Franklin, Watson, and Crick
Structure
Functions
Rules
Definitions
100
Summarize the major experimental questions and conclusions of Rosalind Franklin, and Watson & Crick
The scientists wanted to find out how many strands DNA had; which directions did the strands run; were they on the inside or outside; and how were the four chemical bases arranged. These questions were answered when Rosalind Franklin discovered the structure of DNA through x-ray crystallization and Watson and Crick’s model was confirmed to be correct. They concluded that DNA has two strands running in opposite directions shaped as a double helix; and that there are four nitrogenous bases - adenine bonded with thymine and cytosine with guanine - on the interior of the helix. These insights were theorized by Watson and Crick, but not endorsed until confirmed by photo 51, and then they assembled the first accurate DNA model.
100
Identify a nucleotide on a DNA diagram
100
Explain why the shape of a DNA molecule is called a double helix
The two polymers of nucleotides are bonded together in two complementary strands which wind/twist together, creating the double helix shape.
100
Leading strand and lagging strand
The leading strand is synthesized at the 3’ end of the strand by adding nucleotides, while the lagging strand is synthesized by adding nucleotides to the 5’ end.
100
Summarize the major differences (in general) in DNA replication between prokaryotes and eukaryotes
In prokaryotic replication, the process is a continuous phase in a circular double stranded DNA molecule, replicating in the cytoplasm. Whereas in eukaryotic replication, the process occurs only in the s phase of the cell cycle in a linear double stranded DNA molecule, replicating in the nucleus.
200
Describe how Rosalind Franklin contributed to the discovery of the structure and function of DNA
Franklin was the only scientist of the researchers with a degree in chemistry, coming to her advantage when introduced to X-ray crystallography. Franklin used this technique to discover the structure of DNA. Prior to this discovery, she had experience in working on the structure of RNA structure. She discovered that by controlling the water content of the DNA specimens, the molecule could exist in two forms, allowing her to capture a photo of the B form, which supported Watson and Crick’s assembly of the DNA model.
200
Identify a Nitrogenous Base, a 5-Carbon sugar, and a phosphate group on a DNA diagram
200
Explain why replication of DNA is necessary with the cells of an organism
DNA replication is necessary because it ensures that daughter cells will each get a copy of the genome, and therefore be successful in inheritance of traits. The process is also essential for cell division to occur during growth and repair; and all genetic information is stored in DNA, which we cannot live without.
200
Explain the significance of Okazaki fragments
Okazaki fragments are the small DNA fragments that form during the discontinuous synthesis of the lagging strand during replication. The fragments allow for both daughter strands to be synthesized, which is necessary for replication to occur.
200
Explain what kind of organic compound DNA is and what the monomer / polymers are of the molecule
DNA is a nucleic acid. The monomer is nucleotides and the polymer is the long strands that wind together, made up of nucleotides.
300
Describe how James Watson contributed to the discovery of the structure and function of DNA
Watson had two degrees in biology, his doctorate giving him interest in genetics. He joined the project after seeing Maurice Wilkins X-ray crystallographic photographs of DNA. Watson provided the data on which the structure was based. He discovered that the four base pairs must be linked in indefinite pairs, and formed a molecular model of DNA with Francis Crick.
300
Explain why the shape of a DNA molecule is called a double helix
The two polymers of nucleotides are bonded together in two complementary strands which wind/twist together, creating the double helix shape.
300
Summarize the overall functions of DNA
DNA codes for proteins by way of genes; a unit of heredity. Proteins are responsible for phenotypes; coding physical characteristics, and enzymes for catalyzing metabolic reactions. To reproduce daughter molecules, DNA goes through replication having helicase break apart hydrogen bonds allowing for the two strands to separate, and for primers to form. Then polymerase fills in any gaps in each new molecule, consisting of one parent strand and one new.
300
Explain why replication is referred to as semi-conservative
Replication is referred to as semi-conservative because one of the strands is conserved from the parent DNA, while the other strand is newly synthesized. This process uses less energy.
300
Determine a complementary strand of DNA if you are given one strand of the molecule
A complementary strand of DNA runs in the opposite direction of the given strand, and would be 3’ rather than 5’. If the sequence of the given strand goes CAAGTTCAAGTTC, then the complementary strand would have the sequence CTTGAACTTGAAC.
400
Describe how Francis Crick contributed to the discovery of the structure and function of DNA
Crick earned his degree in physics, and was found by Watson to be his colleague on the DNA project. Inspired by Max Perutz’s work on hemoglobin and succession of molecular models, Crick agreed. Watson and Crick used Franklin photos (without her permission) as a template for their DNA models,
400
Describe and identify the overall structure and the individual structural components of a DNA molecule
DNA is a unit of heredity functioning as chemical storage of genetic information made up of chromosomes. The double helix structure allows for the two strands to run in opposite directions being complementary, and the hydrogen bonds be easily broken to allow the molecule to replicate. A DNA molecule consists of the polymer nucleotides; which is made up of 5C deoxyribose sugars, a phosphate group, and a nitrogenous base; all connected by covalent bonds. Two nucleotides are bonded by hydrogen bonds, and the strands are complementary.
400
Explain why the structure of DNA is referred to as antiparallel (explain 3’ and 5’)
DNA structure is referred to as antiparallel as the complementary strands run in opposite directions, one end being 3’ and the other 5’ and opposite for the other strand. 5’ and 3’ refer to the carbon numbers in the molecule's sugar backbone. The 5’ (five prime) carbon has a phosphate group attached, and the 3’ (three prime) carbon has a hydroxyl group attached.
400
Explain Chargaff’s rules and calculate amounts of base expected if given data
Chargaff's rules state that within any organism, the amount of adenine is equal to the amount of thymine, and the amount of guanine is equal to the amount of cytosine. The organism cavia porcellus (guinea pig) has 30% guanine, so therefore 30% cytosine, 20% adenine, and 20% thymine. The amount of purine is equal to the amount of pyrimidine.
400
Identify what type of bonds hold together the N-Bases in the DNA molecule, and describe whether this is an inter- or intra- molecular force
The nitrogenous bases are held together by the intermolecular force hydrogen bonds. It is an intermolecular force because of the attractive or repulsive forces that exist between two molecules, and are very weak. This allows for the bonds to easily be broken by helicase during replication so the strands can separate to create daughter molecules.
500
Explain the significance of Photo 51
Photo 51 showed the molecule's double-helix structure of deoxyribonucleic acid and its contents of genetic instructions for the organism's development. The photo taken by Rosalin Franklin through X-ray crystallization was used to confirm Watson and Cricks hypothesis, allowing them to assemble the first correct DNA model. This photo introduced DNA to the world, allowing scientists to make further discoveries in the world of genetics.
500
Explain why the structure of DNA is referred to as antiparallel (explain 3’ and 5’)
DNA structure is referred to as antiparallel as the complementary strands run in opposite directions, one end being 3’ and the other 5’ and opposite for the other strand. 5’ and 3’ refer to the carbon numbers in the molecule's sugar backbone. The 5’ (five prime) carbon has a phosphate group attached, and the 3’ (three prime) carbon has a hydroxyl group attached.
500
Explain what is meant by directional synthesis (identify which end of a nucleotide the DNA polymerase enzyme can attach to)
Directional synthesis refers to how DNA is always synthesized in the 5’ to 3’ direction. This means that polymerase can add nucleotides to the 3’ end of the strand only.
500
Summarize the process of replication and explain the results
Replication starts by the two complementary strands being unwound by the enzyme helicase, separating the strands at specific sites. The parent strands structural pattern is used as a template for the sequence of bases. The bases on the parent strand are bonded to each other as a new strand, allowing for each new molecule of DNA to be half parent and half new; also known as semi-conservative.
500
Identify the major enzymes involved in the replication process and how they work
Helicase - Helicase separates the two DNA strands into single strands which allows them to be copied. The enzymes do this by breaking apart the hydrogen bonds holding together the nitrogenous bases, unwinding the molecule.
Polymerase - Polymerase reads the nucleotides along the single strand template of DNA, inserting new complementary nucleotides into the primer to make the sequences complementary to one another.
Ligase - Ligase joins together fragments of the newly synthesized DNA, filling in the gaps, forming a seamless strand.