DNA and RNA Structure

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  • Created by: Lotto65
  • Created on: 09-01-17 17:46
What does DNA stand for?
Deoxyribonucleic acid
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What does RNA stand for?
Ribonucleic acid
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Who discovered DNA and RNA?
Friedrich Miescher
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When was DNA and RNA discovered?
1896
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Why are they called nucleic acids?
They were discovered in material extracted from the nuclei of cells
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What was the Hammerling Acetabularia experiment?
Got two different species of Acetabularia algae and put the head on the other one's stem and vice versa. He also removed other specific parts. These parts grew and the stem with characteristics of plant that had its nucleus inserted
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What can we tell from the Hammerling experiment?
Genetic information / characteristics were stored in the nucleus
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What happened in Griffith's experiment?
Got three rats. Injected first with S-pneumococcus and it died as was susceptible; Second rat was injected with r-pneumococcus and lived as was resistant; Third rat injected mixture of heat killed S-pneumococcus and r-pneumococcus but died
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What is the explanation for the Griffiths experiment?
Transformation occurred
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What is transformation?
When the genetic make-up can be changed by the introduction of DNA from the surrounding environment
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What happened in the Oswald Avery experiment?
S-strain had large cellular structures removed; protease enzymes to remove protein; Put S-strain in R-strain so R-strain became S-strain; Remnants of R-strain treated with Deoxyribonuclease to remove DNA so it no longer transformed
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What did we learn in the Oswald Avery experiment when the R-strain became the S-strain?
Proteins do not carry genes causing disease
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What happened in the Hershey and Chase experiment?
Made phage inject DNA into a bacterial cell. Phage had radioactive coat injected normal DNA so made normal phages. Normal coat phage with radioactive DNA made radioactive phage
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How did they make the phage radioactive?
Place them in an S-35 isotope
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What is a nucleotide?
One section of one of the strands that makes up the double helix shape
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What makes up a nucleotide?
A phosphate group, a pentose sugar and a base
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What is the precise name of a base in DNA?
Nitrogenous base
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How is the phosphate group bonded to the pentose sugar?
Covalent bonds / Phosphodiester bonds
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How is the pentose sugar bonded to the base?
Covalent bonds
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How are the bases bonded together?
Hydrogen bonds
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What is a polynucleotide?
One strand of DNA that makes part of the double helix that is composed of many nucleotides
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Name the four bases in DNA
Cytosine, thymine, adenine and guanine
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Why are bases important?
Their sequencing codes the order of nucleotides in the polynucleotide and nucleic acid. So codes the type of nucleotide to determine how information is stored and what information is stored. Codes specific characteristics and proteins
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What is a nucleosome?
A package of DNA
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What makes up a nucleosome?
Eight histones in a central core with DNA coiled round them
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What is a histone?
A protein with a positive charge
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How many of each type of histone is there in a nucleosome?
2
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What is the use of histones?
Histones help to package DNA. Eukaryotes have large genomes so they need to be packaged and supercoiling means a large length of DNA can be packed in a smaller space in the nucleus
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What did Rosalind Franklin discover?
That DNA is helical in shape
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How did Rosalind Franklin make her discovery?
She developed a high resolution camera containing x-ray film. X-ray diffraction on DNA. Rotated three times to see pattern of scattering
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What is x-ray diffraction?
X-rays pass through a material and most pass through but some are scattered by particles of the material
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What did Maurice Wilkins discover?
First image of DNA fibres and DNA 'strands'
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How did Maurice Wilkins make this discovery?
X-ray diffraction of DNA fibres
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What did Linus Pauling discover?
Polypeptide chains can coil into a helix shape known as the alpha helix
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How did Linus Pauling make this discovery?
Working with a sheet of paper, he folded it at sites where he knew the chain could bend. Then X-ray diffraction of fibrous proteins
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What did Erwin Chargaff discover?
Number of thymine residues equals number of adenine residues - same for cytosine and guanine - base pairing
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How did Erwin Chargaff discover this?
Paper chromatography to separate DNA before adding acid to free nucleotides. Then UV spectrophotometry analysed exact amounts of bases in sample
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What is a residue?
The small amount of something that remains after the main part has been removed
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What did James Watson and Francis Crick discover?
The structure of DNA in having a double helix and base pairs inside antiparallel sugar-phosphate strands
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How did Watson and Crick make this discovery?
Built models using knowledge from other scientists. Made bases using cardboard. In second model they used metal rods with a sheet cut to shape and small clamps
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What was the problem with Watson and Crick's first model?
Did not take into account there would not be enough magnesium to form so many cross links and Chargaff's theory not included
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What were the main features of Watson and Crick's first model?
Bases on the outside, triple helix and magnesium ionically bonded strands together at phosphate groups
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Name three differences between DNA and RNA
DNA - Deoxyribose sugar (one less oxygen) , 2 polynucleotides, adenine, guanine, cytosine and thymine RNA - Ribose sugar, One strand, adenine, guanine, cytosine and uracil
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What is the chromosome of prokaryotes made of?
Only DNA
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Why can the strand of DNA bond to histones?
DNA has negative charges in its strand and proteins have positive charges - electromagnetic forces
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What is another word for a nucleosome?
Chromatin
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What is 3' - 5' linkage?
The phosphate heads will bond to carbon 5 of the pentose sugar and then carbon 3
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How do the pentose sugars face on the two strands?
On one strand they will face the right way up starting with carbon 5 and ending with carbon 3. The other way they will be upside down with carbon 3 at the top and carbon 5 at the bottom
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Why are the bases on the inside?
They are hydrophobic
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How many hydrogen bonds does AT form?
2
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How many hydrogen bonds does GC form?
3
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What is the name of the reaction that forms phosphodiester bonds?
Condensation reaction
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Card 4

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Card 5

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