Lecture 18: Chromosome Structure and Dynamics
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How is genetic information in DNA passed to the next generation?
Through DNA replication and cell division
What is the central dogma?
Genetic information flows in one direction: DNA -> RNA -> protein
What is a genome?
A genome consists of the DNA (or for some viruses, RNA) that contains one complete copy of all the genetic information of an organism or virus
Do mitochondria and chloroplasts have their own genome?
Yes!
Where are genetic instructions coded on the DNA of a gene?
They are coded in the sequence of nucleotides along the DNA
What are the 4 bases in DNA?
A, T, G, C
What are the 4 bases in RNA?
A, U, G, C
The message in DNA will be translated in mRNA which will then be translated into the language of ___ ____
Amino acid
What does the amino acid sequence determine for a protein?
Protein function and 3D structure
Why do organisms differ from each other?
Organisms carry genes with different nucleotides sequences, and in turn, different proteins
DNA in chromosomes is highly condensed and organized by?
Specialized proteins (histones and nonhistones)
Each human cell contains about 2m of DNA but the cell nucleus is only 5-8 micrometers in diameter. Tucking all this material into such a small space is the equivalent of trying to fold 24 miles of thread into a
tennis ball
What specialized proteins package DNA? How do they package the DNA?
Histones and nonhistones coil and fold DNA into higher levels of organization (aka chromatin)
What is chromatin?
Chromatin is a higher level of DNA organization (product of histones and nonhistones coiling and folding DNA)
Folding DNA into chromatins prevents what?
Prevents DNA from becoming a tangled, unmanageable mess (very necessary during mitosis)
Compacted DNA still allows for on-demand (______) access by enzymes and other proteins for transcription (via ____ ______)
Selective access, via rapid unpacking
What are the most abundant proteins in chromosomes?
Histones
Histones are rich in what amino acids?
Lysine and arginine
What are histones responsible for?
The first and most fundamental level of chromatin packing (the nucleosome). Histone octamer forms the nucleosome core particle
What is a nucleosome?
A nucleosome is made up of a core particle + Linker DNA. Histone forms the core particle
What is an octamer?
a protein complex made of eight histone proteins that forms the core of a nucleosome
What are the 4 core particle histones? How many are in each octamer?
H2A, H2B, H3, and H4 There are 2 of each in the octamer
Histones are rich in lysine and arginine; how does this impact the histone’s ability to interact with DNA?
Lysine and arginine allows histones to tightly bind to the negatively charged DNA sugar-phosphate backbone (independent of DNA sequence)
Each of the histones in the octamer have what kind of tails? What are these tails subject to and why are the tail mods important?
Long N-terminal amino acid tails The histone tails are subject to several types of reversible and covalent modifications. These tail mods control chromatin structure