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genetics DNA
exam 2
| Question | Answer |
|---|---|
| euchromatin | not tightly coiled, less condensed regions of chromosomes that are transcriptionally active |
| heterochromatin | condensed, tightly compacted regions of chromosomes that are transcriptionally inactive |
| DNA damage | change in DNA structure caused by a damaging agent |
| Variant | change in DNA sequence that comes from the resolution of DNA damage |
| DNA damage can be resolved without... | variant |
| Increase in DNA damage= | increase in amounts of variant |
| What does transcription produce? | an RNA copy of a gene |
| What does mRNA contain? | information to make a polypeptide |
| What does DNA not directly participate in? | translation |
| Does DNA leave the nucleus? | no |
| Where does DNA replication occur? | in the nucleus where it is transcribed to mRNA and then carried to the cytoplasm to be translated to a polypeptide |
| Why can DNA replicate rapidly? | multiple origins of replication, bidirectional replication, highly efficient enzymes (DNA polymerase), helicase |
| Characteristics of the genetic code | unambiguous, degenerate, universal, non-overlapping |
| unambiguous | each codon specifies only one amino acid |
| degenerate | 3rd nucleotide in a codon is in the 'wobble' position, most amino acids are coded for by more than one codon |
| universal | the same codon specifies the same amino acids in almost all living organisms |
| non-overlapping | each nucleotide in an mRNA sequence is read only once, as part of a single codon |
| start codon | AUG-met |
| What does the start codon do? | sets the reading frame for all remaining codons |
| Which base is susceptible to oxidative stress? | Guanine |
| What do germ line variants occur in? | gametes |
| Are germ line variants inherited? | yes |
| cells affected by germ line variants | all cells affected |
| What do somatic variants occur in? | somatic cells |
| Are somatic variants inherited? | no |
| What do somatic variants often lead to? | altered cell function and cancer |
| cells affected by somatic variants | patch affected |
| variant | alterations in DNA sequence that may or may not alter the phenotype |
| How can a variant occur? | spontaneously or be induced |
| How can induced variants occur? | due to exposure to mutagens (ex. radiation) |
| What are common causes of spontaneous variants? | depurination and deamination |
| frameshift variants | result from insertions or deletions of nucleotide which causes shift in reading frame |
| silent variant | codes for same amino acid |
| missense variant | codes for different amino acid |
| nonsense variant | codes for stop codon |
| replication | semiconservative, occurs in multiple origins of replication along the strand |
| three stages of transcription | initiation, elongation, termination |
| transcription: initiation | occurs when the DNA strands begin to separate, and exposes a single-stranded DNA template that will be transcribed into mRNA |
| transcription: elongation | RNA polymerase synthesizes a new RNA strand by adding ribonucleotides complementary to the DNA template strand |
| What happens after a short RNA sequence has been transcribed? | RNA polymerase leaves the promoter and enters into the elongation stage |
| What does elongation continue into? | termination |
| Where are termination DNA sequences? | in the 3' UTR |
| transcription: termination | RNA synthesis stops, and the new RNA molecule is released from the DNA template. |
| TATA box | short DNA sequence found in the promoter region of many eukaryotic genes, key role in initiating transcription |
| What are TATA boxes made up of? | adenine and thymine |
| Where are promoter regions located? | in the 5' untranslated regions of genes |
| What do promoter regions signal? | the initiation of transcription |
| Where are promoter regions located in comparison to the genes they regulate? | immediately adjacent |
| What do promoter regions specify? | where transcription begins and the direction of transcription along the DNA |
| What does the core promoter region include? | includes TATA box, TSS, and cis acting element |
| Where is the proximal promoter region located? | further upstream, in the 5' UTR |
| What does the proximal promoter region influence? | the level of basal transcription |
| What happens at the core promoter region? | determines where RNA polymerase starts and how efficiently transcription begins |
| What happens at the proximal promoter region? | helps regulate the efficiency and rate of transcription initiation, determines how much mRNA is produced |
| What happens if methylation occurs in the promoter region? | it could shut the whole gene down |
| regulatory elements | short DNA sequences that affect the ability of RNA polymerase to recognize the promoter |
| cis-acting elements | DNA sequences that are located in and around eukaryotic genes to which regulatory proteins bind |
| Why is stabilization of the pre mRNA important? | for safe travels out of the nucleus and into the cytoplasm |
| What is important for stabilization of the pre mRNA? | methyl cap on 5', poly A tail on 3' end, splicing |
| Is the methyl cap transcribed? | no |
| Function of the poly A tail | stabilizes pre-mRNA by protecting it from degradation and helping it interact with stabilizing proteins |
| How is the poly A tail formed? | ribonuclease cleaves the 3' end of the sequence AAUAAA before transcriptional terminated, another enzyme adds 100-200 ribonucleotides containing adenine to the 3' end |
| splicing | removing introns and linking exons together with phosphodiester bonds |
| introns | non-coding regions of sequence, removed |
| exons | linked together to form protein-coding sequence |
| What does excising require? | spliceosomes |
| spliceosomes | large complexes composed of smaller nuclear riboproteins, and include small nuclear RNA |
| What do spliceosomes bind to? | an intron |
| What do spliceosomes precisely recognize? | intron/exon boundaries holding mRNA in correct configuration |
| How are introns removed? | through enzymatic reactions |
| How are exons linked? | covalently |
| What does alternative splicing increase? | the number of proteins that can be made from a single mRNA transcript |
| What does alternative splicing do? | makes protein production more efficient |
| proteome | number of proteins an organism can make |
| Where does translation occur? | in the cytoplasm on ribosomes, each with 2 subunits composed of RNA and protein |
| translation | polymerization of amino acids into a polypeptide chain |
| three stages of translation | initiation, elongation, termination |
| What does initiation in translation require? | proteins called initiation factors |
| What happens in initiation during translation? | tRNA complementary anticodon loop binds mRNA, large subunit joins tRNA at the P site |
| What does elongation in translation require? | elongation factors |
| What happens in elongation in translation? | new tRNAs enter the A site and a peptide bond is formed between the first 2 amino acids, ribosomes move in a 5' to 3' directionality along the mRNA, uncharged tRNA moves to the E site and the complex shifts |
| When does termination occur? | When a stop codon is in the a site |
| What happens in termination in translation? | release factors bind to stop codon and the ribosomal subunits, mRNA, and the polypeptide disassociate |
| What is the tRNA? | molecule that matches a triplet codon with the correct amino acid |
| What is tRNA transcribed by? | RNA polymerase III |
| charged tRNA | have an amino acid covalently bound to the 3' end |
| How are charged tRNAs named? | according to the amino acid they carry |
| What does binding between the codon and anticodon of a charged tRNA direct? | the incorporation of amino acids into a growing polypeptide chain |
| What must happen before translation can begin? | the tRNA molecules must be chemically linked to their respective amino acids (charging) |
| Three ribosomal sites | exit (e) site, peptidyl (p) site, aminoacyl (a) site |
| What does each tRNA have? | an additional anticodon complementary and antiparallel to a codon in mRNA |
| What does charging occur under direction of? | enzymes called aminoacyl tRNA synthesis |
| What does each aminoacyl tRNA synthetase recognize? | one amino acid and the structural features of its corresponding tRNA, including its anticodon |
| What does base pairing between an mRNA codon and a tRNA anticodon determine? | which amino acid is added to a growing polypeptide |
| What can misfolded proteins lead to? | diseases, such as alzheimers |
| How can misfolded proteins cause diseases such as alzheimers? | by forming beta sheets which form plaques |
| What do ubiquitins do? | tag misfolded proteins |
| Where do protein ubiquitin complexes move to? | proteasomes, where proteins are degraded by proteases |
| chaperone proteins | correct folding mechanisms, but do not become part of the final protein (recycled) |
| What percent of DNA actually builds proteins? | 2% |
| What type of disorder is XP? | rare, autosomal recessive |
| What does XP predispose individuals to? | skin cancer and sometimes neurological disorders |
| What causes XP? | variants in at least 8 genes involved in nucleotide excision repair, multiple errors in replication |
| What is thymine dimer cause by? | thymine dimer |
| thymine dimer | adjacent thymine bases become cross linked |
| What do thymine dimers interfere with? | transcription and translation |
Created by:
camrynfoster