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26 Cards in this Set
- Front
- Back
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What is chromatin?
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DNA + histones + non-histone chromatin proteins
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What are nucleosomes and their structure
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DNA wrapped around histone octamers to form core particles connected by linker DNA. There are 200 base pairs of DNA. The entrance and exit of the histone is capped with Histone H1
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Describe the structure of the histone octamer
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consists of H1 H2A, H2B, H3,H4 and makes of AA Lys and Arg mostly (positively charged which facilitates binding to negatively charged DNA. 145 base pairs wrap around the histones in a left-handed negatively supercoiled helix because of underwinding of DNA to form less LK
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What is linker DNA?
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segments that connect the core nucleosomes.
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What is the significance of histone H1?
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can undergo modifications (phosphoralyation, methylation, acetylation) which effects solenoid organization
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When are chromosomes the most coiled?
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metephase
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Where are histones able to undergo modifications?
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The N terminus of histones project outward and they contain Lys, His, Arg, Ser, AA which are modified by enzymes:
1. acetylation of Lys 2.phosphorylation of Ser 3.methylation of Lys and Arg |
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Describe the acetylation modification of histones.
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The Lys is neutralized so the AA has less affinity towards DNA and the DNA loosens its strand becoming 'relaxed'. Also other proteins can bind that regulate transcription
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What is the histone code?
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The covalent modifications to histone amino tails.
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What are the higher order chromatin structures?
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solenoid, extended loop, condensed loop, chromosome
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What are solenoids (chromatin fibers)?
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Nucleosomes that are packed together (30nm)
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What are the differences between extended and condensed loops?
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The solenoids during interphase are arranged in 2 types of loops. Extended loops are diffuse, in nucleus called euchromatin and transcriptionally active (white regions in EM, 300nm). Condensed loops are compacted, heterochromatin in nucleus (dark spots) and transcriptionally inactive (700)
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How many base pairs does the human genome have and how does it compare to other species?
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Humans have 10^9. And complexity has no correlation with number of base pairs. ex) algae has more than us.
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What % of the human genome is repetitive, moderately repetitive, and non-repetitive (unique)
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10% repetitive- simple repeating sequences
~40% is moderately repetitive-just junk ~50% is unique but only 25,000-35,000 genes |
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What is a gene?
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DNA sequence that encodes for a functional RNA or protein product
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What is an allele?
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one copy of a gene
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What are pseudogenes?
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nonfunctional copy of a gene
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What are gene families?
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group of related genes derived from a common ancestor that may be expressed at different stages of development or in different cell types
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What are tandemly repeated genes?
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multiple copies of the same gene, protein production may require large quantities
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Describe the structure of a gene.
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Genes have a promoter region which controls transcription. It is in the spacer DNA. There is then a coding sequence called the exons and a noncoded sequence called the introns.
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What is spacer DNA?
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stretches of DNA that lie between genes that consists of repetitive and nonrepetitve DNA sequences. This contains the promotor region
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What is the difference between introns and exons.
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Introns are noncoding sequences and exons are coding sequences. While both are transcribed to the primary RNA transcript, it is process to form mRNA and the introns are removed.
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Describe how higher order chromatin structures contribute to the condensation of DNA
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DNA wraps around histones which have linker DNA and histone 1 to make nucleosomes. Nucleosomes curl into solenoid which form into extended loops that are attached to the chromosome scaffold. This scaffold is in the condensed loops but more tight
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What are the major types of highly repetitive genes?
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DNA of centromeres and telomeres
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What are the major types of moderately repetitive genes?
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Interspersed elements (Alu sequence)
Long interspersed (LINES) retroviral elements trasnsposons |
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What are the major types of non-repetitive genes?
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exons and introns
regulatory elements pseudogenes spacer DNA |
