What are the steps of gene expression?
When and where does gene expression occur?
Transcription occurs in the nucleus throughout interphase
Translation of RNA (protein synthesis) occurs in the cytoplasm throughout the cell cycle.
When and where does DNA replication occur?
Occurs during S phase in the nucleus
What are the steps of interphase?
G1 phase: cellular growth (ex. skin epithelial cells, Gi tract, follicle cells, nucleated red cells)
G0 phase: resting, non-dividing cells (most cells including muscle, nerve, liver cells)
S phase: DNA synthesis; two sister chromatids linked at centromere
G2 phase: replicated DNA is checked for errors before cell division
What allows cells to go from G1 to S phase?
A GF (hormonal signal; ex. EGF, PDGF) that binds to tyrosine protein kinase receptor
What chemotherapeutic agents target the S, G2, and M phases of the cell cycle?
S phase: methotrexat, 5-flurouracil
C2 phase: belomycin
M pahse: paclitaxel, vincristine, vinblastine
What chemotherapeutic agent targets non cell-cycle speciifc phases?
What comprises a nucleotide?
nitrogenous base, five carbon sugar (pentose) and phosphate
(Base covalently link to 1' carbon of sugar
and phosphate groups attached to 5' carbon of sugar)
What are the types of bases?
Purines: adenine, guanine (2 rings)
Pyrimidines: cytosine, uracil, thymine (1 ring)
What comprises a nucleoside?
Nitrogenous base + sugar
(Base covalently link to 1' carbon of sugar)
Where are the purines found?
DNA & RNA
Where are the pyrimidines found?
Cytosine: DNA & RNA
What is a nucleic acid?
polymers of nucleotides joined by 3',5' phosphodiester bonds
phosphate group found at 5' end and hydroxyl group found at 3' end
How can you tell the difference between DNA and RNA?
1. type of pyrimidine base
2. Type of pentose
(Ribose with 2' OH=RNA; Deoxyribose=DNA)
How is the base sequence of a nucleic acid written by convention?
5' --> 3'
What are the features of double stranded DNA?
1. Two strands are antiparallel
2. The two strands are complementary
[A pairs with T (2 hydrogen bonds) and G pairs with C (3 hydrogen bonds)
3. Chargaff's rules
Total purines = Total pyrimidines
% A = % T (%U)
% G = % C
What is Watson-Crick DNA?
Right-handed double helical DNA
Hydrophilic sugar-phosphate backbone=outside of double helix
hydrogen-bonded base pairs = center of molecular
What is Z-DNA?
Left-handed double helical form of DNA
occurs in G-C rich sequences
What is the action of daunorubicin and doxorubicin?
Anti-tumor drugs for leukemia
Intercalate between bases of DNA and interfere with topoisomerase II activity, which prevents proper DNA replication
What is the action of Cisplatin?
Binds tightly to DNA, which causes structural distortion and malfunction
Treats bladder and lung cancers
How is DNA denatured?
heat, alkaline pH, chemicals (formamide, urea)
In what experiments is renaturing (annealing) important?
Southern blot, PCR
What is hybridization?
probe DNA binds to target complementary DNA sequences
What is negatively supercoiled DNA?
DNA that is wound more loosely than Watson-Crick DNA
required for most biologic reactions
What is positively supercoiled DNA?
DNA that is wound more tightly than Watson-Crick DNA
What is the function of topiosomerases?
change the amount of supercoiling
Make transient breaks in DNA strands by breaking and resealing the sugar-phosphate backbone
What is chromatin?
nuclear eukaryotic DNA that is associated with histones and non-histone proteins
What histones are present in nucleosomes and what is the their function?
Two copies of H2A, H2B, H3 and H4
Histones = Positively charged because rich in arginine and lysine
DNA = negatively charged because PDE bonds
What is a 10 nm chromatin?
DNA with (H2A, H2B, H3, H4) x 2
Octomer of 8 proteins
Sensitive to nuclease
What is 30 nm chromatin?
nucleosome with H1 protein
More compact than 10 nm chromatin
What are the two types of chromatin in interphase?
Euchromatin and heterochromatin
More opened and available for gene expression
Active gene expression (transcription)
Corresponds to nucleosomes (10 nm fibers) [also 30 nm fibers]
More highly condensed and assocaited with areas of chromosomes that are not expressed
Inactivate gene expression
Barr body=inactive X chromsome in female somatic cell
Describe the DNA during mitosis.
highly condensed to allow separation of sister chromatids
only time in the cell cycle when the chromosome structure is visible
no gene expression