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chp 11 genetics
| Question | Answer | |
|---|---|---|
| Nonhistone chromosomal proteins | either act as STRUCTURAL or PROCESSING (TC (transcription) or replication) proteins. Ex- scaffold proteins, kinetochore, telomere caps, molecular motors to move chromosomes during mitosis/meiosis. | |
| What are histones? | forms of proteins | |
| What are scoffold proteins? | skeleton of chromosome and support it. | |
| SAR’S | scaffold attachment regions where scaffolds attach to. | |
| What is a kinetochore? | proteins that spindle fibers attach to. | |
| Describe a nucleosome | DNA plus the octomere (NO H1). So octomere= H2A, H2B, H3, H4 | |
| What is a chromatasome? | DNA octomere + H1 | |
| What is a linker DNA? | H1, found between chromatosomes | |
| How does such a long double stranded molecule, in fact 46 of them, get packed into a tiny nucleus? | Due to it’s TERTIARY structure. Supercoiling- either remove some coiling or add some; one form of tertiary structure. | |
| Supercoiling is found where? | in bacterial cells, plasmids, and even in portions of linear DNA. | |
| What does supercoiling depend on? | it depends on topoisomerase. These are special enzymes of 2 types. Type I and Type 2 | |
| What are characteristics of the bacterial chromosome? | 1) NO histones but are other proteins there that help compact it, 2) large and circular, 3) complexed with proteins to form large twisted loops, 4) Held NOT in nucleus but indefinite are of cell called NUCLEOID- area of cell. | |
| What are the characteristics of a eukaryotic chromosome? | linear, have centromeres, telomeres. Chromatin structure changes LOCALLY as genes are transcribed and changes all during cell cycle. | |
| Where can heterochromatin be found? | found in telomeres, centromeres, and untranscribed areas, also in Barr body. | |
| Chromatin proteins | histones, nonhistone chromosomal proteins, nucleosome….? More? | |
| Histones | are the most abundant protein. H1, H2A, H2B, H3B, H4 | |
| Nonhistone chromosomal proteins | either act as STRUCTURAL or PROCESSING (TC or replication) proteins. Ex= scaffold protein, kinetochore, telomere caps, molecular motors to move chromosomes during meiosis and mitosis | |
| What is a nucleosome? | core particle consisting of DNA wrapped 2 times around an octamer of 8 histones (2 of all except H1) | |
| What does H1 do? | H1 acts as a clamp to lock nucleosomes in place. | |
| What are chromatosomes? | nucleosomes + H1. | |
| Nucleosome forms | forms a 30 nm strand, also known as a SOLENOID; spiral of nucleosomes. | |
| 30 nm strands loop back and forth to attach to scaffolding proteins (not shown in book) by means of | SARs (scaffold attachment regions) on the DNA. | |
| Changes in chromatin structure. Why does it relax? | chromatin RELAXES to allow TC and replication. | |
| Chromatin relaxation can easily be seen in? | polytene chromosomes. | |
| Polytene chromosomes | easily seen. These chromosomes are only found in flies and only in their salivary glands and footpads. These chromosomes are very thick because they undergo repeated round of DNA replication WITHOUT CELL DIVISION! | Therefore, have thousands of copies of the chromosome, side by side. Chromosome “puffs” equate with TC. |
| What is epigenetics? | stable alterations of chromatin structure that may be passed on to cells or individual organisms. | |
| Centromere Structure | 1) Critical for CHROMOSOME MOVEMENT during mitosis and meiosis. 2) centromeres appear to INHIBIT ANAPHASE until spindle fibers from the poles attach. 3) Two major classes of centromeres= Point centromeres, and regional centromers. | |
| Point centromeres | (Saccharomyces= 125 bp) –relatively small, repeated several times in centromeric region. | |
| Regional centromeres | in fission yeast, central core of 4,000 to 7,000 base pairs flanked by blocks of centromere-specific, often tandem repeat sequences. In humans, there are hundreds of thousands of repeats. | |
| Are centromeres defined by DNA sequence? | centromeres are NOT defined by DNA sequence but by epigenetic changes in chromatin structure. | |
| Function of telomere | 1) Stability against degradation of chromosomes. 2) Critical in replication because last few nucleotides on end are unable to be replicated. So chromosomes get shorter every time the cell divides. | Shortening is prevented by TELOMERASE found in germ cells and single celled organisms. 3) consists of tandem repeats. Human one is TTAGGG repeated 250-1500 times. Number of repeats depends on the cell type and chromosome. |
| Shortening of the chromosome in cellular division is prevented by? | telomerace | |
| What is shelterin? | multiprotein complex which binds to mammalian chromosome telomeres so they won’t be repaired as a double-stranded DNA break would. | |
| Artificial chromosomes | know what these are. YAC= yeast artificial chromosome, BAC= bacterial artificial chromosomes. | MACs= mammalian artificial chromosome. Includes 3 essential elements of chrom= centromere, telomere, and ori sites. **New artificial chromosomes can be inserted into a cell. |
| What is the C value? | the haploid amount of DNA per cell. Doesn’t always equate with complexity of organism. | |
| Denaturation of DNA | heating DNA molecules enough that H bonds break between the 2 strands; now have ssDNA (single stranded). Also known as “melting” the DNA. | |
| Renaturation of DNA | reannealing of the two DNA strands. | |
| Hybridization | when 2 ssDNA molecules from different sources anneal because they are complementary. | |
| What are the 3 types of DNA sequence in Eukaryotes? | 1) Nonrepetitive, unique sequence DNA 2) Moderately repetitive DNA 3) highly repetitive DNA (also known as satellite DNA) | |
| Nonrepetitive, Unique sequence DNA | includes protein coding genes and gene families; only show up once to a few times in the genome. Function and nonfunctional | |
| Moderately repetitive DNA | 150-300 bp long generally. Thousands of times repeated. | |
| What is tandem repeat? | ABCABCABCABC | |
| What is interspersed repeat? | repeat is scattered throughout the genome | |
| Functional, moderately repetitive DNA | ex= tRNA, rRNA, and histones | |
| Nonfunctional, moderately repetitive DNA | LINES and SINES | |
| LINES. What does it encode? What percent of human DNA is LINES? | 21% of DNA, long interspersed elements; NON-VIRAL RETROTRANSPOSON. 1) Encodes RNA binding protein. 2) Encodes RT (reverse transcription) homologue with endonuclease activity. | |
| LINES, what is the average LINE? | about 900 bp long. But can find them up to 6,000 bp long | |
| SINES, how long is the average SINE? | short interspersed elements. Are RETROTRANSPOSON. Average SIN is about 300 bp long and does NOT encode a protein!! | |
| What is an Alu sequence? | has an Alu restriction site in it; about 11% of human DNA | |
| SINES are viral retrotransposons | encode all viral proteins BUT envelope protein… so can’t bud from a cell. Integrase and reverse transcriptase proteins allow it to move in the genome. | |
| Transposons | can jump around in the cell. | |
| Viral retrotransposons | has viral genes in them but have LOST the envelope(env) gene. | |
| Highly repetitive DNA. How many repeats does it have? | also known as SATELLITE DNA. Usually <10 bp repeats. Has hundreds of thousands to millions of copies. Tandem or dispersed into clusters. USUALLY HAD NO FUNCTION!! | |
| What are some examples of highly repetitive DNA (satellite DNA)? | centromeric DNA; telomeric DNA; microsatellite repeats (dinucleotide repeats); VNTR DNA (minisatellite repeats). | |
| What are examples of functional DNA? | tRNA, rRNA, histones, ? centromeric, and telomeric? | |
| What are examples of NONfunctional DNA? | VNTR (minisatellite DNA), microsatellite DNA. | |
| General characteristics of transposable elements | 1) about 45% of human DNA! 2) Able to move around the genome. 3) May cause mutations by insterting within a gene or by promoting DNA rearrangements. 4) have SHORT DIRECT REPEATS and may have TERMINAL INVERTED REPEATS | |
| Short direct flanking repeats | due to insertion process; not a part of transposon | |
| Terminal inverted repeats | recognition sequence of transposases | |
| Transposition | movement of transposable element from one location to another | |
| Transposons transpose via | DNA intermediates. Those that still move, encode own TRANSPOSASE and may have other genes. | |
| Replicative transposition | a new copy of transposon introduced at new site while old copy stays at old site. | |
| Nonreplicative transposition | transposon excises self from one site and moves to another. MOST COMMON IN PROKARYOTES! | |
| Retrotransposons transpose via | RNA intermediates. DO NOT encode own transposase and may have viral genes like RT. Most common in EUKARYOTES | |
| Histones | most abundant protein. |
Created by:
organismalbiology
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