Genetics Exam 2

euploidy

having a chromosome number that is n

aneuploidy

having a chromosome number that is not an exact multiple of n (2n-1 monosome or 2n+1 trisomy)

polyploidy

having more than 2 complete sets of chromosomes (3n, triploidy)

what can polyploidy produce?

unbalanced (aneuploid) gametes, triploid individuals will not produce viable (reproducing) offspring

what is the origin of chromosome number variation?

nondisjuntion, failure of chromosomes to segregate properly

what is an example of monosomy in humans?

turner syndrome, only one X in females, only non-lethal monosomy

what is an example of trisomy in humans?

trisomy X (female with XXX), down syndrome (21+)

what does mitotic nondisjunction lead to?

somatic mosaicism, individual has two genetically distinct populations of cells, (some will be monosomic some will be trisomic)

duplication

genetic material is present more than once in a genome

deletion

piece of a chromosome is lost

inversion

segment of chromosome is turned around 180 degrees

pericentric vs paracentric

pericentric means an inversion includes the centromere, paracentric means an inversion not including the centromere

translocation

movement of a chromosomal segment to a new location in genome, can be reciprical where segments are exchanged between non homologous chromosomes

robertsonian translocation

long arms of 2 acrocentric chromosomes fuse, generating a metacentric chromosome with 2 long arms and another with 2 very short arms

What is the difference between ribose and deoxyribose?

ribose has an OH on 2’ while deoxyribose has just an H

What are the purines?

adenine and guanine and they have a double ring structure

What are the pyrimidines?

cytosine, thymine, uracil and they have single ring structure

What bond connects nucleotides?

phosphodiester bonds

What number is the phosphate group or hydroxyl?

on 5’ there is free phosphate on 3’ there is free hydroxyl

How many hydrogen bonds do A-T and C-G have?

A-T has 2 and C-G has 3

How do eukaryotic chromosomes act in interphase vs mitosis/meiosis?

chromosomes are relatively uncoiled in interphase, condensed during mitosis and meiosis

euchromatin

chromatin that undergoes the normal process of condensation and decondensation during cell cycle (genes available for expression)

heterochromatin

chromatin that remains highly condensed throughout cell cycle, either lacks genes or contains repressed genes, found in telomeres, centromeres, Y chromosome, inactive X chromosome

histones

positively charged proteins that closely associate with DNA to form chromosomes

nucleosomes

basic unit of chromatin consisting of four pairs of histone molecules rapped by 2 turns of DNA (146 bps)

What suggested that one strand of DNA could be a template?

the complementary nature

conservative replication

entire double-stranded DNA molecule serves as a template for a whole new double-stranded DNA molecule, original DNA molecule is fully conserved during replication

dispersive replication

both parental strands break down and serve as templates for the synthesis of new DNA fragments, which then reassemble into two complete DNA molecules; each resulting DNA molecule contains interspersed fragments of old and new DNA

Semiconservative replication

two parental strands of DNA separate and each serves as a template for the synthesis of a new strand, resulting DNA molecules consist of one old strand and one new strand

basics/outcome of meselson-stahl experiment

they tested the different models of dna rep, used different weighted markers that marked the DNA, results showed semi conservative is right way

What is the origin of replication?

site where DNA replication begins, recognized/bound by certain proteins at onset of replication, bacterial chromosomes have one origin, eukaryotic have many

replication bubble

area of DNA that is unwinding and undergoing replication

replication fork

places where the double stranded DNA molecule is separated into two single strands to serve as replication templates

helicases

enzymes that unwind double-stranded DNA by breaking hydrogen bonds between bases of the two DNA strands, necessary because DNA replication requires a single-stranded template

single-strand binding proteins

proteins that bind to single stranded DNA during replication, to prevent formation of secondary structures that would interfere with replication

topoisomerases

enzymes that control the amount of DNA supercoiling by adding or removing rotations in DNA by temporarily breaking nucleotide strands, to reduce strain that builds up ahead of the replication fork due to unwinding

What is the order of things in unwinding DNA?

helicase binds to lagging strand template at each replication fork and moves along 5-3’, breaks hydrogen bonds and moving along rep fork, SSBP stablize single stranded DNA, DNA gyrase relieves strain ahead of replication fork

primase

enzyme that synthesizes a short stretch of RNA (a primer) complementary to a DNA template, to provide a 3’ OH group for DNA polymerase to attach DNA nucleotides to

DNA polymerases

enzymes that synthesize DNA by adding one complementary nucleotide at a time to the 3’ end of a growing strand

What direction does DNA synthesis occur in?

5’ to 3’

Order of nucleotide polymerization

new DNA is synthesized from dNTPs, the 3’ OH group of last nucleotide on strand attacks 5’ phosphate group of incoming dNTP, two phosphates are cleaved off, a phosphodiester bond forms between the two nucleotides

continuous replication

replication of the leading strand of DNA is in the same direction as unwinding, allows new nucleotides to be added continuously to 3’ end of new strand as the template is exposed

discontinuous replication

replication of the lagging strand of DNA in the direction opposite that of unwinding, so the DNA is synthesized in short stretches (okazaki fragments)

dna ligase

enzyme that catalyzes the formation of a phosphodiester bond between adjacent 3’ OH and 5’ phosphate groups

What are some complexities for DNA replication in eukarotes?

large genomes, nucleosomes which impede replication machinery, linear chromosomes which give an end replication problem

How is large genomes solved?

using many origins of replication

How is the issue of nucleosomes solved?

chromatin remodeling, where histones are relocated to allow passage of replication machinery, and they are immediately reassociated with new DNA

How is the end replication problem solved?

by protecting the ends of chromosomes with telomeres which can be elongated by the telomerase enzyme