Bmsc 220 Nucleus and Genome
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Nucleus is the site of:
- DNA replication
- RNA synthesis (transcription)
- RNA processing
- ribosome assembly
Where does Protein synth takes place?(translation)
- -selective traffic of proteins and RNAs through nuclear pore complexes in the nuclear envelope establishes nuclear composition
- - RNA out (mostly)
- - proteins in (but also back out)
- - highly regulated and energy dependent
nuclear pore complex-
a large macromolecular complex that differs significantly from typical membrane channels and transporters
- •a fibrous mesh that provides structural support located on inside of nuclear membrane
- •consists of fibrous proteins called lamins (several types), and other proteins.
outer nuclear membrane
- -phospholipid bilayer that is continuous with the endoplasmic reticulum.
- -enriched in membrane proteins that bind the cytoskeleton
inner nuclear membrane
phospholipid bilayer that has proteins that bind the nuclear lamina.
site of ribosome assembly
specifies a specific type of trait, and is one gene copy that is inherited from each parent(but there are many different alleles for any one gene).
the genetic composition of an organism
- -Physical representation of genotype
- -can include biochemical and physiological traits.
groups of phenotypic traits that are inherited together
carriers of genes and consist of long DNA molecules and associated proteins
the synthesis of a duplicate copy of a DNA molecule (DNA polymerase)
the synthesis of an RNA molecule from a DNA template (RNA polymerase)
is the synthesis of a polypeptide chain from an mRNA template (ribosomes)
Semiconservative replication of DNA
- •semiconservative because one strand of parental DNA is “conserved” (i.e. is one-half of) in each new progeny DNA molecule)
- •Therefore each new DNA double helix = 1 parent + 1 daughter strand
enzymes that catalyze the synthesis of RNA from a DNA template
Three major cellular RNAs
- Messenger RNAs (mRNAs)
- Ribosomal RNA (rRNA)
- Transfer RNAs (tRNAs)
-Other types of regulatory and catalytic RNAs are also present in cells
Messenger RNAs (mRNAs) .
RNA molecules that serve as templates for protein synthesis
Ribosomal RNA (rRNA)
is a component of ribosomes.
Transfer RNAs (tRNAs)
serve as adaptor molecules that align amino acids along the mRNA template.
corresponding information from nucleotide triplets called codons that encode individual amino acids in proteins
- -nucleotide triplets that carry meaning
- -the basic units of the genetic code.
- 64 codons
- 1 start(met) AUG
- 3 stops
long DNA sequences that lie between genes within a chromosome
- -segments of protein-coding sequence
- -Only 10-20% (on average)of a typical gene’s RNA-coding region is the actual protein coding region
- -~1.2 % of the human genome is exons that actually encode proteins
Introns (or intervening sequences) .
- -segments of non-protein-coding sequences found between exons
- -make up the majority of a gene’s RNA-coding
- -~20% of human genome is introns
the joining of exons in a precursor mRNA molecule by cutting out introns
Trends of genome properties between organisms
-as genome size and gene number increases, % of genome used for protein coding decreases
non-protein coding regions
-found to encode regulatory RNAs that play important roles in regulation of other genes
- - eukaryotic chromosomal DNA complexed with proteins
- -typically about twice as much protein as DNA.
What does the basic structure of chromatin serve to do?
- - pack DNA into a small space
- -total length of human DNA is 2 metres, packed into a 5-10 um nucleus
How is chromosome number related to Genome size?
It is unrelated?
the basic structural units of chromatin, and consist of DNA+histones
- -small proteins containing a high proportion of the basic amino acids, arginine+ and lysine+.
- -This facilitates binding to the negatively charged DNA sugar-phosphate backbone.
- -H1, H2A, H2B, H3, H4
•Nucleosome core particles
contain 147 base pairs of DNA wrapped around an octamer consisting of two molecules each of histones H2A, H2B, H3, and H4.
166 bp + histone H1
- -transcriptionally active interphase chromatin (usually as 10 and 30 nm fibres, or slightly more condensed)
-highly condensed, transcriptionally inactive chromatin, and it contains highly repeated DNA sequences.
- -Constitutive heterochromatin
- -Facultative heterochromatin
contains DNA that is not transcribed in any cell type, such as some DNA sequences at centromeres
-contains DNA sequences that are not transcribed in the cell being examined but may be transcribed in other cell types
- - is a specialized region of the chromosome that plays a critical role in ensuring the correct distribution of duplicated chromosomes to daughter cells during mitosis
- -frequently contain repetitive DNA.
- •Vary in size from 125 bp (S. cerevisiae) to millions of base pairs (humans) with no consensus DNA sequence
centromeric histone H3(CenH3)
a histone variant within nucleosomes contained in centromeres by all eukaryotes studied to date
- - a protein structure associated with the centromere, to which microtubules bind.
- -act as a molecular motor during mitosis and meiosis; not associated with centromere during interphase
- -the sequences at the ends of eukaryotic chromosomes
- -Critical role in maintaining stability of linear chromosomes
- -protects the end of the chromosome from deterioration or from fusion with neighboring chromosomes” … become shorter with each cell division
Telomere DNA sequences
- DNA sequences of various eukaryotes are similar
- - repeats of a simple-sequence DNA with clusters of G residues on one strand.
Open-reading frames (ORFs)
long stretches of nucleotide sequence that can encode polypeptides (no UAA, UGA, UAG) used to identify putative protein-coding genes in genome sequencing projects.
size of genome
- •Simplest present day prokaryote
- •Second smallest genome of known cells (580 kbp) with 470 genes
- •Likely represents the minimal gene set required to maintain a self-replicating organism
- -Encodes proteins for replication, transcription, translation, membrane transport, and energy metabolism
- -Lacks many genes for biosynthetic pathways
- -YET-150 genes still of unknown function
significance of Drosophila in evolution of multicellularity discussion
-a complex animal, yet has only about twice the number of unique genes found in yeast, a much simpler organism! (1300-6000)
The Human Genome
how many chromosomes?
how many genes?
- -spread over much larger distances/ contain more intronsequence than genes in Drosophila orC. elegans
- -Share approximately 40% of genes of lower eukaryotes (most involved in basic cellular processes)
Mice, rats, humans: - ___% of genes in common
Chimps, humans: almost __% identical at the nucleotide sequence level
- -vary at an average of only 1 nucleotide in 100
Two individual human beings-vary at an average of 1nucleotide in ____
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