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Genetics Chapter 8
DNA: the chemical nature of the gene
| Question | Answer |
|---|---|
| the coding instructions of all living organisms are written in the same genetic language- that of ________ _____ | nucleic acids |
| genetic material possesses three key characteristics: | (1) must contain complex information (2) must replicate accurately (3) must have to ability to be translated into the phenotype |
| all genetic information is encoded in the structure of ___ | DNA |
| DNA consists of a large number of linked, repeating units called ___________ | nucleotides |
| what three things do each nucleotide contain? | a sugar, a phosphate, and a base |
| the first clue that DNA was a carrier of hereditary information came with the demonstration that DNA was responsible for a phenomenon called __________ | transformation |
| this phenomenon was first observed in 1928 by ____ _______ | Fred Griffith |
| In Griffith's experiment, a virulent bacteria caused death. Heat-killed vir. bacteria did not. The combo of heat-killed vir. bacteria with nonvir. bacteria also caused death. conclusion? | a substance in the heat-killed virulent bacteria genetically transformed the type IIR(nonvirulent) bacteria into live, virulent type IIIS bacteria |
| Griffith didn't understand the nature of transformation but theorized that some substance in the polysaccharide coat of the dead bacteria might be responsible. He called this substance the ___________ _________ | transforming principle |
| Who were three scientists who experimented to reveal the nature of the transforming substance? | Avery, MacLeod, and McCarty. |
| Avery, MacLeod and McCartney used enzymes in their experiment. What three did they used and what do these enzymes 'destroy'? | RNase(destroys RNA), Protease(destroys proteins), and DNase(destroys DNA) |
| In their experiment, they treated heat-killed virulent bacteria (IIIS) with the three enzymes. What were the results? | the cultures treated with RNase and Protease contained transformed type IIIS bacteria while the culture treated with DNase only contained the nonvirulent IIR bacteria. |
| What did Avery, MacLeod, and McCarty conclude with their experiment? | Because only DNase destroyed the transforming substance, the transforming substance, (and genetic information) must be DNA |
| What question did Hershey and Chase set out to answer in their experiment? | which part of the phage, its DNA or its protein, serves as the genetic material and is transmitted to phage progeny? |
| They used a T2 phage which infects what? | E. coli |
| using radioactive ________, Hershey and Chase traced the movement of DNA and protein during phage infection | isotopes |
| Which two radioactive isotopes did they use? | S^35 and P^32 |
| First they grew E.coli in a S^35 medium and E.coli in a P^32 medium. They then infected each E. coli with the T2 phages. What happened? | the phages that infected the E.coli grown in S^35 medium took up S^35 in the phage protein(which contains S but not P), while the phages that infected the E.coli grown in the P^32 medium took up P^32 in the phage DNA (which contains P but not S) |
| They then took these two phages (one containing the S^35 and one containing the P^32) and again infected E.coli with each strain separately. They sheared off phage ______ coats in a blender and separated then from the cells by centrifuging. | protein |
| After centrifugation, S^35 and P^32 were recovered then they tested each progeny phage for radioactivity. What did they find in the S^35 progeny? | that no radioactivity was detected, indicating that protein has not been transmitted to the progeny phages. |
| After centrifugation, S^35 and P^32 were recovered then they tested each progeny phage for radioactivity. What did they find in the P^32 progeny? | the progeny phages were radioactive, indicating that DNA had been transmitted to progeny phages |
| What did Hershey and Chase conclude from their experiment? | that DNA, not protein, is the genetic material in bacteriophages |
| Ashbury began studying the three-dimensional structure of DNA by using a technique called _-___ _________ | X-ray diffraction |
| how does x-ray diffraction work? | x-ray beamed at a molecule are reflected in specific patterns that reveal aspects of the structure of the molecule |
| ashbury's diffraction pictures did not provide enough resolution to reveal the structure. Whom else used X-ray diffraction to get strikingly better pictures of the molecule? | Franklin |
| Which two people developed a three-dimensional model of the structure of DNA using the x-ray diffraction photographs taken by Franklin? | Watson and Crick |
| What other resources did Watson and Crick use? | existing information about the chemistry of DNA and molecular models |
| It is useful to consider the structure of DNA at three levels of increasing complexity: | primary, secondary, and tertiary |
| DNA: primary structure refers to what? | DNA's nucleotide structure and how the nucleotides are joined together |
| DNA: secondary structure refers to what?> | DNA's stable 3D configuration (helical structure) |
| DNA: tertiary structure refers to what? | complex packing arrangements of double-stranded DNA in chromosomes |
| Primary: DNA is a ______, meaning that it is a chain made up of many repeating units linked together | polymer |
| Primary: what are these repeating units? | nucleotides |
| Primary: what three things do nucleotides contain? | a 5 carbon sugar, a phosphate, and a nitrogen-containing base |
| the sugars of nucleic acids are called ______ sugars | pentose (because of the 5 carbons) |
| the sugars of DNA and RNA are slightly different in structure. RNA's sugar is called _______ and DNA's sugar is called ___________ | ribose, deoxyribose |
| explain the structure of ribose, RNA's sugar | it has a hydroxyl group (-OH) attached to the 2' carbon |
| explain the structure of deoxyribose, DNA's sugar | it has a hydrogen atom (-H) attached to the 2' carbon (one less oxygen atom than ribose) |
| what difference does the extra oxygen molecule in ribose make between RNA and DNA? | makes RNA more reactive and less chemically stable than DNA. (This is why DNA is better suited for long term repository of genetic info) |
| the nitrogenous base of nucleotides can be one of two types. a _____ or a ________ | purine, pyrimidine |
| explain the structure of a purine | a six-sided ring attached to a five-sided ring |
| purines include what? | adenine and guanine (A and G) |
| explain the structure of a pyrimidine | a six sided ring |
| pyrimidines include what? | cytosine (C), thymine (T), and uracil (U) |
| both DNA and RNA contain the two purines. For the pyrimidines however, _______ is present in both DNA and RNA, _______ is restricted to DNA and _______ is restricted to RNA | cytosine, thymine, and uracil |
| the three pyrimidines differ in what two things? | groups (or atoms) attached to the carbon atoms of the ring and number of double bonds in the ring |
| in a nucleotide, the nitrogenous base always forms a covalent bond with which carbon atom of the sugar? | the 1' carbon |
| a deoxyribose or ribose sugar together with a base is referred to as a ________ | nucleoside |
| the phosphate group of nucleotides consists of what? | a phosphorus atom bonded to 4 oxygen atoms |
| phosphate groups are found in every nucleotide and frequently carry a _______ charge, which makes DNA acidic | negative |
| Which carbon atom of the sugar is the phosphate group always bonded to? | the 5' carbon |
| DNA nucleotides are called what? | deoxyribonucleotides |
| DNA: because there are four types of bases (A, G, T, and C) there are four different kinds of nucleotides. What are they called? | dAMP, dGMP, dTMP, and dCMP |
| DNA is made up of many nucleotides connected by _______ bonds | covalent |
| the covalent bonds link together what? | the 5'-phosphate group of one nucleotide to the 3'-carbon atom of the next nucleotide |
| these strong covalent bonds are called ___________ ________ | phosphodiester linkages |
| a series of nucleotides linked in this way makes up a _____________ ______ | polynucleotide strand |
| the backbone of the polynucleotide strand is compose of alternating what? | sugars and phosphates |
| the bases project _____ from the long axis of the strand | away |
| an important characteristic of a polynucleotide strand is its direction, or _______ | polarity |
| 5' end of a polynucleotide chain | where a phosphate is attached to the 5' -carbon atom |
| 3' end of a polynucleotide chain | where an OH group is attached to the 3' -carbon atom |
| The secondary structure of DNA refers to its 3D configuration. This structure can assume a variety of configurations, depending on its what? | base sequence (and the conditions in which it is placed) |
| what makes the double helix structure? | two polynucleotide strands wound around each other |
| the two polynucleotide strands run in opposite directions and are said to be ___________ | antiparallel |
| explain how they are antiparallel | the 5' end of one strand is opposite of the 3' end of the other strand |
| the strands are held together by two types of molecular forces. What are they? | hydrogen bonds and the interaction between the stacked base pairs |
| the hyrdogen bonds link what? | they link the bases on OPPOSITE strands |
| the phosphodiester bonds link connect what? | they connect the sugar and phosphate groups of adjoining nucleotides on the SAME strand |
| Which bond is weaker? | hydrogen bond |
| the nature of hydrogen bond imposes limitations on the types of ____ it can pair | bases |
| Adenine normally only pairs with ________ through _#_ hydrogen bonds | thymine, 2 |
| cytosine normally pairs only with _______ through _#_ hydrogen bonds | guanine, 3 |
| With these specificity of the base pairings, the two polynucleotide strands of a DNA molecule are not identical but are ___________ DNA strands | complementary |
| the stacking interactions between base pairs contribute to the _________ of the DNA molecule | stability |
| the stacking interactions do not require that any particular base follow another. the base sequence of the DNA molecule is then free to v___, allowing DNA to carry genetic information | vary |
| DNA normally consists of two polynucleotide strands that are antiparallel and complementary. The precise 3D structure can vary depending on the _________ in which the DNA is placed and in some cases on the _____ _________ itself | conditions, base sequence |
| the 3D structure of DNA described by Watson and Crick is termed the __-DNA structure | B-DNA |
| Explain the conditions in which B-DNA exists in | plenty of water surrounds the molecule and there is not unusual base sequence in the DNA |
| the B-DNA structure is the most ________ configuration for a RANDOM sequence of nucleotides under physiological conditions | stable |
| B-DNA is an ALPHA helix, meaning that is has a _____-handed, or _______ spiral | right, clockwise |
| B-DNA: there are approximately _#_ base pairs per 360 degree rotation of the helix | 10 |
| B-DNA: the spiraling of the nucleotide strands creates what kind of grooves in the helix? | major and minor |
| Another secondary structure that DNA can assume is the __-DNA structure, which exists if less water is present | A-DNA |
| A-DNA is an ____ helix | alpha (right-handed like B-DNA) |
| how does A-DNA differ from B-DNA? | A-DNA is shorter and wider and its bases are tilted AWAY from the main axis of the molecule |
| a radically different secondary structure is called __-DNA | Z |
| Z-DNA forms a ____-handed helix | left |
| describe the structure of Z-DNA | the sugar-phosphate backbone ZIGZAGS back and forth |
| a Z-DNA structure can result from what? | molecules containing particular base sequences (such as stretches of alternation G and C nucleotides) |
| researchers have suggested that Z-DNA could play some role in ____ ________ | gene expression |
| Chromosomal DNA exists in the form of very long molecules and must be what to fit into the small confines of a cell? | tightly packed |
| one type of DNA tertiary structure is ___________, which takes place when the DNA helix is subjected to STRAIN by being overwound or underwound | supercoiling |
| the lowest energy state for B-DNA is when it has about _#_ bp per turn of its helix. This is called the ______ state | 10, relaxed |
| if energy is used to add or remove any turns, _____ is placed on the molecule, causing the helix to supercoil, or twist, on itself | strain |
| molecules that are overrotated exhibit _______ supercoiling | positive |
| underrotated molecules exhibit ________ supercoiling | negative |
| supercoiling relies on which enzyme? | topoisomerases |
| what does topoisomerase do? | ad or remove rotations from the DNA helix (by temporarily breaking the nucleotide strands, rotating the ends around each other, and then rejoining the broken ends) |
| topoisomerase can both _____ and _____ supercoiling | induce and relieve |
| most DNA found in cells is ________ supercoiled | negatively |
| what two advantages does negatively supercoiled DNA have over nonsupercoiled DNA? | it eases the separation of nucleotide strands during replication and transcription and allows DNA to be packed into small spaces |
| most bacterial chromosomes consists of a large ______ molecule of DNA that is a series of twisted loops | circular |
| bacterial DNA appears as what? | a distinct clump, the NUCLEOID, within the bacterial cell |
| what is the material that makes up eukaryotic chromosomes? | chromatin |
| what does chromatin consist of? | DNA and protein |
| what are the two basic types of chromatin? | euchromatin and heterochromatin |
| explain euchromatin in reference to the cell cycle | undergoes the normal process of condensation and decondensation in the cell cyle |
| explain heterochromatin in reference to the cell cycle | remains in highly condensed state throughout the cell cyle |
| what is is heterochromatin characterized by? | a general lack of transcription, the absence of crossing over, and replication in S stage |
| the most-abundant proteins in chromatin are the _______ | histones |
| histones | small, positively charged proteins |
| what are the five major types of histones? | H1, H2A, H2B, H3, and H4 |
| what holds the DNA in contact with the histones? | the histones' positive charge attract the negative charges on the phosphate of DNA |
| the repeating core of protein and DNA produced by digestion with nuclease enzymes is the simplest level of chromatin structure. What is this called? | nucleosome |
| nucleosome | a core particle consisting of DNA wrapped around eight histone proteins (2 copies of each: H2A, H2B, H3, H4) |
| nucleosomes bound to an H1 histone are called __________ | chromatosomes |
| chromatosomes are located at regular intervals along the DNA molecule and are separated from one another by _______ DNA | linker DNA |
| epigenetics | alterations of chromatin or DNA structure that do not include changes in the base sequence (are stable and passed on to cells or organisms) |
| centromere | region of chromosome of which spindle fibers attach |
| centromeric sequences | functional centromeres that allow segragation to take place |
| telomere | the stabilizing end of a chromosome |
| at the end of each telomere are many short ________ ________ | telomeric sequences |
| what do these telomeric sequences usually consist of? | repeated units of A or T nucleotides followed by G nucleotides: taking the form 5'-(A or T)mGn-3', m=1-4, n=2+ |
| a multiprotein called _________ binds to mammalian telomeres and protexts the ends of the DNA from being inadvertently repaired as a double-stranded break in the DNA | shelterin |
| eukaryotic organisms differe in the amount of DNA per cell, a quantity termed an organism's __-______ | C-value |
| eukaryotic DNA comprises three major classes: | unique-sequence DNA, moderately repetitive DNA, and highly repetitive DNA |
| Unique-sequence DNA consists of what? | sequences that exist in on or only a few copies |
| other genes within unique-sequence DNA are present in several similar, but not identical, copies and together are referred to as a _____ ________ | gene family |
| repetitive DNA | sequences that exist in many copies |
| moderately repetitive DNA consists of | sequences that may be several hundred base pairs in length and is present in thousands to hundreds of thousands of copies |
| moderately repetitive DNA is of two types of repeats: | Tandem repeat sequences and interspersed repeat sequences |
| tandem repeat sequences | appear one after another and tend to be clustered at particular locations on the chromosomes |
| interspersed repeat sequences | scattered throughout the genome |
| short interspersed repeats are called _____ | SINEs (short interspersed elements) |
| longer interspersed repeats consisting of several thousand base pairs are called _____ | LINEs (long interspersed elements) |
| highly repetitive DNA consists of | very short sequences repeated in tandem and present in hundreds of thousands to millions of copies |
| the d_______ of genes varies greatly among chromosomes | density |
| explain the DNA in cytoplasmic organelles | usually circular and not complexed to histone proteins |
Created by:
cmccartney2
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