Chapter 16.0: the molecule basis of inheritance

what makes up a nucleoside

base+ sugar with no phosphate group

whos rules do DNA base pairing follow

chargoff’s rules

origin of replication

where replication begins and where two DNA strands are separated and open a replication bubble

eukaryotes chromosomes have how many origins of replication

can have hundreds to thousands of origins of replication

prokaryotic chromosomes have how many origins of replication

prokaryotic chromosomes are circular and have only one origin of replication

what direction does replication occur

occurs in both directions from 5’ to 3’ on each strand

what is at the end of each replication bubble

a replication fork, a y-shaped region where the parental DNA are being unwound

helicases

enzymes that untwist the double helix at the replication forms

topoisomerase

relieves the strain of twisting of the double helix by breaking, swiveling and rejoining DNA strands

single- strand binding proteins

bind to an stabilize single stranded DNA that has been separated and unwound

DNA polymerases

enzymes that produce a new DNA strand

what does DNA polymerases require

a primer

what does the primer do

the initial nucleotide chain that is made of 5-10 nucleotides

primase

synthesizes the primer by adding RNA nucleotides one at a time pairs the bases with the parental/template DNA strand

where does the new DNA strand being forming

begins forming from the 3’ end of the RNA primer

DNA polymerase III

the enzyme that initially adds a DNA nucleotide onto the 3’ end of the RNA primer and then continues to add DNA nucleotide to extend the strand

what is the different in rate of elongation between bacteria and human cells

human cells is about 50 per second and bacteria is about 500 nucleotides

how do monomers add to the DNA strands

via dehydration reactions

what supplies DNA polymerase with the energy to form the phosphodiester bond

hydrolysis of pyrophosphate

what affects replication

the antiparallel structure of the double helix

what direction must the new DNA strand elongate

5’ → 3’ direction

the leading strand

the DNA polymerase synthesizes this strand continuously towards the replication fork and as the replication bubble opens up the leading strand continues to elongate towards the edge of the bubble

what direction does the leading strand go

5’ → 3’ direction towards the replication bubble on both strands going antiparallel

the lagging strand

lagging behind the leading strand, the DNA polymerase works in the direction away from the replication fork

okazaki fragments

what makes up the lagging strand, a series of segments that are eventually joined together by a bond

Helicase

unwinds the parental double helix at replication forks

single strand binding protein

binds to and stabilizes single stranded DNA until it is used as a template

topoisomerase

relieves overwinding strain ahead of replication forks by breaking, swiveling and rejoining DNA strand

primase

synthesizes an RNA primer at 5’ end of leading strand and at 5’ end of each Okazaki fragment of lagging strand

DNA polymerase III

using parental DNA as a template, synthesizes new DNA strand by adding nucleotides to and RNA primer or a pre-existing DNA strand

DNA polymerase I

removes RNA nucleotides of primer from 5’ end and replaces then with DNA nucleotides added to 3’ end of adjacent fragment

DNA ligase

joins okazaki fragments of lagging strand, on leading strand, joins 3’ end of DNA that replaces primer to rest of leading strand DNA

what bond attaches the 3’ end of the okazaki fragment with the 5’ end of the adjacent fragment

phosphodiester bonds

describe the process of DNA ligation

the primer is replaced with DNA nucleotides in the RNA primer and replaces then with the DNA equivalent by adding DNA nucelotides onto the 3’ end of an existing DNA nucelotide. then the 3’ end of the okazaki fragment is attached to the 5’ end of the adjascent fragment by a phosphodiester bond

what makes up the DNA replication complex

the proteins that participate in DNA replication

“DNA replication machine”

the DNA replication complex, may be stationary during the replication process

what does DNA polymerases do to newly made DNA

proofreads the DNA and replaces any incorrect nucleotides

repair enzymes

replaces incorrectly paired nucleotides that the DNA polymerase may have missed

what occurs during nucleotide excision repair

a nuclease cuts out damaged stretches of DNA and polymerase fills in the missing nucelotides and DNA ligase links the repaired back to the DNA backbone

what is true about sequence changes

they can be permanent and passed down through generations if they occur in the gamete

what is responsible for genetic variation and the appearance of new species

mutation in the gametes

xeroderma pigmentosum

caused by inherited defect that makes people very sensitive to sunlight and can easily cause skin cancer

what is an issue with repeated rounds of replication

the DNA molecules become short with uneven ends

what is unique about prokaryotes chromosomes

they have circular chromosomes

how do eukaryotic cells overcome these problems

they have special nucleotide sequences at their ends called telomeres

telomeres

consist of multiple repetitions of one short nucleotide sequences like TTAGGG, and they do not prevent the shortening of DNA molecules during replication but they do postpone the erosion of genes near the ends of DNA molecules

what do telomeres do to somatic cells

they might protect cells from becoming cancerous growth by limiting the number of cell divisions that they can have