 brings N-formyl methionine to the P site
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what role does IF 3 play in the initiation of prok protein synthesis
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IF3 keeps the 30s and 50s subunits apart so that the 30s sequence can recongize the initiation codon
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Describe the role of EF-Tu and EF-Ts in the elongation of prokaryotic proteins
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EF-Tu brings the aminoacyl tRNA in from the cytoplasm. Hydrolysis of GTP releases the tRNA from EF-Tu allowing the tRNA to enter the A site. EF-Ts acts as a nucleotide exchange factor for EF-Tu. EF-Ts releases GDP from EF-Tu allowing Tu to get a new GTP so it can repeate the reaction
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What component of the 50s ribosome catalyses the formation of the peptide bond in prokaryotes
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23S rRNA
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Describe how an amino acid is added to a growing peptide chain
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The tRNA brings the amino acid to the A site. The rRNA catalyzes the formation of a peptide bond between the A site amino acid and the chain in the P site. The chain is then transfered to the tRNA in the A site. After the bond is formed, the ribosome translocates (facilitated by EF-G and hydrolysis of GTP) and the chain is moved to the P site.
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What role does EF-G serve in prokaryotic protein elongation
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EF-G binds GTP which is required for translocation of the ribosome after a new peptide bond is formed
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Describe how protein synthesis is terminated
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When a stop codon is reached, a release factor binds to the codon (instead of a tRNA). The RF makes the peptidyl transferase add water instead of an amino acid to the chain which results in hydrolysis and release.
Do not confuse this with protein independent/ dependent termination of transCRIPTION! |
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Describe the components of the ternary complex and how it regulates euakryotic protein synthesis initiation
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The ternary complex consists of ELF2, GTP, and the tRNA with methionine on it. ELF2 must be in GTP bound form for the complex to form. IF ELF2 is phosphorylated, it won't give up GTP and the 43S preinitiation complex cannot form.
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What is the role of ELF2B in the initation of eukaryotic protein synthesis
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ELF2B is a guanine nucleotide exchange factor for ELF2. ELF2+GTP helps bring the met-tRNA to the preinitiation complex. WIthout ELF2B GTP could not be generated and the 43S preinitation complex could not form
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Proks use the 16s rRNA and the shine delgarno sequence to find the appropriate AUG start site. How do euks find the right AUG
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The 40s ribosome loads at the 5' end of the mRNA and looks for the first AUG (ATP dependent). There also may be some regulation by the Kozak sequence
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What role does ELF4E play in eukaryotic protein synthesis initiation
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ELF4E binds to the 5' cap of the mRNA and promotes binding to the 40s subunit. It needs to be phsophorylated to be active providing a mechanism for regulation
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Polio virus causes the proteolysis of ELF4E. How would this affect eukaryotic protein synthesis
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ELF4E is required to bind the 5' cap of mRNA and load it into the 40s subunit. WIthout this factor, mRNA is not properly translated
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How does diptheria toxin inhibit eukaryotic protein synthesis
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The toxin ADP ribosylated EF2 translocates which inhibits ribosome translocation and thus protein synthesis
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list 5 post translational modifications of proteins
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1. proteolytic processing (zymogens)
2. phosphorylation 3. glycosylation 4. hydroxylation 5. ubiquitination others include: carboxylases in RER, lipid modifications, farnesylation, palmitoylation |
