Genetics Flashcards
Nucleosome
8 histones wrapped in DNA
Chromatin
The entire DNA/protein complex (including small amount of rna)
Heterochromatin
Chromatin that is tightly condensed
Euchromatin
Chromatin that is uncoiled and able to be transcribed.
Only coiled during nuclear division.
DNA methylation
Most common example of epigenetic regulation through chemical change.
Involves the addition of an extra methyl group to particular cytosine nucleotides.
Causes DNA to be wound more tightly so those sections cannot be transcribed.
of chromosomes in human somatic cell
46 double stranded DNA molecules
23 homologous pairs of chromosomes
Homologues
Two chromosomes that code for the same traits
Diploid
Cell that contains homologous pairs of chromosomes
Haploid
Cell that doesn’t contain homologues
Histones
Globular proteins that sections of DNA not in use are wrapped tightly around.
Have basic functional groups that give these proteins a net positive charge at the normal pH of the cells.
Net positive charge attracts the negatively charged DNA and assists in the wrapping process.
Cell Cycle - G0
non-growing phase
most cells spend majority of life in this phase
most protein production take place during this phase when the cell is not exerting energy in self-replicating
Transcription
process by which RNA is manufactured from a DNA template.
3 main stages: initiation, elongation and termination.
Main level of activation or deactivation of genes.
Transcription: Initiation
a group of DNA binding proteins called transcription factors identifies a promoter (a sequence of DNA nucleotides that designates a beginning point for transcription.
major enzyme of transcription is RNA polymerase. it unzips the DNA double helix.
Transcription: Elongation
RNA polymerase transcribes one strand of the DNA nucleotide sequence into a complementary RNA nucleotide sequence. Reads DNA 3’ - 5’, builds RNA 5’ - 3’.
Transcribed strand is template or (-) antisense strand, other strand is coding or (+) sense strand.
No proof reading mechanism (errors in RNA are not called mutations and not transmitted to progeny).
Transcription: Termination
end of transcription.
Post-transcriptional processing
Takes place in the nucleus.
5’ cap serves as an attachment site in protein synthesis during translation and as a protection against degradation by enzymes that cleave nucleotides.
3’ end is similarly protected from exonucleases by the addition of a long series of adenine nucleotides (poly A tail).
Introns are removed through splicing which involves snRNPs (and lariat).
Alternative splicing
allows the cell to incorporate different coding sequences (omitting certain exons, incorporating certain introns, utilizing variable splicing sites) into the mature mRNA.
an important contributor to the diversity of protein products.
Start codon
5’ - AUG - 3’
Stop codons
5’ - UAA, UAG, or UGA - 3’
Translation
takes place using a ribosome (free-floating in cytosol or attached to outer surface of ER).
3 stages: initiation, elongation and termination.
within each ribosome there are 3 sites where tRNA can bind. A site - Anticodon matches up with the codon. P site - a Peptide bond between amino acids is formed. E site - the tRNA which now lacks an amino acid can Exit the ribosome.
Cell Cycle - S phase
DNA replication takes place during the S phase of the interphase portion of the cell cycle.
5 main steps of DNA replication
- Helicase unzips double helix
- RNA polymerase (primase) builds a primer
- DNA polymerase assembles the leading and lagging strands
- RNAse H removes the primers
- DNA ligase joins the okazaki fragments together.
Telomeres
repeated 6 nucleotide units that protect the ends of chromosomes.
Mitosis
nuclear division without genetic change.
stages: PMAT
