Genetics Flashcards
What are the phases of the cell cycle?
Interphase - consists of G1, S phase and G2. Mitosis - consist of prophase, metaphase, anaphase and telophase then cytokinesis.
What occurs during S phase?
The cell’s DNA is synthesized.
What occurs during prophase of mitosis?
The duplicated chromosomes condense and the mitotic spindle assembles.
What occurs during prometaphase and metaphase of mitosis?
In prometaphase the nuclear envelope breaks down so that the chromosomes can attach to the mitotic spindle. During metaphase the chromosomes align along the equator of the cell.
What occurs during anaphase of mitosis?
The sister chromatids separate and are pulled towards opposite ends of the cell.
What occurs during telophase of mitosis?
The two sets of chromosomes arrive at opposite ends of the cell. A new nuclear membrane assembles around each set, forming two new nuclei.
What occurs during cytokinesis of mitosis?
The cytoplasm divides into two daughter cells.
Describe meiosis.
Meiosis is the process by which chromosome number is halved to form a haploid gamete via two successive cell divisions. In prophase I - the chromosomes undergo recombination, with crossing over of homologous chromosomes. Metaphase I - the chromosomes align along the equator of the cell. Anaphase I - the homologous pairs separate and move to opposite poles of the cell. Telophase I - new nuclear membranes form, and each nucleus now contains 23 haploid chromosomes. Cytokinesis - cytoplasm divides. Prophase II - chromosomes condense and the mitotic spindle begins to form. Metaphase II - homologous chromosome align along the cell equator. Anaphase II - sister chromatids separate and begin moving to opposite ends of the cell. Telophase II - new nuclear membranes form. Cytokinesis - the cytoplasm divides again.
What is the different between mitosis and meiosis?
Mitosis = somatic cells; Meiosis = occurs in germ cells. Mitosis = one cell division resulting in 2 daughter cells; Meiosis = two cell divisions resulting in 4 products. Mitosis = no pairing of homologs and no crossing over; Meiosis = pairing of homologs with crossing over in prophase I. Mitosis = sister chromatids divide during anaphase; Meiosis = homologs divide in anaphase I and sister chromatids divide in anaphase II. Mitosis = products are identical and diploid; Meiosis = products are not identical and are haploid.
Describe DNA replication.
(1) Initiation - the initiator protein binds to the AT-rich sequences of DNA –> helicase unwinds the DNA making the sequence accessible –> replication forks form. (2) Elongation - in the leading strand: a RNA primer is added to the template –> DNA polymerase begins adding complementary base pairs in a 5’ to 3’ direction –> the strand elongates until it meets the next replication fork; in the lagging strand: the DNA polymerase also adds complementary base pairs in a 5’ to 3’ direction –> short segments of DNA are formed called Okazaki fragments –> DNA ligase joints the fragments together.
(3) Termination: once the elongating strand meets the next replication fork, the DNA polymerase is released –> RNAse enzyme removes the primers and finally DNA polymerase fills the gaps created by the primers.
Describe transcription.
The DNA is unwound, and RNA polymerase II binds to the DNA –> it builds RNA from 5’ to 3’ along the antisense strand to form a copy of the coding strand –> it continues transcribing until it reaches a stop codon –> the mRNA is cleaved off the DNA template.
What are the three main post-transcriptional processing events?
(1) 5’ capping
(2) 3’ polyadenylation
(3) splicing (removal or introns)
Describe translation.
After transcription, mRNA leaves the nucleus and travels to the ribosomes on the rough endoplasmic reticulum, where translation occurs. The ribosomes have 3 slots for tRNA to bind: A, P and E sites. tRNA has an amino acid attached to it, and an anti-codon sequence at the other end. The tRNA with a start codon binds to the ribosome at the P site –> the next tRNA with an appropriate anticodon matching the mRNA on the ribosome arrives at the A site –> a peptide bond forms between the amino acids on the tRNA at the P and A sites –> the growing peptide chain is shifted to the tRNA at the A site –> the mRNA is pulled across one codon and the tRNA at the A site moves to the P site; that at the P site moves to the E site and that at the E site is ejected –> this cycle continues as a new tRNA moves into the now empty A site –> when a stop codon is reached a release factor binds to the A site –> the bond between the polypeptide chain and tRNA is broken and the protein is released; mRNA and tRNA are released from the ribosome.
What is a missense mutation?
A single nucleotide in a gene is altered –> causes an amino acid in the protein to be replaced with a different amino acid.
What is a nonsense mutation?
The normal codon is replaced by a stop codon –> causes termination of the mRNA chain.
