What two factors contribute to the stabilization of complementary base pairs between A&T and
G&C? How are the terms polymorphism and mutation related?
DNA sequence variations are sometimes described as mutations and sometimes as polymorphisms. What is the difference between these terms and how are they applied to the human genome? A mutation is defined as any change in a DNA sequence away from normal. This implies there is a normal allele that is prevalent in the population and that the mutation changes this to a rare and abnormal variant. In contrast, a polymorphism is a DNA sequence variation that is common in the population. In this case no single allele is regarded as the standard sequence. Instead there are two or more equally acceptable alternatives. The arbitrary cut-off point between a mutation and a polymorphism is 1 per cent. That is, to be classed as a polymorphism, the least common allele must have a frequency of 1per cent or more in the population. If the frequency is lower that this, the allele is regarded as a mutation. Why are some sequence variants more common than others? Sequence variants that directly and overtly cause human diseases are generally rare in the population because they reduce fitness. Such disease alleles are classed as mutations. However, not all mutations cause diseases. Any new sequence variant, even if neutral or beneficial in effect, will start off as a rare mutation. Polymorphic sequence variants usually do not cause overt debilitating diseases. Many are found outside of genes and are completely neutral in effect. Others may be found within genes, but may influence characteristics such as height and hair colour rather than characteristics of medical importance. However, polymorphic sequence variation does contribute to disease susceptibility and can also influence drug responses (Single Nucleotide Polymorphisms). SNPs occur about once every 1000 base pairs in the genome, making up the bulk of the 3 million variations found in the genome. Unlike the other, rarer kinds of variations, many SNPs occur in genes and in the surrounding regions of the genome that control their expression. The effect of a single SNP on a gene may not be large - perhaps influencing the activity of the encoded protein in a subtle way - but even subtle effects can influence susceptibility to common diseases, such as heart disease or Alzheimer's disease. The above definitions cannot be applied rigorously. A rare disease allele in one population can become a polymorphism in another if it confers an advantage and increases in frequency. A good example is the allele of sicklecell disease. In Caucasian populations this is a rare sequence variant of the betaglobin gene that causes a severely debilitating blood disorder. In certain parts of Africa, however, the same allele is polymorphic because it confers resistance to the blood-borne parasite that causes malaria.
What two factors contribute to the stabilization of complementary base pairs between A&T and G&C? How...
A double-stranded DNA molecule of 175 base pairs long had (A+T/(G+C) = 0.75. How many adenine nucleotides are there in this DNA? 75 37.5 150
2) Draw the two base-pairs, A-T and G-C, depicting the nitrogen-containing bases attached to the deoxyribose-phosphate backbone of DNA. Include the hydrogen bonding sites. (Hint: Look at Figure 12.7, Chemistry in Context 7h Edition). A-T base-pairing (show the Hydrogen bonding): G-C base-pairing (show the Hydrogen bonding): 101 Oy. The process CH3 thymine 0----H-N HC adenine N- To deoxyribose and DNA chain To deoxyribose and DNA chain N -H cytosine HC-C guanine HC N To deoxyribose and DNA chain To deoxyribose...
Below are bases used in nucleic acids. (a) why are they called bases-what allows them to act as a base? (b) the two strands of DNA are held together in the double helix form by hydrogen bonds between complementary base pairs. What is a hydrogen bond? (c) Suppose a new disease appears that creates covalent, rather than hydrogen, bonds between the two strands of DNA (this is VERY unlikely!). If you had to design a drug to combat the disease,...
How many hydrogen bonds exist between this DNA strand and its complementary strand? 5'-AGGCCTT-3 Number As a result of rotation about six of its bonds, DNA can exist in a variety of forms. Determine whether each of the following images and properties describes the A form, B form, or Z form of DNA. A form B form Z form All antiparallel strands left-handed C-3' of deoxyribose 18.4 A is out of the plane of helix diameter the other ring atoms...
1. Answer the following questions concerning a section of double-stranded DNA containing 1000 base pairs. a. If the DNA contains 28% adenosine residues, how many guanosine residues are in the DNA? b. Are the nucleotide compositions of each of the two individual strands of DNA identical? Explain. c. If the DNA is entirely in the B-DNA conformation: i. How many helical turns does the DNA contain? ii. What is the length of the DNA? 2. Write the sequence of a...
How DNA Is Copied 4. What does it mean that the two strands of DNA are complementary? 5. What is DNA replication?, 6. Using your notes, book, and this assignment, place the steps of DNA replication in the correct order. a. The enzyme DNA polymerase moves along the exposed strands and adds complementary nucleotides to each nucleotide in each existing strand. b. The DNA double helix breaks or unzips down the middle between the base pairs. C. A complementary strand...
What type of DNA mutation is this? Original strand: A-T-C-G-T-A-G-G-C-T-A-G Mutated strand: A-T-C-G-A-T-A-G-G-C-T-A-G nucleotide deletion nucleotide insertion O single nucleotide substitution (point mutation) O trinucleotide repeat
Biochemistry homework 4. Explain why A-T and G-C are the only base pairs possible in normal double stranded DNA? 5. Match the appropriate characteristics in the right column with the structures of double strand or single strand DNA. (A) double-strand DNA: (B) single-strand DNA: (i) is a rigid rod (ii) shows a greater hyperchromic effect. (iii) contains equal amount of A and T bases. (iv) may contain different amounts of C and G bases. (v) contains U rather than T...
The C is located between the two Gs A T C T T G "C" G 3. The following is a DNA coding strand sequence encoding the C-terminus of a protein: 5"...A TCTTG GTTGACAACAGTT G A...3"
Genetic Code: The dictionary of the language of life Use the Genetic Code as a "dictionary" to solve the exercises on next page 5. If a mutation happens in the DNA that changes the T at base 14 to a G: a) What would be mutated sequence of nucleotides in the corresponding codon in the mRNA and the anticodon in the tRNA? Is there any change in the corresponding amino acid in the protein? b) What is the name of this type of...