Lecture 1 Flashcards
What was discovered in the late 19th century?
Hereditary information carried on chromosomes
What is a gene?
The information-containing elements that determine the characteristics of a species
When are chromosomes visible by light microscopy?
When the cell undergoes division
What do chromosomes contain?
DNA and protein
What are the building blocks of DNA?
Nucleic Acids
What are nucleotides joined together by?
Phosphodiester linkage between 5’ and 3’ carbon atoms
What do polynucleotides have?
Polarity, 5’ phosphoryl end, and 3’ hydroxyl end
What is the structure of DNA?
2 long polynucleotide chains with 4 types of nucleotide subunits
Nucleotides are 5 carbon sugar and nitrogenous base covalently linked via glycosidic bond
Sugar is deoxyribose
Adenine, cytosine, guanine, and thymine bases
Double Helix - 1 turn/10bp
Antiparallel
What are the purines in DNA?
Adenine and guanine
What are the pyrimidines in DNA?
Cytosine and thymine
What is a genome?
A complete set of information in an organism’s DNA
True or False?
At replication, the entire genome must be duplicated and passed to the daughter cell.
True
How many nucleotides does the human genome have?
3.2x10^9 nucleotides distributed over 24 different chromosomes
What is a chromosome?
Single long linear DNA molecular associated with proteins that fold and pack it into compact structure.
How many copies of each chromosome does the human cell have?
2 copies - maternal and paternal homologs-
Except germ cells and RBCs
How many pairs of autosomes are the in the human cell?
22 pairs
How many sex chromosomes does a human have?
2
What information is found on chromosomes?
Genes
-encoding proteins and RNA molecules
Interspersed DNA that does not contain genes
-regulatory information , junk DNA
How much of the average gene size comprise of coding region?
5%
What is the percentage of DNA sequence in exons (protein coding sequences)?
Whole genome
1.5%
What are functional sequences?
Sequences that are relatively conserved during evolution
What are non-functional sequences?
Sequences that mutate randomly w/o consequence
What are coding regions?
Exons that are typically 145 bp that are floating in a sea of large introns
What is conserved synteny?
Large blocks of genes are conserved in the same order on the chromosome (compared to ancestors)
What happens in interphase?
Chromosomes are replicated; they are decondensed and cant be easily distinguished
What happens during mitosis?
Become highly condensed and separated into two daughter nuclei
What are 3 important components of chromosomes?
DNA replication origin: where duplication of the DNA begins
Centromere: allows one copy of each duplicated and condensed chromosome to be pulled into each daughter cell
Telomeres: repetitive sequences at the end of a chromosome that enable the ends to be efficiently replicated
What is chromatin?
Protein + nuclear DNA
What is the most basic unit of chromosome packing?
nucleosome. Repeats after 200 nt
How many histone proteins are in each individual nucleosomes core particle?
8 histones
What are the 8 histones?
2 molecules each of H2A, H2B, H3, H4
What is linker DNA?
Exposed DNA between nucleosome core particles
About 80 nt long
What are histones?
Small proteins with common structural motif called histone fold.
What bonds form between histones and DNA?
142 hydrogen bonds in each nucleosomes
Hydrophobic interactions
Salt linkages - lysine and arginine comprise more than 1/5 of histone residues, effectively neutralize negatively charged DNA backbone
Are histones are conserved or non-conserved?
Highly conserved, most changes would e lethal
True or False
Nucleosomes are static?
False,
It is in a dynamic situation to allow for rapid localized access to DNA for gene expression. Nucleosomes are in a constant state of flux
What allows for a further loosening of DNA/histone contact?
Chromatin remolding complexes. Related to Helicase and are ATP dependent
Bind to both protein core and DNA
What is the zig-zag model?
Theory how the nucleosome packs and becomes a dense fibrous.. Stacking that may be facilitated by histone tails and histone 1 is present in 1:1 ration with nucleosome cores
What is the linker histone?
H1
Larger histone
Less well conserved
What is needed to pack DNA?
Incredible amount of condensing. Mitotic chromosomes are condensed 500 x more than in interphase
What are the DNA binding proteins involved in forming chromosomes?
Histones and non histones
What forms beads on a string?
Chromatin isolated directly from interphase nucleus that is partially unfolded
What breaks down DNA by cutting between Nucleosomes and degrading the exposed DNA (linker protein)
Nucleases
What is the nucleosome core particle?
Disk shaped particle that DNA wraps 1.7 x around
What are the tails of histones subject to?
N terminal a.a tail that extends out from the core are subject to covalent modifications important for chromatin regulation
What adds to various chromosome structures?
Specialized variant histones
