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Nucleic Acids

Genetics, Variation and Selection

QuestionAnswer
What are the basic units of nucleic acids called? Nucleotides
Name the two main nucleic acids. DNA (deoxyribonucleic acid) and RNA (ribonucleic acid)
State the three basic components of nucleic acids. 1) A pentose sugar (ribose or deoxyribose) 2) A phosphate group 3) A nitrogenous base (A, G, C, T or U)
Name the 3 pyrimidine(single ring) bases cytosine, thymine and uracil
Name the 2 purine (double ring) bases. adenine and guanine
Name the covalent bond which occurs during the condensation reaction which forms polynucleotides. phosphodiester bond
List the three types of RNA ribosomal rRNA, transfer tRNA and messenger mRNA
State the function of rRNA Formation of ribosomes
State the function of tRNA Lines up amino acids on the mRNA template during protein synthesis.
State the function of mRNA Copies the instructions from the DNA in the nucleus and brings it to the cytoplasm where translation and protein synthesis occurs.
T or F. DNA is a sequence of nucleotides whereas proteins are a sequence of amino acids. T
A polymer of nucleotides is called a polynucleotide
A polymer of amino acids is called a polypeptide
Describe three key feature of DNA's structure. 1) It is made up of 2 nucleotide polymer stands 2) The strands are anti-parralel and are wound together by hydrogen bonds to form a double helix 3) The pentose sugar is deoxyribose.
T or F. Purine bases are always paired with pyrimidine bases via hydrogen bonds between nucleotide chains. T
Adenine(A) always pairs with Thymine(T) with 2 hydrogen bonds
Guanine (G) always pairs with Cytosine(C ) with 3 hydrogen bonds
In the absence of thymine (e.g. in RNA) , adenine pairs with Uracil (U)
RNA has a single polynucleotide strand (chain) while DNA has a double polynucleotide chain (double helix)
RNA has the pentose sugar ribose while DNA has the pentose sugar deoxyribose
The organic bases of RNA are adenine, guanine, cytosine and uracil while in DNA the organic bases are adenine, guanine, cytosine and thymine
RNA is manufactured in the nucleus but found throughout the cell while DNA is found mostly in the nucleus with some present in mitochondria and chloroplasts
RNA is chemically less stable while DNA is chemically very stable
Why is DNA replication considered semi-conservative? Each new DNA molecule contains one of the original DNA strands and one newly synthesized strand.
Step 1 of DNA replication is the opening up of the DNA double helix. Describe the process. The enzyme helicase breaks the hydrogen bonds between the two parental strands of DNA at different points forming replication forks.
Step 2 of DNA replication is the unwinding of DNA. Describe this process. DNA is separated as it unwinds. Topoisomerase enzyme aids this process.
Step 3 of DNA replication is the assembling of the leading strand. Describe this process. One strand of DNA is made by the enzyme DNA polymerase in a continuous process that occurs in the same direction (5' -> 3') as the replication fork is moving. Free nucleotides form complementary base pairs with the strand.
Step 4 of DNA replication is the assembling of the lagging strand. Describe this process. The antiparallel strand of DNA runs in the 3' -> 5' direction which is opposite to the direction in which DNA polymerase works. Therefore short sections of complementary DNA are made simultaneously in the 5' -> 3' direction and linked by enzyme ligase.
Step 5 of the DNA replication process is the removal of wrongly coded DNA. Describe this process. DNA polymerase checks and corrects most errors which may occur in the assembling of the new DNA strand. This is important to prevent to wrong amino acid being coded for and a different primary structure of protein.
What is a gene? A sequence of nucleotides on a DNA molecule that code for a polypeptide or a functional RNA.
What is a codon? A sequence of three adjacent nucleotides (bases) in mRNA which code for an amino acid.
What is the genetic code? Sequences of three bases (A, T, C and G) in DNA that code for the 20 amino acids in proteins; groups of three bases are called triplets in DNA and codons in mRNA.
How many possible combinations are possible for a triplet of bases where there are only four bases? 4 raised to the 3rd power = 64
T or F. The codon is always read in the 5' to 3' direction. T
The genetic code is degenerate. What does this mean? Most amino acids are coded for by more than one triplet.
State the codon which always STARTS a sequence and codes for methionine. AUG
State the three codons which STOP a sequence and do not code for any particular amino acid. UAA, UAG and UGA
The genetic code non-overlapping. What does this mean? Each base is read only once Eg. 123456 is read as 123 456 instead of 123 234 etc
The genetic code is universal. What does this mean? Each triplet codes for the same amino acid in all organisms with a few minor exceptions.
Name the two main processes involved in protein synthesis. Transcription and Translation
T or F. Each cell is capable of making any and every protein from just 20 amino acids but what is manufactured depends on the instructions that are provided. T
What is transcription? The process of making mRNA using one strand of the section of DNA as a template. This mRNA then carries the information out of the nucleus to the ribosomes in the cytoplasm where translation takes place.
Why is transcription necessary? DNA cannot leave the nucleus as it is too large to pass through the nuclear pores. mRNA transcripts are made in transcription which copies the DNA and travels to the ribosomes in the cytoplasm for protein synthesis.
Outline step 1 of transcription. Helicase enzyme breaks hydrogen bonds between base pairs of DNA strands at specific regions. The strands separate and expose their nucleotide bases in that region.
Outline step 2 of transcription. Free complementary RNA nucleotides pair with the template strand of DNA. Enzyme RNA polymerase then moves along and join these free nucleotides together.
Outline step 3 of transcription. As the RNA polymerase adds the nucleotides one at a time, to build a strand of pre-mRNA, the DNA strands rejoin behind it. As a result, only around 12 base pairs on the DNA are exposed at any one time.
Outline step 4 of transcription. RNA polymerase continues until it recognizes a 'stop' signal. The pre-mRNA is then processed within the nucleus to form the final mRNA molecule. This mRNA leaves the nucleus via a nuclear pore.
T or F. There is no thymine in any RNA molecule. It is uracil that pairs with adenine in RNA. T
What is an intron? A portion of a gene that does not code for amino acids and is often removed from the pre-mRNA before the final mRNA leaves the nucleus.
What is an exon? The portion of a gene that codes for amino acids.
What is translation? The process by which the sequence of bases along the length of the mRNA is used to produce the sequence of amino acids in a polypeptide.
What is an anticodon? Group of three bases on tRNA that pairs with codon on messenger RNA during translation.
What is amino acid activation? The attachment of amino acids to specific tRNA molecules.
Ribosomes have an A and a P site. What does these do? A (aminoacyl) site accepts the tRNA-amino acid complex. P (peptidyl) site holds the lengthening polypeptide.
Outline step 1 in translation. A tRNA-methionine complex enters the A site of the ribosome.
Outline step 2 in translation. The ribosome moves the complex to the P site and exposes the A site for another tRNA molecule carrying the complementary anticodon. This continues until the ribosome reaches a stop codon.
Outline step 3 in translation. The enzyme peptidyl transferase joins together the amino acids delivered by the tRNA to form a growing polypeptide chain.
What is the relationship between the sequence of nucleotides and the amino acid sequence in a polypeptide? A triplet of nucleotide bases on mRNA are complementary to the anticodon carried by a tRNA molecule which carries a specific amino acid.
What is the relationship between the structure of DNA, protein and phenotype of an organism? DNA codes for the sequence of amino acids which form the primary structure of a protein. After translation, the polypeptide folds to form higher levels of organization. Proteins significantly impact the organisms' phenotypic (observable) expression.
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