Genetics Exam 3 Study Guide
Genetics Exam 3 Study Guide BSCI - 30156 - 002
Popular in ELEMENTS OF GENETICS
BSCI - 30156 - 002
verified elite notetaker
Popular in Biological Sciences
This 8 page Study Guide was uploaded by Jessica Brown on Monday April 11, 2016. The Study Guide belongs to BSCI - 30156 - 002 at Kent State University taught by Chi-hua Groff (P) in Fall 2015. Since its upload, it has received 41 views. For similar materials see ELEMENTS OF GENETICS in Biological Sciences at Kent State University.
Reviews for Genetics Exam 3 Study Guide
Report this Material
What is Karma?
Karma is the currency of StudySoup.
You can buy or earn more Karma at anytime and redeem it for class notes, study guides, flashcards, and more!
Date Created: 04/11/16
Genetics Exam 3 Study Guide Highlight: definition Highlight: question Highlight: important information DNA Replication DNA Replication: genetic material is transmitted from parent to offspring and from cell to cell, for this to occur genetic material must be copied DNA is a double helix o Two strands are held together in the helix by hydrogen bonds o The strands have an antiparallel alignment During DNA replication the two strands separate o One becomes the template strand and one becomes the parental strand o The two new strands are the daughter strands DNA replication is semiconservative o This means that the double stranded DNA is half conserved following the replication process This means the newly made double stranded DNA contains one parental strand and one daughter strand Origin of Replication: This is where DNA synthesis begins o Bacterial chromosomes have one origin of replication The synthesis in bacteria occurs bidirectionally Replication Fork: Where the parental DNA strands have separated and new daughter strands are being made o In bacteria the two replication forks move in opposite directions DNA replication is initiated by DnaA proteins binding to sequences in the origin known as DnaA box sequences o DnaA Box Sequences: a recognition site for the binding of DnaA proteins o DNA Helicase: breaks hydrogen bonds between two strands of DNA o DNA Primase: Synthesizes an RNA primer The primase allows the polymerases to start synthesizing the daughter strands RNA Primer is placed at the origin of the leading strand RNA primers are removed and the DNA fragments must be joined to form a continuous strand and complete replication o DNA Ligase: covalently links the okazaki (DNA) fragments together o DNA Polymerase 1: excises the RNA primers and fills in with DNA Removes RNA fragments o DNA Polymerase 3: synthesizes a daughter strand of DNA Conducts a majority of replication DNA polyermases attach new nucleotides in the 5’ to 3’ direction DNA Polymerases require shorter strands of RNA In the lagging strand replication occurs away from the replication fork but it is still in the 5’ to 3’ direction o Only short fragments of nucleotides are attached at one time (1,000- 2,000) o Each fragment will contain a short RNA primer at the 5’ end These fragments are known as okazaki fragments Homologous Recombination Recall recombination from the last exam o Creates genetic diversity o Separates mutations that can have severely deleterious effects and brings together combinations of mutations that when combined can be beneficial Genetic recombination: the process in which chromosomes are broken and rejoined to form new genetic material o Homologous recombination occurs between genetically similar sequences Holliday proposed the mechanism to explain the molecular steps of homologous recombination o This is known as the Holliday Model Illustrated in figure 13.24a Holliday Junction: formation of a covalent linkage Isomerization of the strands prevents breaks in the same strand that were originally broken as they separate from the junction Branch Migration: A DNA strand in one helix is swapped with the DNA strand in the other helix. These produce regions in DNA called heteroduplexes Resolution: recreates two separate chromosomes Gene Conversion Gene conversion: one allele is converted to the allele on the homologous chromosome The transfer is unidirectional o This means that if one allele has a mutation that is harmful, it can be transferred by gene conversion to the second allele Gene Transcription and RNA Modification Transcription is the first step in extracting the information from a primary DNA sequence DNA sequences provide the information for transcription o Variation (mutation) always happens at the level of DNA replication Proteins must interact with the DNA sequences to regulate transcription o Recall: heterochromatin and euchromatin. Euchromatin is the open form and the only one that proteins can interact with RNA: a single strand or chain of nucleotides. Composed of a base sugar and the phosphate group. RNA is composed of 4 bases—A, G, C and U o U replaces what would be a T in DNA Making RNA occurs through transcription o Transcription begins within the nucleus of a cell o The first step involves separating DNA into two separate strands This requires breaking of hydrogen bonds Question: What is required to break hydrogen bonds? One of the two strands is a template—this strand is used to help RNA correctly pair bases (G with C and U with A) o Stages of transcription: Initiation, Elongation, and Termination. All of the stages will require protein to interact with the DNA o RNA Polymerases RNA polymerase 1: used to transcribe ribosomal (rRNA) genes RNA polymerase 2: used to transcribe all structural genes (mRNA) RNA polymerase 3: used to transcribe transfer RNA (tRNA) Eukaryotic Structural Genes o Eukaryotic promoter: contains a transcriptional start site—this is known as the TATA box—and a regulatory elements o Core Promotor: short and consists of a TATAAAA sequence This sequence is known as the TATA box TATA box usually contains about 25 base pairs o This will determine where transcription starts Basal Transcription: when the core promotor produces a low level of transcription on its own Regulatory elements will influence whether the RNA polymerase to recognize the core promotor o Enhancers: activating sequences o Silencers: repress transcription o Regulatory Transcription Factors: proteins that will bind to regulatory regions Regulatory elements can be located a good distance from the gene that is in the process of being transcribed o Cis-Acting Elements: Things that have the ability to influence a nearby gene TATA Box, enhancers, and silencers are known as cis acting elements o Trans-Acting Elements: these are produces by regulatory genes. They can be located a good distance away from the gene being transcribed RNA Modifications 5’ caps and 3’ tails Capping: Mature mRNA’s will have a 7-methylguanosine cap at the 5’ end. o This gives certain RNA’s the ability to exit the nucleus o The cap begins and is involved early in translation o Also can be involved with splicing introns at the 5’ end PolyA tail: added to the 3’ end and occurs by a string of adenine nucleotides being added o This requires a polyadenylation sequence o Important for the stability of mRNA PolyA-binding proteins recognize the poly A tail to promote this stability The length of the tail will affect how stable the mRNA ends up o Newly transcribed mRNA has a polyA tail that averages 200 nucleotides o As mRNA ages, cellular exonucleases shorten the polyA tail Once shortened down to 10-30 nucleotides, the polyA binding proteins can no longer bind and the mRNA is degraded very quickly Reverse transcription: can take processed mRNA molecule and turn it to a double stranded RNA/DNA hybrid that cannot be translated and can be integrated anywhere in the genome. A special reverse transcription polymerase is used to achieve this. o Processed Pseudogene: Since this sequence has already been spliced it is shorter than that of the original locus These can have negative effects such as over production of a protein. This is due to the pseudogenes having an open reading frame intact that is able to be transcribed and translated Splicing Eukaryotic organisms have coding sequences (exons) and intervening sequences (introns) o Introns were first detected by comparing the base sequences of genes with the base sequences of mRNA Transcription makes the entire gene sequence, the introns are then removed and the exons are spliced together in a process known as RNA splicing Alternative Splicing Alternative splicing can procude several different patterns of exons in mRNA o This produces proteins with differences in amino acid sequences May cause slight variation in protein function, which could be important during embryotic life and development. Constitutive exons: marked this if they are not detected as being spliced out by a splicing reaction o Ex.) first or terminal exons o Always found in mature mRNA o Alternate exons are not always found in mRNA Translation RNA Protein Occurs in the cytoplasm Involved interactions of mRNA, tRNA and rRNA Know how to read the genetic code table!! (How to tell what codons produce what proteins) Degenerate genetic code: when more the one codon specifies for the same amino acid Cells contain many tRNA molecules (anticodon sequences) o Anticodon is a three nucleotide sequence that is complementary to each codon (following base pairing rules) o Each tRNA carries one of the 20 amino acids o Binds to the mRNA via base pairing and the tRNA “drops off” the amino acid o First codon in any living organism is “AUG”. The tRNA carries the anticodon “UAC” (methionine). Therefore, the first amino acid of any protein is methionine Translation continues as the ribosome moves along the mRNA one codon at a time. o Process will stop when the ribosome comes to a “stop” codon There are 3 stop codons—refer to the genetic code table Once this occurs translation ends and mRNA and the ribosome separate Ribosome is the site of translation in both bacterial and eukaryotic cells o They have discrete sites (P,A,E) Translation has three stages o Initiation Involves the binding of mRNA, tRNA and ribosomal subunits o Elongation Adds amino acids, one at a time to the polypeptide chain. It does this in steps A charged tRNA binds to the A site The enzyme peptidytransferase catalyzes bond formation between the polypeptide chain and the amino acid that is currently in the A site The ribosome trans locates one codon to the right (3’) The uncharged tRNA is released from the E site Process is repeated until a stop codon is reached o Termination Occurs once a stop codon is reached Translation is complete Directionality of the polypeptie chain o Has directionality that parallels the mRNA chain o The first amino acid of the polypeptide is considered to be at the N- Terminal end (or amino terminal end) o The last amino acid is considered to be at the C-Terminal end (or the carboxyl terminal end) Protein Structure o The net result of transcription and translation is a polypeptide with a define amino acid sequence This sequence is known as the primary structure o To become functional the polypeptides must fold and become 3D Structure and function of tRNA Functions o Recognizes codons within mRNA and carry out the correct amino acid to the site of polypeptide synthesis o Binds to mRNA as an anticodon during mRNA-tRNA recognition Structure o Three stem loop structure o Contains a variable region o An acceptor with a 3’ single stranded region Aminoacyl-tRNA Synthetases o An enzyme that catalyzes the attachment of amino acids to the 3’ end of the tRNA About 20 different forms of this enzyme per one amino acid Once the amino acid is attached to the tRNA it is referred to as a charged tRNA Wobble Rule o Genetic code is degenerate. o For most amino acid codons the third base is not crucial to identifying the amino acid. Transcription Factors Transcription factors: proteins that influence the ability of the RNA polymerase to transcribe a gene o General transcription factors take the RNA polymerase and bind it to the core promotor o Regulatory transcription factors regulate the rate of gene transcription Domains: regions of transcription factors that have specific functions Motif: a domain that has similar structure in many different proteins Regulatory transcription factors can be enhancers or silencers If they up-regulate they are enhancers If they down-regulate they are silencers Orientation independent or bidirectional Proteins typically recognize cis regulatory sequence elements o Noncoding DNA sequences are called response, control, or cis regulatory elements. These are the “on/off” switches we learned about in the first module Activators: increase the rate of transcription o Enhancer: is the DNA sequence that the activator binds to Repressors: decrease the rate of transcription o Silencer: the DNA sequence that the repressor binds to Homodimer: two identical transcription factors that come together Heterodimer: two different factors that interact TATA box binding Factor (TF11D) and Mediator Most regulatory transcription factors do not bind directly to RNA polymerases, instead they interact with either (TF11D) or the mediator o Activator proteins increase rate of transcription by interacting with the coactivators but do not bind to the DNA itself o Repressors inhibit the rate of transcription by binding to the TF11D Modulating Regulatory Transcription Factor Function Regulatory transcription factors must be regulated for the same reasons as genes Three basic mechanisms of regulation 1. Binding of an effector molecule (ex.) steroid hormones) a. Steroid Receptors: Regulatory transcription factors that interact with steroid hormones i. Synthesized by endocrine glands SNP’s and their Influence on gene expression SNP’s occur during errors in DNA replication Transcription o SNP’s in cis-regulatory sequences (enhancers, silencers, promotors) can impact the transcriptional activity of a locus Occurs at low rates o Introns don’t have a function so SNP’s occurring here are neutral and occur at neutral rates Splicing o SNP’s occurring in the 5’ GT or 3’ AG consensus splicing acceptor and donor sites are occurring at very low rates because they can be highly deleterious. o SNP’s can occur in exons and create cryptic GT and or AG sites o SNP’s occurring in the third position of a codon occur at a faster rate than those in the first position of a codon o SNP’s occurring in the coding region can lead to a stop codon This would be considered a nonsense mutation o SNP’s that lead to a change in amino acid sequence (nonsynonymous) occur at a lower rate then synonymous Population Genetics Population: group of individuals of the same species that can interbreed with one another o Genetic Polymorphism: observation that many traits display variation within a population This is caused by two or more alleles for a trait in a population (polymorphic) o Monomorphic trait: exist in single allele in the population Found in 99% of the population o SNP’s (single nucleotide polymorphisms): single nucleotide differences in alleles of a gene Very common in a population Go over and understand how to do Hardy-Weinburg problems!
Are you sure you want to buy this material for
You're already Subscribed!
Looks like you've already subscribed to StudySoup, you won't need to purchase another subscription to get this material. To access this material simply click 'View Full Document'