Bmsc 220 Nucleus and Genome

• DNA replication 
• RNA synthesis (transcription) 
• RNA processing 
• ribosome assembly

cytoplasm

• -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

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.

• -phospholipid bilayer that is continuous with the endoplasmic reticulum.
• -enriched in membrane proteins that bind the cytoskeleton

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 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

• Messenger RNAs (mRNAs)
• Ribosomal RNA (rRNA)
• Transfer RNAs (tRNAs)

-Other types of regulatory and catalytic RNAs are also present in cells

RNA molecules that serve as templates for protein synthesis

is a component of ribosomes.

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

• -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

-as genome size and gene number increases, % of genome used for protein coding decreases

-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.

• - pack DNA into a small space
• -total length of human DNA is 2 metres, packed into a 5-10 um nucleus

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

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

• -decondensed
• -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

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
• -

• DNA sequences of various eukaryotes are similar
• - repeats of a simple-sequence DNA with clusters of G residues on one strand.

long stretches of nucleotide sequence that can encode polypeptides (no UAA, UGA, UAG) used to identify putative protein-coding genes in genome sequencing projects.

• •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

-a complex animal, yet has only about twice the number of unique genes found in yeast, a much simpler organism! (1300-6000)

• 24
• 20,000-25000
• -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)

90

• 99
• -vary at an average of only 1 nucleotide in 100

1000