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CH 6 Genetics
DNA
| Question | Answer |
|---|---|
| Components of DNA | deoxyribose sugar, phosphate, and one of four nitrogenous bases ATGC |
| How are the carbons of deoxyribose sugar distinguished from the atoms within the nucleotide base? | By the use of primed numbers from 1' to 5' |
| Where is DNA found? | in the nucleus and it's acidic |
| DNA has ____________ subunits | nucleotide |
| WHat does DNA look like? | a double helix with two chains spiraling around an axis with the sugar-phosphate backbones on the outside and the flat pairs of bases meeting in the middle |
| In which direction does the upward chain of DNA run? | 5' to 3' |
| In which direction does the downward chain of DNA run? | 3' to 5' |
| The 2 spiraling structures of DNA are composed of _____-______ backbones | sugar phosphate |
| The rungs of the ladder of DNA are composed of the _______ _____. | base pairs |
| The _______________ of the backbone creates two grooves (major and minor) | displacement |
| Major groove | wider |
| minor groove | thinner |
| What are the two chains of a double helix held together by? | hydrogen bonds between complementary base pairs that help create chemical stability |
| What are the base pairs of DNA? A:___ and G:___ | A:T and G:C |
| The MAJORITY of DNA is found in the B-Form which means it | spirals to the right. |
| The other form is called Z form for zigzag because it | spirals to the left in a zigzag shape. |
| T/F The biological role of these 2 forms (B/Z) has not yet been determined. | True |
| T/F All eukaryotic organisms have long, linear chromosomes (double helixes) | True |
| RNA is a _______ stranded molecule that has the sugar ______, has the base ________instead of thymine (T). | single, ribose, Uracil (U) |
| U base pairs with ____ | A |
| Why is RNA single stranded? | so they contain far fewer nucleotides to form single-stranded loops which makes them much less stable than DNA |
| What is a purine? | adenine (A) and guanine (G), which have a double-ring structure. (Numbered 1-9) |
| What is a pyrimidine? | cytosine (C) and thymine (T), which have a single-ring structure |
| Is Uracil a pyrimidine or purine? | pyrimidine |
| T/F Uracil is only found in RNA | True |
| How are nucleotides connected within a DNA polymer? | Connected in 5’ to 3’ direction, covalent bonds at bases jutting outwards. |
| Nucleotides in a DNA polymer are connected by ______________ bonds which form a sugar-phosphate backbone. | phosphodiester |
| How is DNA organized within a double helix? | Dna Is found double stranded. |
| What is meant by antiparallel? | Antiparallel means one chain runs in one direction 5’ to 3’ while the other chain runs in the opposite direction 3’ to 5’ |
| What is the major groove? | Wider space between the two strands |
| What is The minor groove? | Thinner space |
| What is the significance of each of the grooves? | Even though the bases are inside and they’re hydrogen bonded to one another there’s enough access to those bases. |
| Even though the major and minor groove strands are not separated, | proteins interact with DNA based on the DNA bases and different sequences of DNA. |
| How do base pairs bond between the G and C DNA strands? | have 3 hydrogen bonds |
| How do base pairs bond between the A and T DNA strands? | have 2 hydrogen bonds |
| There is only enough space in DNA formation for one _____ and one pyrimidine | purine |
| B-DNA is the | most common, right-handed form under normal physiological conditions |
| A-DNA is __ ___ _____ ___ __, often formed under ______ conditions or in DNA/RNA _____ | a shorter, wider right-handed helix,, dehydrating, hybrids |
| Z-DNA is __ ____-_____ ____ often formed with alternating GC sequences under ____ ____ _________ or specific biological conditions like a test _____. | a left-handed helix, high salt concentrations, tube |
| How do DNA binding proteins recognize different DNA bases when the double helix is intact? | Through those major grooves |
| Does RNA ever function as genetic material? | Yes only in Retroviruses (never in living things) |
| in DNA replication, Strands separate then each of the ______ strands serve as templates for DNA polymerase to make 2 _______ helixes/complimentary strands.? | parent, daughter |
| What is the mechanism of DNA replication? | Initiation unwinds the double helix and elongation where DNA polymerase III synthesizes the leading strand while the lagging strand is made in okazaki fragments. |
| What enzyme covalently joins successive okazaki fragments into a continuous strand of DNA? | DNA ligase |
| What enzyme unwinds the double helix progressively? | helicase |
| T/F DNA polymerase moves in the same direction as the fork to synthesize the leading strand? | True |
| What is meant by semi-conservative replication? | the daughter strands lined up as one whole parent strand and one newly synthesized strand at the end |
| What provides the energy for DNA replication? | the bases themselves that come in as high energy triphosphates |
| What is a replication fork? | As a replication bubble opens up, 2 replication forks (Y shaped) take off in opposite directions. DNA replication starts at one point then proceeds in 2 different directions |
| Okazaki fragments | The lagging strand is synthesized discontinuously as small fragments of about 1000 bases |
| How is each okazaki fragment initiated? | by a short RNA primer made by primase |
| What role does helicase play in DNA replication? | Helicase opens things up |
| Single stranded binding proteins | come in and keep the strands separated from one another. |
| RNA primase | lays down a primer to get things going |
| DNA polymerase needs a | free OH group to get started |
| DNA polymerase III | Synthesizes the leading strand |
| DNA Polymerase I | replaces the RNA primers with DNA |
| DNA topoisomerases help | relax the supercoils by nicking one or cutting both strands of the DNA. (found in DNA replication in E. coli…) |
| *only thing to Know about replication in E. coli is it has a | single start site |
| whereas in eukaryotic cells because the DNA is so large there is many _______ of replication to get things started in order to____ ___ ______ __________ | origins, copy the entire chromosome |
| In most cases a single start site will generate __ replication forks | 2 |
| Telomers: | the ends of a chromosome that the cell needs because the lagging strands make copying the ends of a chromosome difficult |
| Telomeres ensure the maintenance and accurate replication of | the 2 ends of each linear chromosome |
| In a general sense, what happens during crossing-over? | Two homologous chromosomes can exchange parts, which can generate new allelic combinations of syntenic genes |
| What is a holiday junction? | where part of one chromosome has made its way to another chromosome |
| What are holiday junctions needed for? | to zip and then branch migration can occur once the chromosomes line up during meiosis |
| In holiday junctions, DNA ligase forms _____________ bonds b/t the adjacent ends to rejoin DNA strands without the ____ or ____ of nucleotides | phosphodiester, loss or gain |
| What shape are Holiday Junctions? | X |
| Branch migration thus _________ the heteroduplex region of both DNA molecules from tens of base pairs to hundreds or thousands | lengthens |
| What is gene conversion? | a genetic process where one DNA sequence is non-reciprocally copied to another, altering its sequence |
| Gene conversion is a byproduct of the DNA repair mechanisms that fix double strand breaks during _______ recombination | meiotic |
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