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42 Cards in this Set
- Front
- Back
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How many chromosomes are in humans?
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22 pairs and 2 sex chromosomes resulting in 46 total
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How much DNA is in each cell?
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1 linear piece
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Chromosomes are packaged into ____ by proteins that compact the DNA.
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chromatin
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What are homologous chromosomes?
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in each cell, except germ cells, two copies of each chromosome exist, one inherite maternally and one paternally.
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Non-homologous?
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sex chromosomes in male
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What is a gene?
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a segment of DNA which contains the instructions for makng a protein or RNA molecule.
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Junk DNA.
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a majority of DNA in a human cell does not encode for genes
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Interphase chromosomes
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-relatively decondensed and undergoing replication
-individual chromosomes cannot be distinguised |
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Metaphase Chromosomes
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-highly condensed for distribution to daughter cells
-easily visualized |
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Centromeres
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-protein core
-octamer containing two of each histone protein (H2A, H2B, H3, and H4) -a 5th histone is bound to the DNA as it enters the nucleosome core. -147 base pairs of DNA wrap slightly less than 2 turns around core. -linker DNA ranges around 80 base pairs |
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What is contained in the cells nucleus?
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-Nuclear Envelope - 2 lipid bilayers - punctured at intervals by large nuclear pores, which transport molecules between the nucleus and the cytosol, directly connected to ER, mechanically supported by the nuclear lamnia
-Chromatin- composed of “beads” (called nucleosomes) on a double stranded DNA string -Complex of DNA and protein -Nucleolus- site of ribosomal RNA synthesis. 3 major components: A fibrillar center (chromatin) Dense fibrils (ribonucleoproteins) Granules (RNA containing ribonucleoproteins) |
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What is contained in the nucleolus?
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-rRNA synthesis
-chromatin (a fibrillar center) -ribonucleoproteins (dense fibrils) -RNA containing ribonucleoproteins (granules) |
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Function of centromere?
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Facilitates correct distribution of sister chromatids to daughter cells during mitosis.
Structure: Constricted region on chromosome. Highly repetitive satellite DNA sequences. Sequences for protein attachment. Kinetochore: Formed by the binding of microtubules of the mitotic spindle to centromere related proteins. Molecular motor proteins associate here, driving chromosome movement. |
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Location and structure of centromere?
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-constricted region on chromosome
-highly repetitive satellite DNA sequences -sequences for protein attachment |
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Kinetochore?
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formed by the binding of microtubles of the mitotic spindle to centromere related proteins.
-molecular motor proteins associate here, driving chromosome movement. |
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What type of cells express high levels of telomerase?
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Cancer cells often express high levels of telomerase and it’s subunit hTERT.
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What is the protein to chromatin ratio in eukaryotic cells?
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equal
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What is the structure of chromatin when it is transcriptionally active? And will be in this form at high or low salt concentration?
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"beads on a string," low salt concentration
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Transcriptionally inactivechormatin?
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more condensed at physiological salt concentrations.
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What are the classes of proteins associated with chromatin?
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histone and nonhistone
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What is the purpose of a nucleosome?
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DNA within a nucleosome is less susceptible to degradation.
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How is DNA and histones attached?
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Nearly half of the bonds between DNA and histone form betwen the amino acid backbone of the histones and teh phosphodiester backbone of the DNA., hydrophobic interactions and salt linkages also hold DNA and protein together.
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When is the nucleosome formed?
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In cells, the nucleosome is formed shortly after the replication fork passes. This requires proteins whose function is nucleosome assembly.
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What are histones and list their characteristics?
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The major protein of chromatin.
Characteristics: Small ( < 25 kD) Positively charged with basic amino acids lysine and arginine (20-30%) Each core histones have a N-terminal or amino acid tail extending out from the DNA - histone core, these tails are subject to several different types of covalent modifications that control critical aspects of chromatin structure. |
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Euchromatin
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Euchromatin- “good chromatin”, transcriptionally active and about 10% of total chromatin. The site of synthesis of nonribosomal RNA. (tRNA, mRNA)
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Heterochromatin
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Heterochromatin- “different chromatin”, condensed and transcriptionally inactive, about 90% of total chromatin.
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Where is heterochromatin usually found?
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associated with the nuclear lamina
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Where is euchromatin usually found?
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Euchromatin in undergoing active gene expression and it located in extended loops towards the center of the nucleus.
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Nuclear matrix:
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Scaffold made of protein and RNA for the support of chromosomal DNA.
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Condensation of Mitotic Chromosome
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Sister chromatids are held together via their centromeres.
Organized into loops of chromatin supported by scaffolding. Begins in early M phase Gene expression shuts down Aided by condensin proteins Make large right handed loops in DNA via hydrolyzing ATP |
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Interphase Chromatin Condensation:
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Euchromatin- Relatively decondensed.
Distributed throughout nucleus. Mostly 30 nm fiber. Large loops of 50-100 kb. Active transcription is occurring in a more decondensed state, extended nucleosome state. |
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Metaphase Chromatin Condensation:
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Heterochromatin- Highly condensed.
Transcriptionally inactive. Large loops supported on protein scaffolds. 30 nm fibers fold on themselves to form compact metaphase chromosomes. (10,000-fold shorter in length) Contains centromeres and telomeres. |
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Are changes in histone amino acid sequence significant?
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-amino acid sequence has been evolutionarily conserved suggesting that the functionns of histones involve nearly all their amino acids.
-any amino acid change in histones is lethat |
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How are nucleosomes arranged on DNA?
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due to the presence of ATP-dependent remodeling complexes, the arrangement of nuleosomes on DNA can be highly dynamic, changing rapidly according to the needs of the cell.
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What is dosage compensation?
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Random inactivation of one of the two X chromosomes in every female somatic cell.
Both X chromosomes remain active in the oocyte. Randomly (paternal or maternal) occurs early in development (day 12-16) and remains nonrandom for all subsequent cells. |
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What is a barr body?
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the remaining heterochromatin mass which remains adjacent to the nucleuar envelop
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What does p represent?
What does q represent? What does cen represent? tel? Metacentric? Submetacentric? Acrocentric? Telocentric? |
Short arms: p (petit)
Long arms: q (queue) Centromere: cen Telomere: tel Metacentric: Centromere near median, chromatids have well defined arms. Submetacentric: Centromere is near terminal, chromatids have a distinctly shorter arm containing a stalk of DNA leading to terminal satellite sequences. Acrocentric: Centromere is not median; chromatids have one distinctly shorter p arm. Telocentric: Centromere is terminal, chromatids have only one arm. |
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What is hTERT?
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Human Telomerase Reverse Transcriptase.
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What does hTERT do
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Ribonucleoprotein which adds TTAGGG to the end of telomeres.
Implicated in cancers, progeria, and normal cellular aging. Many others including dyskeratosis and coronary artery disease. |
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What is a proto-oncogene?
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A gene whose product has the capacity to induce proliferation or transformation before genetic damage is sustained. (Can be an unaffected version.)
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What is an oncogene?
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A gene that has sustained genetic damage and can therefore induce cell proliferation or transformation. (Defective version.)
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What is a tumor suppresor?
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Generally encode proteins which inhibit cell proliferation.
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