Molecules (DNA and RNA)- topic 1

Question 1

what is the sub unit of nucleic acids?

Answer 1

• a nucleotide

Question 2

what are the three components of a nucleotide?

Answer 2

-a phosphate group
-a pentose sugar
-a nitrogenous base

Question 3

how are the components of a nucleotide bonded, what reaction ?

Answer 3

-the three components are combined via condensation reactions

Question 4

what is the bond that links the pentose sugar to the phosphate group? what does this mean in relation to other nucleotides?

Answer 4

-phosphodiester bonds
-these bonds in effect join adjacent nucleotides together again through their condensation reactions prior to this

Question 5

how is a nucleic acid created?

Answer 5

-adjacent nucleotides that are combined via condensation reactions and phosphodiester bonds

Question 6

how can nucleic acids be broken down in for example digestion?

Answer 6

-they can be broken down by hydrolysis reactions to the nucleotides

Question 7

what is another name for a chain of nucleotides?

Answer 7

-a polynucleotide chain

Question 8

what are the two types of nucleic acids?

Answer 8

-deoxyribose nucleic acids (DNA) and ribose nucleic acids (RNA)

Question 9

what is the general structure of DNA?

Answer 9

-a molecule of DNA consists of two anti parallel strands with the two strands being held together by hydrogen bonds between bases

Question 10

what does the term anti parallel mean?

Answer 10

• it means that the two strand are running in opposite directions

Question 11

what are the 4 bases that DNA contains? how do they bind due to the base pairing rule?

Answer 11

-Adenine that only pairs with Thymine
-Guanine that only binds with Cytosine

Question 12

how many hydrogen bonds are found between the bases in DNA?

Answer 12

-there are 2 hydrogen bonds between A and T
-there are 3 hydrogen bonds between C and G

Question 13

in what shape is the DNA molecule organized in? why is this?

Answer 13

-double helix
-each strand of the DNA is wound round each other like a twisted ladder which are linked together by the bases that follow the base paring rule

Question 14

why is the organization of DNA considered very regular?

Answer 14

-there are 10 base pairs for each complete turn of the helix

Question 15

what is the difference between RNA and DNA?

Answer 15

-RNA molecules are single stranded and are much shorter than DNA
-RNA contain a ribose sugar whereas DNA contain a deoxyribose
-in RNA the base Uracil replaces Thymine and so the bases in RNA are A,U,C and G

Question 16

what are the three types of RNA?

Answer 16

-messenger RNA (mRNA)
-transfer RNA (tRNA)
-ribosomal RNA (rRNA)

Question 17

what is the function of DNA?

Answer 17

-DNA is the genetic code of living organisms
-it regulates the development of living organisms through the control of protein synthesis and the regulation of enzymes

Question 18

what does the sequence of DNA bases determine?

Answer 18

-the amino acid sequence or primary structure of polypeptides

Question 19

what is the definition of a gene?

Answer 19

-a sequence of DNA that codes for a polypeptide

Question 20

what is one of the DNA strands known as?

Answer 20

-a template or coding strand, which functions as the genetic code during semi conservative replication

Question 21

what is the job of mRNA?

Answer 21

-carries the code from the DNA in the nucleus to a ribosome in the cytoplasm where protein synthesis takes place

Question 22

what is the job of tRNA?

Answer 22

-carries the amino acid to the ribosome where protein synthesis takes place
-there are many different types of tRNA as there are many different types of amino acids
-it is a single chain folded into a clover shape

Question 23

what is ribosomal RNA?

Answer 23

-it is made in the nucleolus and forms over half the mass of each ribosome

Question 24

what is DNA replication and when does it take place?

Answer 24

-DNA replication is the process that replicates the DNA molecule and it takes place before the chromosomes duplicate during the process of mitosis and meiosis

Question 25

what is the process of semi conservative repliaction?

Answer 25

-enzyme DNA helicase unzips the two strand of DNA by breaking the hydrogen bonds between bases
-each of the original strands are now known as template strands
-free nucleotides are linked to template strands following the base pairing rule
-the nucleotides of each strand are joined together by the enzyme DNA polymerase which formed phosphodiester bonds between the phosphate and deoxyribose sugar

Question 26

why is the replication of DNA known as semi conservative?

Answer 26

-each of the new DNA molecules contains one original strands and one new strand

Question 27

when was the structure of DNA discovered and who discovered it?

Answer 27

-it was only discovered in the middle of the last century and people called Watson and Crick discovered it

Question 28

what was the two models proposed by Watson and Crick to explain DNA replication?

Answer 28

-the conservative model which proposed that the parental DNA remained intact but copied to the new DNA molecule
-the semi conservative is the the one we just discussed

Question 29

what was the name of the two who proved the semi conservative replication to be true? what year did they discover this?

Answer 29

-Meselson and Stahl in 1958

Question 30

what was did their experiment consist of to prove the semi conservative theory?

Answer 30

-they cultured a type of bacterium using the heavy isotope of nitrogen, N 15
-the N15 was incorporated into the bases of the DNA in the bacteria and over time, the older bacteria died and were replaced
-all the bacteria was transferred to a medium containing the lighter N14 isotope
-following this transfer the bacteria DNA was analyzed and tested at intervals

Question 31

what are the 4 key stages of Meselson and Stahls experiment?

Answer 31

-bacteria containing N14 collected and transferred into a solution containing N15 (1st check)
-bacteria growing in N15 many generations after the transfer from N14(2nd check)
-one generation after the transfer back to a solution with N14 (3rd check)
-two generations after the transfer to N14 (4th check)

Question 32

what does the term density- gradient centrifugation mean?

Answer 32

-it is a technique used to separate the bacterial DNA following sampling at the different stages

Question 33

what was the result of the two different isotopes on the density gradient centrifugation?

Answer 33

-the DNA that contained the lighter N14 was found near the top of the centrifuge tube
-the DNA tat contained the heavier N15 was found near the bottom

Question 34

what did the Meselson and Stahl experiment show after one generation of the bacteria?

Answer 34

-the intermediate position in the tube which means that all the DNA was found as a band around the middle of the tube
-this is because all the DNA contained one strand that had bases containing the N14 and one strand containing the bases from the N15

Question 35

what did the Meselson and Stahl experiment show after the second generation of bacteria DNA?

Answer 35

-there was a ring around the center of the tube and one near the top of the tube
-this means that about half the DNA contained mixed DNA of both N14 and N15 but the other contained only the N14

Question 36

what is the general explanation of the Meselson and Stahl experiment and why does it prove that DNA replicates by semi conservative replication ?

Answer 36

-after one generation the new generation of bacteria had DNA that contained one parental template strand and one new strand which was formed by the N14 medium that the parental bacteria had been transferred to prior to this
-the second generation, each strand from the mixed DNA of the first generation acted as a template to produce bacteria, half pf which contained mixed DNA and the other half contained DNA from only the N14

Question 37

what would you expect to happen during a third generation of the bacteria DNA ?

Answer 37

-it would have the same pattern as the second generation
-but there would be fewer bacteria that contain the mixed DNA and much more containing the lighter DNA
-meaning the lighter band zone at the top would get denser at the top of the centrifuge and the mixed band at the middle would get lighter