Term
| What are the components of a DNA nucleotide? |
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Definition
| Adenine, Guanine, Thymine, Cytosine |
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Term
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Definition
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Term
| What are the pyrimidines? |
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Definition
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Term
| What is the ratio of amino acids to nucleotides in a strand of DNA? |
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Definition
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Term
| Distinguish between unique/single copy genes and highly repetitive sequences in nuclear DNA. |
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Definition
| Single copy genes have coding functions and are located specifically in the chromosome whereas highly repetitive sequences, according to the current theory, have no coding function, and are transposable among eukaryotes. |
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Term
| Distinguish between exons & introns. Which type of cells contain only exons? What type of cells contain both introns & exons? |
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Definition
Exons - coding fragments.
Introns - non-coding fragments.
(in genes)
Eukaryotic cells contain both introns and exons whereas prokaryotes only contain exons. |
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Term
| Explain the conservative model. |
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Definition
| After DNA replication, the original DNA strands bond back together. The original strand is conserved. |
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Term
| Explain the dispersive model. |
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Definition
| The new DNA strand has a mixture of old and new DNA. The new strand has new & old DNA dispersed throughout. |
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Term
| Explain the semiconservative model. |
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Definition
| After DNA replication, one strand is "old" and the other one is "new". The new strand was made from the old strand. Half of the DNA strand is conserved. |
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Term
| Which theory of replication is currently accepted? |
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Definition
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Term
| Distinguish between RNA and DNA. Include # of strands, type of sugars, and base pairs. |
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Definition
| RNA is singled-stranded, contains ribose, and has base pairs: Adenine-Uracil, Cytosine-Guanine. DNA is double-stranded, contains deoxyribose, and has base pairs: Adenine-Thymine, Cytosine-Guanine. |
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Term
| Explain the process of DNA replication. |
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Definition
| DNA double helix is unwound and separated into strands by helicase breaking the hydrogen bonds holding the strands together and creating a replication bubble. The single strands are a template for new strands. Primase places RNA primes on the new strand, allowing Polymerase III to add to the strand in a 5’ to 3’ direction. Several small strands are made within the replication bubbled formed by helicase (AKA Okazaki fragments). Polymerase III is removed, replaced with corresponding base pairs using Polymerase I. Ligase binds new base pairs on the lagging strand to the rest of the strand. Bases from hydrogen binds with bases of the parent strand. Nucleotides connect to form new strand. The daughter DNA molecules each rewind into a double helix. |
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Term
| Explain the process of transcription. |
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Definition
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Term
| How does the structure of tRNA allow recognition by a tRNA-activating enzyme that binds to specific amino acid to tRNA? |
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Definition
| Each amino acid has a specific tRNA-activating enzyme that help to tRNA to combine with its complimentary mRNA codon. The enzyme has a 3-part active site that recognizes three things: a specific amino acid, ATP, and a specific tRNA. The enzyme attaches the amino acid to the 3' end of the tRNA. The amino acid attachment site is always the base triple CCA. Each tRNA molecule can attach to one specific amino acid, but an amino acid can have a few tRNA molecules with which it can combine. |
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Term
| Explain initiation. (within translation) |
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Definition
| Once the RNA reaches the cytoplasm, it attaches its 5' end to the small subunit of the ribosome. AUG is called the start codon because it initiates the translation process. The anticodon on one end of a tRNA molecule is complimentary to a specific codon on the mRNA, meaning that the anitcodon and the codon bond by hydrogen bonds. The codon AUG hydrogen bonds with a tRNA molecule holding the amino acid methionine (the initiator tRNA). The large ribosomal subunit has two tRNA binding sites: the P site and the A site. tRNA molecules in these sites attach to the mRNA "conveyor belt". tRNA molecules move from the A site to the P site (because the mRNA moves that way), so when initiation is done the initiator tRNA is in the P site. |
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Term
| Explain elongation. (within translation) |
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Definition
| Another tRNA (tRNA "X") carrying a specific amino acid attaches itself to the next codon at the A site of the larger subunit. These two amino acids (methionine and the amino acid on X) now make a peptide bond with each other. The initiator tRNA breaks off and tRNA X moves from the A site to the P site. Then another tRNA molecule (tRNA "Y") attaches to the codon in the A site. The amino acid that is attached to tRNA Y makes a peptide bond with the amino acid from tRNA X. The codon keeps moving through the ribosome in a 5' to 3' direction (from A to P). This makes the A site vacant for another tRNA to attach a new amino acid. |
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Term
| Explain termination. (within translation) |
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Definition
| Termination: The stop codon is one that does not code for an amino acid and that terminates the translation process. The polypeptide is released and the mRNA fragments return to the nucleus. These nucleotides are recycled and used for RNA and DNA synthesis. tRNA also is returned to its free state and attaches to its specific amino acid so as to be ready for the translation process when needed. |
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Term
| What is the purpose of free ribosomes? |
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Definition
| Free ribosomes synthesize proteins for use primarily within the cell. |
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Term
| What is the purpose of bound ribosomes? |
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Definition
| Synthesize proteins primarily for secretion or for lysosomes. |
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Term
| Outline the significance of complementary base-pairing. |
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Definition
| Because the nitrogenous bases that compose DNA can only pair with complementary bases, any two linked strands of DNA are complementary. This ensures that the old base sequence is conserved. |
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Term
| Explain how a DNA double helix is formed using complimentary base pairing and hydrogen bonds. |
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Definition
| DNA molecules consist of two strands of nucleotides which are then wound together to form a double helix. These are formed between the bases of two strands. However, it is formed by complementary base pairing because Adenine only forms hydrogen bonds with Thymine and Cytosine only forms hydrogen bonds with Guanine. |
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Term
| Describe the genetic code in terms of codons composed of triplets of bases. |
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Definition
| The genetic code is a triplet code- three bases code for one amino acid. A group of three bases is called a codon. |
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Term
| What direction does translation occur in? |
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Definition
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Term
| Distinguish between the sense and antisense strands of DNA. |
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Definition
| The sense strand is the coding strand and has the same base sequence as the mRNA (with uracil instead of thymine). The antisense strand is transcribed and has the same base sequence as tRNA. |
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Term
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Definition
| the synthesis of a strand RNA using a strand of the DNA as a template. An enzyme (RNA polymerase) moves along the DNA strand, temporarily unwinding the double strands. Nucleotides attach to the template strand and elongate the forming RNA strand. The building RNA strand is separated from the DNA as the enzyme moves along the DNA, and the DNA rewinds. RNA differs from DNA in composition, where all instances of thymine are replaced by uracil. |
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Term
| Where is replication initiated in eukaryotic cells? |
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Definition
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Term
| What does the central dogma state? |
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Definition
| Information passes from genes on the DNA to an RNA copy. The RNA copy then directs production of proteins at the ribosome by controlling the sequence of amino acids. |
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Term
| Compare transcription and replication. |
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Definition
| Both require the double helix to be opened to expose the base sequence of the nucleotides; however, replication uses helicase whereas transcription uses RNA polymerase to separate these two DNA strands. |
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Term
| What is the promoter region? |
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Definition
| A short sequence of bases that is not transcribed. |
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Term
| What does the "A site" do in the ribosome? |
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Definition
| holds the tRNA carrying the next amino acid to be added to the polypeptide. |
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Term
| What does the "P site" do in the ribosome? |
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Definition
| holds the tRNA carrying the growing polypeptide chain. |
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Term
| What does the "E site" do in the ribosome? |
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Definition
| site from which tRNA that has lost its amino acid is discharged |
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