CHAP 2 Flashcards
What is the function of DNA polymerase?
travels along the single DNA strand and adds free nucleotides to 3’ end of the strand (replication always occurs 5’ to 3’
What is upstream and what is downstream?
5’ direction is upstream, 3’ direction is downstream
What are pyrimidines?
single carbon-nitrogen rings (Cytosine and thymine)
What are purines?
double carbon-nitrogen rings (adenine and guanine)
What makes up the sides of the double helix? and the middle?
sides- sugar and phosphate held together by phosphodiester bonds, chemical bonds held together by hydrogen bonding create the steps
What allows the replication process to occur more quickly?
replication origins and bubbles
What mediates transcription and translation?
RNA
How does RNA differ from DNA?
RNA contains ribose instead of deoxyribose, and uracil rather than thymine, It is also a single strand.
What is transcription
RNA is formed form a DNA template (mRNA)
Describe sense and antisense strands
When transcription begins, RNA polymerase binds to a promoter site on the DNA which seperates the DNA strands. The DNA strand that serves as a template is the antisense strand and the remaining strand is the sense strand (should be identical to the mRNA being transcribed)
What helps the RNA molecule from being degrade during synthesis?
5’ Cap- a chemically modified guanine nucleotide
After a termination sequence is reached what happens to the RNA strand?
100 - 200 adenine bases are added to the 3’ side –> poly-A tail PRIMARY TRANSCRIPT IS FORMED
What is the chain of interactions that increase transcription?
enchancer –> activator –> coativator –> general transcription complex –> gene
Describe the helix-turn-helix motif.
Two alpha-helices connected by a short chain of AA– HOX genes can cause synpolydactyly (BIND TO DNA GROOVE)
Describe a helix-loop-helix motif.
One short and one long helix connected by a flexible loop –Mutation in TWIST gene (Saethre-Chotzen syndrome)
Describe a zinc finger motif.
Zinc molecules that stabilize AA structures (BIND TO DNA GROOVE)– Breast cancer gene, Wilms tumor gene (WT1), Vit D receptors (rickets)
Describe a leucine zipper motif.
2 leucine-rich alpha-helices held together by AA side chains (BIND TO DNA GROOVE) –RB1 (retinoblastoma genes)
Describe a beta-sheet motif.
Side chains extend from 2 beta sheets to form contacts with DNA helix –TBX5 (Holt-Oram syndrom) TBX3 (ulnar mammary syndrome)
What are euchromatins?
TRANSCRIPTIONALLY ACTIVE opened/decondensed chromatin regions, characterized by histone acetylation (attachment of acetyle groups to lysine residue in histones)
What are heterochromatins?
Less acetylated more condensed and transcriptionally inactive chromatin regions
Describe the change from a primary mRNA transcript to a mature mRNA transcript.
Introns are spliced OUT and exons are left to code for proteins. mRNA then moves into the cytoplasm
What are the three STOP codons?
UAG UUA UGA
What is translation?
mRNA interacts with tRNA to synthesize polypeptides
Where does rRNA bind to and what is its function?
rRNA binds to the initiation site on the mRNA– methionnine (AUG). It binds tRNA and mRNA
Osteogenesis imperfecta is a defect in what protein?
Collagen Type I
Which osteogenesis imperfecta subtypes is caused by mutations in two genes?
I-IV
What is amino acid is critical to proper folding of the triple helix in formation of collagen? (It is present at every 3rd position of the polypeptide)
Glycine **if replaced by another amino acid instability occurs bc glycine is the only AA small enough to accommadate in the center of the triple helix structures
What is the consensus sequence?
DNA sequence that direct splicing enzymes to specific locations
What are the three types of DNA that are seen in our genome
- Single-copy genes (45%) 2. Dispersed repetative DNA (45%) 3. Satellite DNA (10%)
What percent of the genome is composed of minisatellites and microsatellite DNA?
3%
Describe the Alu repeat
It is a SINE, wwith ALu repeats that contain DNA sequence that can be cut by the Alu restriction enzyme. They make up 10% of the genome
What happens during G1, S, and G2 stages?
G1: synthesis of RNA and proteins
S: DNA replication
G2: some DNA repair takes place, cell prepares of mitosis
Meiosis I is also called..
reduction division stage- 2 haploid cells from 1 diploid cell
Meiosis II is also called..
equational division stage- haploid cells are duplicated
What phase differentiates meiosis from mitosis, what specifically?
Prophase I, synapsis- homologous chromosomes line up side by side and formation of chiasma- crossing over of chromosomes to exchange genetic materials
What characterizes the beginning of metaphase in both meiosis and mitosis?
The completion of spindle formation
At what stage does the chiasmata disappear?
Anaphase I
What marks the beginning of telophase I?
the chromosomes reach the opposite side of the cell
What is the difference between interphase I and II?
in interphase II there is no DNA replication
How many chromosomes are present in a spermatogonia?
Diplod
At what stage does sperm become haploid?
After meiosis II, when they become spermatids
What stage is oogenesis arrested at before birth?
Prophase I
When does meiosis II begin in secondary oocytes?
Fertilization by sperm cell
What happens at ovulation?
Meiosis I is completed so there is a secondary oocytes (haploid) and polar body
