Chapter 11 biology

nucleotides

subunits DNA is comprised of

three parts of DNA

central deoxribose sugar

phosphate group

organic, nitrogen containing base

larger bases with double ring structure

purines

larger base purines

Adenin and Guanine

smaller bases with single rings

pyrimidines

small bases- pyrimidines

cytosine and thymine

Edwin Chargaff

dna molecules always had equal amounts of purines and pyrimidines

Chargaffs rule

Dna had a regular structure- A=T and C=G

Rosalind Franklin

using X-ray diffraction revealed that DNA had a regular structure that was shaped like a helix

Discover of the double helix

Francis Crick and James Watson

Double helix

two strands of sugar and phosphate groups connected in the middle by their bases

Double helix structure

bulky purine bases pair with slender pyrimidine bases

how are the two strands of DNA that form the double helix DNA molecule related

they are complementary to each other

how are each chain of DNA perceived

They are a mirror of the other

what does the complementarity of the DNA do?

it makes it possible for DNA to copy itself in preparation for cell division

DNA replication

the double helix assembles a new complementary chain along each single strand.

What happens to the original duplex

the sequence of the original duplex is conserved after one round of replication, but the duplex itself is not

what happens to the parent duplex

it becomes another, daughter dna duplex

Daughter Dna

composed of one original strand and one new strand

the process of DNA replication involves several enzymes

Helicase, dna polymerase, dna ligase, dna repari

helicase

unwinds the DNA double helix to expose the signal strands- one free 3 and one free 5

helicase- replication fork

a primer must first be added to give a place for DNA polymerase to start

DNA polymerase

adds complementary nucleotides to each strand of dna

DNA polymerase- addition to nucleotide

can only add nucleotides to the 3’ end of an existing strand

leading strand

new daughter strand that is added during dna polymerase

DNA ligase

Seals fragments of DNA togeteher

DNA sealing during DNA ligase

the primer must be removed and the DNA fragments must be sealed together

continuous strands

during DNA ligase- the ends of the fragments join together in order to form these strands

DNA ligase- what becomes a problem and why?

the other template having a free 5’ end because new nucleotides can only be added to the 3’ end of an existing strand

during dna ligase, the second daughter…

the second daughter strand assembled in segments, each one beginning with a primer

lagging strand

during DNA ligase, the segments are joined together to form

DNA repair

involves comparing the two strands to each other to check for mistakes

Mutation

a change in a cell’s genetic message

mutation can result from..

errors in replication or be caused by chemicals or radiation

mutation can involve

changes, additions or deletions to nucleotides

mutations are

the ultimate source of variation and the raw material of evolution (rare)

mutations can alter…

the genetic message and affect protein

most mutation are

detrminetlam

most mutations occur randomly…

in a cells DNA

what does the effect of mutation depend on?

depends on the identity of the cell, where it occurs

mutation in germ lines

will be passed on to future generations and are important for evolutionary changem

mutations in somatic cells

not passed to future generations, but passed to all other somatic cells derived from it

point mutations

mutations that arlter the sequence of only one or a few bases pairs

point mutations- alternators

base substation changes the identity of a base

insertion- adds base

deletion- removes base

frameshift mutation resutls- if the insertion or deletion throws the reading frame of the gene message out of register 

mutagens- chemicals that cause mutation

frameshift mutation can be

determinedly because the final protein intended by the message may be altered or not mademu

mutagens can

be linked to cancer (chemicals in cigarettes smoke cause cancer)

all evolutionary change begins with

mutation

mutation and recombination

provide the raw material for evolution

CRISPR

gene editing- clustered regularly interspersed short palindromic repeats

CRISPR- researchers discovered an unusual DNA sequence in a bacterial gene composed of

several dozen DNA bases

followed by the same sequence in reverse

then a 30 base “spacer”

30 base spacer

the RNA enzyme complex cuts up the DNA sequences specific baby the 30 base spacers

30 base spacer vs viral DNA

uses the RNA enzyme to protect themselves from viral DNA

researchers now substitute any 30 base sequence fro the spacer in order to..

target a gene for modification or destruction (CRISPR)

The RNA transcript of the sequence forms

loops and can bind to a DNA cutting enzyme

after a gene is cut with CRISPR

the cell repairs the gap

what does the gene on the homologous chromosome normally serve as>

a template for the repair

How will the cell be inserted into the gap?

if the cell is flooded with many copies of another DNA sequence

How is the gene edited?

The gene can be edited to contain a DNA sequence of the investigators choosing

CRISPR- how can gene editing show promise for treating human diseases

1. targeting genes that also humans to be infected with HIV which could possible cure aids

2. removing RNA viruses from pig organ cells so they can be used for transplants

3. correcting disease-causing mutations in embryos and adults (sickle cell disease)

4. treating cancer through gene therapy

Genes

blocks that store the information containing DNA

The Central Dogma

Transcription to Translation

Transcription

genetic information passes from the genes to an RNA copy of the gene

Translation

RNA copy directs the sequential assembly of a chain of amino acids

Translation forms

a polypeptide which will become a protein

Gene expression

the combination of transcription and translation

Gene expression uses

the information in DNA to direct the production of particular proteins

Transcription steps

1. the DNA stews genetic information safely in the nucleus where it never leaves

2. instructions are copies from the DNA into messages comprised of ENA

   1. these messages are sent out into then cell to direct the assembly of proteins

Messenger RNA (mRNA)

an RNA copy of a gene used in the cell to produce polypeptide

mRNA

conveys the instructions from protein

RNA polymerase

protein

RNA polymerase (protein)

produces the mRNA copy of DNA during transciption

RNA polymerase (protein) steps

1. first binds to one strand of DNA at a site called the promoter adnd then moves down the DNA molecule

2. it pairs cytosine with guanine and adenine with uracil

Uracil replaces what

thymine in RNA

Transciption to Translation

after transcription, the mRNA is transported from the nucleus where it was made to the site of protein synthesis

protein synthesis

cell structures called ribosomes in the cytoplasm

Translation

the process by which ribosomes convert the information in mRNA into proteins

Ribosomes

help translate the information the mRNA contains from the language of mRNA to the language of proteinsla

language of proteins

amino acidslan

language of mRNA

nitrogenous bases

Codons (64)

the three bases that the mRNA information reads

the four bases of mRNA

ACGU

three stop codons

UAA, UAG, UGA

start codon

the ribosomes starting point on the mRNA strand

Translation begins

when mRNA binds to a ribosome

ribosome reaches a stop codon

the mRNA and the completed amino acid chain both separate from the ribosome

Translation ending

The ribosome complex falls apart and the newly made protein is released into the cell

the prokaryotic gene

is an uninterrupted stretch of DNA nucleotides

in eukaryotes

the coding portions of the DNA nucleotide sequence are interrupted by noncoding sections of DNA

exons

the coding portions

introns

the noncoding portions

eukaryotic cell produces

a primary RNA transcript of the entire cell

the primary transcript is process in

the nucleus

human exons

spliced together in different ways

using different combinations of the same exons

different proteins can be created

Thomas Malthus essay on

the principle of population

Thomas malthus- while human populations tend to increase geometrically

the capacity for humans to feed this population only grows arithmetically

Darwin expanded Malthus’ view

to include every organism

Darwin- all organisms

have the capacity to over reproduce

darwin- only a limited number of these offspring

survive and produce the next generation

Survival of the fittest

Darwin- organism whose characteristics are best suited to their particular environment survive more often and lead more offspring