Molecular Basis of Inheritance Flashcards by Kevin Avelino

What technique was used to study molecular structure?

X-Ray Crystalography

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Franklin’s X-Ray Crystallographic images of DNA enabled Watson to deduce that DNA was

helical

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X-Ray images also enabled Watson to deduce the

width of the helix and the spacing of the nitrogenous bases

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Pattern in the photo suggested that the DNA molecule was made up of _____ , forming a ______

Two Strands

Double Helix

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Watson and Crick built models of a double helix to conform to the _____ and _____ of DNA

X-Rays

Chemistry

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Franklin had concluded that there were two outer ______, with the Nitrogenous ______

Sugar-Phosphate backbones

Nitrogenous bases paired in the molecule’s interior

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Watson built a model in which the backbones were ____

antiparallel (their subunits run in opposite directions)

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Pairing a ___ with a ____ resulted in a uniform width consistent with the X-Ray Data

Purine

Pyrimidine

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Purine + Purine =

Too wide

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Pyrimidine + Pyrimidine =

Too Narrow

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DNA Base Parings

Adenine - Thymine

Guanine - Cytosine

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Watson - Crick Model explains

Chargaff’s Rules

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Chargaffs Rules

In any organism, the amount of A=T will be equal to the amount of G=C

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Since the two strands of DNA are complementary, ____

each strand acts as a template for building a new strand in replication

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In DNA replication, the parent molecule unwinds, and two new daughter strands are built based on ____

base-pairing rules

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Semiconservative Model

Predicts that when a double helix replicates, each daughter molecule will have one old strand (derived or “conserved” from the parent molecular) and one newly made strand

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Conservative Model

Two parent strands rejoin

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Dispersive Model

Each strand is a mix of old and new

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Replication begins at particular sites called _____

Origins of Replication

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What happens at the origin of Replication?

Two DNA strands are separated, opening up a replication “bubble”

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A eukaryotic chromosome may have _____ origins of replications

hundreds or even thousands

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Replication proceeds in ____ , until the entire molecule is copied

both directions from each origin

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At the end of each replication bubble is a ____

replication fork, a Y-shaped region where new DNA strands are elongating

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____ are enzymes that untwist the double helix at the replication forks

Helicases

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_____ bind to and stabilize single-stranded DNA

Single-strand binding proteins

______ corrects "overwinding" ahead of replication forks by braking, swiveling, and rejoining DNA strands

Topoisomerase

DNA polymerases cannot initiate synthesis of a polynucleotide; they can only ____

add nucleotides to an existing 3' end

The initial nucleotide strand is a short ____

RNA primer

what does Primase do?

Can start a RNA chain from scratch and adds RNA nucleotides one at a time using the parental DNA as a template

The primer is _______ and the _ end serves as te starting point for the new DNA strand

short (5-10 nucleotides long) | 3'

What do DNA Polymerase do?

Catalyze the elongation of new DNA at replication fork

Most DNa polymerases require a ____ and a ____

Primer | DNA Template Strand

The rate of elongation is what in bacteria and humans?

500 nucleotides per second in bacteria and 50 per second in human cells

A ____ structure of a double helix affects replication

Anti parallel

DNa polymerases add nucleotides only to the ____ of a growing strand

Free 3' End

New DNA strand can elongate only in the ____ direction

5' to 3'

Along one template strand of DNA, the DNA polymerase synthesizes a ____

leading strand continuously, moving toward the replication fork

To elongate the other new strand, called the ____, DNA polymerase must work in the direction ___ from the replication fork

Lagging Strand | away

Lagging strand is synthesized as a series of segments called ____ , which are joied together by _____

Okazaki Fragments | DNA ligase

Okazaki Fragmet size in Eukaryotes and Prokaryotes

100-200 n in Eukaryotes and 1000-2000 in prokaryotes

Helicase Function

Unwinds 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 strands

Primase

Synthesizes an RNA primer at 5' end of leading strand, and at 5' end of each Okazaki fragment of lagging strand

DNA Poll III

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

DNA Pol I

Removes RNA nucleotides of primer from 5' end and replaces them with DNA nucleotides

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

DNA Polymerases job is to

proofread newly made DNA, replacing any incorrect nucleotide

In mismatch repair of DNA, repair enzymes

correct errors in base pairing

DNA ca be damged by

exposure to harmful chemical or physical agents such as cigarette smoke and X-Rays; it can also undergo spontaneous changes

In Nucleotide excision repair, a nuclease _____

cuts out and replaces damaged stretches of DNA

Can sequence changes become permanent?

Yes, and they can be passed on to the next genertion

Mutations due to sequence changes are the source of ____ upon which natural selection operates

Genetic Variation

The unusual replication machinery provides no way to complete the ___ , so repeated rounds of replication produce __ DNA molecules

5' Ends | Shorter

Telomeres are located where?

At the ends of eukaryotic chromosomes

What do Telomeres do?

They are like a protective cap, to ensure all genetic information is passed from one generation to next after replication. Prevents damage to end and joining with adjacent chromosomes

How many times does TTAGGG repeat in Vertebrates?

2500 Times

Average cell divides ____ , losing ____ of telomere with each division.

50-70 times | 25-200 bp

Aging driven by

Telomere shorterning

What happens when the telomere is too short?

Chromosome reaches "critial length" and can no loger replicate and cell dies (apoptosis)

Tekinerase

RNP - Reverse TRabscriptase, carries its own RNA

Telomerase; what is the strand name that is carried in Vertebrates?

CCCAAUCCC

Telomerase; Adds telomere repeat _ to 3" end of chromosomes

TTAGGG

Why is telomerase activated?

To treat aging and age related diseases

Using Telomerase _____ to treat cancer

Inhibition Cancer cells cause then to be 10-20 more active. Shorting protect cells from cancerous growth by limiting number of cell divisions

What would happen if chromosomes of germ cells became shorter in every cell cycle?

Essential genes would eventually be missing from the gametes they produce

What does the enzyme telomerase do?

Catalyzes the lengthening of telomeres in germ cells?