Nucleic Acids

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Name the components of an individual nucleotide
A pentose sugar, a phosphate group and a nitrogen-containing organic base
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Name the organic bases
Adenine, Cytosine, Guanine, Thymine and Uracil
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What reaction combines the components of a mononucleotide?
Condensation reaction
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How are two mononucleotides joined?
A condensation reaction between the pentose sugar of one mononucleotide and the phosphate group of another
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What are two mononucleotides joined together called?
Dinucleotide
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What bond links two mononucleotides?
Phosphodiester bond
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What is a polynucleotide?
The linking of nucleotides forming a long chain
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What bases are purines?
Adenine and Guanine
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Purines have a single/double ringed structure
Double
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Which bases are pyrimidines?
Thymine and cytosine
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Pyrimidines have a single/double ringed structure
single
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How many polynucleotide chains make up RNA?
1
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What is the name of the pentose sugar in RNA?
Ribose
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What are the bases of RNA?
Adenine, cytosine, guanine and uracil (no thymine)
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Name the three types of RNA
mRNA, tRNA and rRNA
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Is RNA self-replicating?
No
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What is the pentose sugar in DNA?
Deoxyribose
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How many polynucleotide strands make up DNA?
2
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What holds the 2 strands together?
Hydrogen bonds
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What does adenine pair with in DNA?
Thymine as it is complementary to adenine
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What does cytosine pair with in DNA?
Guanine as it is complementary to cytosine
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What is the structure of DNA called?
Double helix
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What joins the phosphate group to the pentose sugar?
An ester bond
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What joins the pentose sugar to the organic base?
Glycosidic bond
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What is the 5' (5 prime) carbon attached to?
A phosphate group
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What is the 3' attached to?
A hydroxyl group
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Why are DNA strands said to be anti-parallel?
One strands runs 5'-3' while the other runs in the opposite way 3'-5'
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Which enzyme assembles nucleotides?
DNA polymerase
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Why is DNA a stable molecule?
The phosphodiester backbone protects the chemically reactive organic bases inside the double helix
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How many hydrogen bonds are there between cytosine and guanine?
3
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How many hydrogen bonds are there between adenine and thymine?
2
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Why is it that the higher the proportion of C-G base pairings, the more stable the DNA molecule is?
There are more hydrogen bonds between the C-G bases
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What is the function of DNA?
Hereditary material responsible for passing genetic information from cell to cell and generation f=to generation
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Why does DNA provide genetic diversity?
There is an almost infinite variety of base sequences
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How is DNA adapted to its function?
Very stable structure so rarely mutates, the strands can separate easily in DNA replication as they are only joined by hydrogen bonds, large molecule so carries large amount of genetic info, base pairs within the helical cylinder protected
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What does the function of DNA depend on?
The sequence of the base pairs
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Describe the process of semi-conservative DNA replication
DNA helicase separates the 2 strands by breaking the hydrogen bonds linking the base pairs, free nucleotides that have been activated bind to their complementary bases, once bound the free nucleotides are joined by DNA polymerase which makes cont
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cont phosphodiester bonds, the remained unpaired bases continue to attract their complementary bases, finally all the nucleotides are joined to form a complete polynucleotide chain using DNA polymerase, two identical molecules of DNA are formed cont
cont each molecule retains half of the original DNA material
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What are the requirements for semi-conservative DNA replication?
The 4 types of nucleotides must be present with their bases, both strands of the DNA molecule act as a template for the attachment of these nucleotides, the enzyme DNA polymerase, a source of chemical energy to drive the process
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Which 3 facts did Meselsohn and Stahl base their work on?
-all the bases in DNA contain nitrogen- nitrogen has 2 forms (lighter nitrogen 14N and heavier nitrogen 15N)-bacteria will incorporate nitrogen growing medium into any new DNA that they make
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Describe the Meselsohn and Stahl experiment
They cultured bacteria in a 15N medium. 15N is a heavy isotope of nitrogen so the DNA synthesized is of heavy density. They then shifted the bacteria to a 14N medium, DNA was isolated at different times corresponding to replication cycles cont
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cont 0, 1, and 2. After one replication cycle, the DNA was all of intermediate density. This rules out the conservative replication model, which predicts that both heavy density DNA and light density DNA will be present, but none of cont
cont intermediate density will be present. This result is consistent with the semiconservative replication model, which predicts that all DNA molecules will consist of one 15N-labeled DNA strand and one 14N-labeled DNA strand
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What do the results of the Meselsohn and Stahl experiment show?
After two replication cycles, two bands of DNA were seen, one of intermediate density and one of light density. This result is exactly what the semiconservative model predicts: half should be 15N-14N intermediate density DNA and half should be 14N-14
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light density DNA. This result rules out the dispersive replication model, which predicts that after replication cycle 1, the DNA density of all DNA molecules will gradually become lower, so no intermediate density DNA should remain at replication
cycle 1, the DNA density of all DNA molecules will gradually become lower, so no intermediate density DNA should remain at replication cycle 2. The semiconservative model is correct.
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What does mitosis produce?
2 daughter cells that have the same number of chromosomes as the parent cell and each other
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In what case would the nuclei /DNA of the daughter cells not be identical to the parent cell?
A mutation
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What is mitosis preceded by?
Interphase
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What occurs during interphase?
DNA replication. The 2 copes of DNA after replication remain joined by the centromere
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What are the 3 phases of interphase?
The 1st growth phase during which there are checks for if the cell is the right size, not damaged and for nutrients. There is a synthesis phase where DNA replication occurs and the 2nd growth phase where the cell prepares for mitosis (more checks)
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Describe prophase
Chromosomes become visible and shorten/thicken, centrioles move to opposite ends of the cell, spindle fibres develop and span from pole to pole, the nucleolus disappears, the nuclear envelope breaks down leaving the chromosomes free in the cytoplasm
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Describe metaphase
Chromosomes can be seen to be made up of 2 chromatids, microtubules from the poles are attached to the centromere and the chromosomes are pulled along the spindle apparatus, chromosomes arrange themselves across the equator of the cell
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Describe anaphase
Centromeres divide into 2 and the spindle fibres pull the individual chromatids apart, chromatids move rapidly to their respective poles, energy provided by the mitochondria which gather around the spindle fibres
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How can anaphase be prevented?
If the cell is treated with chemicals that destroy the spindle the chromosomes will remain at the equator
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Describe telophase
The chromosomes reach their respective poles, become longer and thinner, then disappear altogther, leave widely spread chromatin, spindle fibres disintegrate, nucleolus and nuclear envelope reform
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What is cytokinesis?
When the cytoplasm divides
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By which process is cell division carried out in prokaryotic cells?
Binary fission
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Describe cell division in a prokaryotic cell
The circular DNA molecule replicates and both copies attach to the cell membrane, plasmids also replicate, cell membrane begins to grow between 2 DNA molecules and then divides the cytoplasm in 2, a new cell wall forms between the 2 molecules of DNA
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Why can viruses not undergo cell division?
Viruses are non-living
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How do viruses replicate?
By attaching to their host cell with attachment proteins on their surface, inject their nucleic acid into the host cell, genetic info in nucleic acid provides 'instructions' for the host cell to start producing and assembling viral components
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Why is it essential to make exact copies of cells?
Growth, repair, reproduction
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What are the 3 stages of the cell cycle?
Interphase, nuclear division and cytokinesis
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What is cancer caused by?
A growth disorder of cells
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What is a tumour?
A group of abnormal cells which develops and constantly expands in size
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When does a tumour become cancerous?
When it changes from benign to malignant
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What causes uncontrolled mitosis?
A mutation in the genes that affect the rate of mitosis
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Describe malignant tumours
Grow rapidly, are less compact and are more likely to be life threatening
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Define benign tumour
Grow slowly, more compact and less likely to be life threatening
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What drugs are usually used to treat cancer?
Chemotherapy
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How does chemotherapy disrupt the cell cycle?
Preventing the DNA from replicating and inhibiting the metaphase stage by interfering with spindle formation
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Are chemotherapy drugs more effective against rapidly dividing cells?
Yes so cancer cells are damaged to a greater extent than normal cells due to their higher rate of division
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Why is hair loss a common side effect of chemotherapy?
Hair-producing cells are rapidly dividing
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Card 2

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Name the organic bases

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Adenine, Cytosine, Guanine, Thymine and Uracil

Card 3

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What reaction combines the components of a mononucleotide?

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Card 4

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How are two mononucleotides joined?

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Card 5

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What are two mononucleotides joined together called?

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