DNA, RNA, and Protein Synthesis - PowerPoint Presentation

Slide1

DNA, RNA, and Protein Synthesis

Chapters 16 and 17Slide2

Before the end of the semester we will be covering…

Historical DNA experiments

Structure of DNA/RNA

DNA Replication

Protein Synthesis (Transcription and Translation)

Mutations

Gene Expression (if time)

No more labs this semester!

Your final will be comprehensive

 Both multiple choice and short answer…more info to come!Slide3

Important Historical Experiments

In

the 1940s

little was understood about inheritance and how it worked.

It

was believed the genetic material was either DNA or protein

.

It was understood that chromosomes are made of both DNA and protein

Initial experiments suggested it was

protein…little was understood about DNA’s structure or function (proteins were identified as being more complex)Slide4

Avery, McLeod,

McCarty

1944

goal was to identify if inherited substance was either DNA, RNA, or protein

used chemicals and bacteria that only allowed one of the above to be active at a time

Results determined that the transforming agent was DNA

Scientific community still skepticalSlide5

Hershey and Chase 1952

used bacteriophages to confirm DNA is the genetic material

bacteriophages were tagged with radioactive isotopes (DNA--P; protein--S)

it was shown that the DNA was able to “infect” the bacteriophages, not the protein by tracking the radioactivitySlide6

Watson and

Crick 1953

discovered

the shape of

DNA molecule

was a double helix

using pictures of the molecule, they built a model

sugar/phosphate backbone

nitrogen bases in the interior

strands are

antiparallel

helix uniform in diameter (base-pairing rules)Slide7

Wilkins and

Franklin 1953

Franklin

used x-ray diffraction to photograph DNA (her pictures were used by Watson and Crick)

Wilkins was working closely with Franklin in her lab and allegedly showed Watson and Crick the

photograph that helped them build their model

Watson,

Wilkins,

and Crick were awarded the Nobel Prize for science in 1962.

Rosalind

Franklin died

in 1958 of cancer and was never given a Nobel Prize.Slide8

Using the original papers published in

Nature

in 1953, identify the characteristics of a DNA molecule.

What important characteristics did they (Watson, Wilkins, Crick, and Franklin) discover? List/highlight as many as you can.Slide9

Deoxyribonucleic Acid (DNA)

Classified as a

nucleic acid

(biological molecule)

Genetic material

organisms inherit from their parents

Copied prior to cell division (mitosis/meiosis)

Shape of a

double helix

Made up of

nucleotides

(building blocks)

5-carbon sugar (deoxyribose), phosphate, nitrogen baseSlide10

Base-Pairing Rules:

A



T

C

G

Directionality

Complementary strands

Antiparallel

:

each strand runs in an opposite direction

Designated 5’ and 3’ ends (carbon on sugar)

Two types of basesPurines: two carbon ringsGuanine, AdeninePyrimidines: one carbon ringCytosine, Thymine, UracilSlide11

Ribonucleic Acid (RNA)

mRNA (messenger RNA)—

instructions (from DNA) for making protein

tRNA (transfer RNA)–

carries amino acids

rRNA(ribosomal RNA)—

makes up ribosomes

5-carbon sugar (ribose)

Single stranded (one gene)

Uracil instead of thymine

A

USlide12

Both RNA and DNA…

Have adenine, cytosine, and guanine

Made of nucleotides

Sugar and phosphate backbone

Nitrogen bases perpendicular to backbone

Held together by hydrogen bondsSlide13

Biochemical Gymnastics: DNA Replication

Occurs during S-phase of

Interphase

in the cell cycle

Semi-conservative process

. Each new strand of DNA produced is made of

one parental

and

one new strand

(described by Watson and Crick)

Each strand serves as a template for the new strand

In prokaryotes DNA is circularIn eukaryotes DNA is linear Slide14

DNA Replication

(Overview)

Begins at the origin of replication (specific sequences of DNA nucleotides)

Proteins recognize this sequence and attach to the DNA and separate the two strands creating a “bubble”

At either end of this “bubble” is the

replication fork

Replication then proceeds in both directions from the origin until both strands are copied.

In prokaryotes replication starts in one spot, in eukaryotes multiple spotsSlide15

The Players.

Helicase

: enzyme that unwinds and unzips the helix at the replication forks.

Single-strand Binding Protein (SSBP’s)

: binds to unpaired DNA strand to keep them from re-pairing

Topoisomerase

: enzyme that relieves tension ahead of the replication fork (from untwisting of strand)

Primase

: enzyme that synthesizes the RNA primer for replication

DNA Polymerase

: several enzymes that catalyze the synthesis of new DNA (in eukaryotes there are 11 total); also checks for errors

Ligase: links new fragmented DNA segments togetherSlide16

Replication only occurs in the 5’ to 3’ direction

Nucleotides added only to 3’ end of molecule…

This is problematic for one side of the DNA molecule

Leading strand

: continuous strand

Single RNA primer

Lagging strand

: discontinuous in fragments (Okazaki fragments)

multiple RNA primersSlide17

The steps…

1. Origin of replication is located

2. Bubble forms in DNA helix by

Helicase

3.

Primase

synthesizes primer to begin replication

Need RNA primer to have something to add nucleotides to.

4. DNA Nucleotides are added by DNA polymerase to primer to begin new strand

5. Replication proceeds in the 5’ to 3’ direction on both sides of the molecule

Leading and lagging strands

6. Replication continues until the entire molecule is copied

http://highered.mheducation.com/sites/0035456775/student_view0/chapter12/dna_replication.html http://www.dnalc.org/resources/3d/04-mechanism-of-replication-advanced.html Slide18

Ending Replication…

After every round of replication some of the DNA molecule is lost due to polymerase not being able to replicate it.

To avoid excess loss of DNA, the ends of eukaryotic chromosomes have

telomeres

(long repeating sequences)

Excess DNA nucleotides (no genetic info)

Acts as a buffer to actual genes (does shorten over time—thought to be evidence of aging)Slide19

Protein Synthesis (gene expression)

Chapter 18Slide20

Gene Expression

: process by which DNA directs the synthesis of proteins

occurs in two parts:

Transcription and Translation

this process dictates the presence of specific traits (genotype/phenotype)

occurs in all organisms

Watson and Crick describes this as the “central dogma” (

DNA



RNA



Protein)Slide21

Transcription

synthesis of RNA (mRNA) using DNA as a

template (protein instructions)

occurs in nucleus (eukaryotes) or cytoplasm (prokaryotes)

Prokaryotes can begin translation before transcription is finished

Eukaryotes have an extra step during transcription before translation can beginSlide22

DNA is a template strand, which is used to produce mRNA instructions (for protein)

mRNA is complementary to DNA

uses different nucleotides (

uracil

)

RNA

polymerase

unzips DNA and joins complementary RNA nucleotides to copy instructions

reads 5’ to

3’ , no

primer needed

promoter: DNA sequence where RNA polymerase attaches and initiates transcriptionhttp://www.dnalc.org/resources/3d/13- transcription-advanced.html Slide23

3 Stages

Initiation

RNA polymerase joins to the promoter and begins to unwind helix

helped by transcription factors (proteins), creates a “transcription-initiation complex”

Elongation

RNA polymerase unwinds/untwist 10-20 nucleotides at a time

nucleotides added to 3’ end

as mRNA is built, the molecule peels away from DNA and the double helix reforms

Termination

in prokaryotes there is a terminator sequence (stop signal)

eukaryotes transcribe a specific sequence to stop transcription (creates pre-mRNA)Slide24

RNA

Modifications

(eukaryotes only)

RNA processing

: enzymes in the nucleus modify pre-mRNA

To help protect from

degradation

5’ cap (modified G sequence)

3’ (poly-A tail)

RNA splicing

: removal of large portions of the RNA molecule (cut and paste)

eukaryotes have long stretches of non-coding DNA interspersed with coding segmentsintrons: non-coding segmentsexons: coding segments eventually expressedSlide25

RNA Splicing…

introns

are removed and

exons

are joined

together

snRNPs

: join together to form a spliceosome

Once finished, completed mRNA leaves nucleus to begin translationSlide26

Translation

synthesis of

a polypeptide

using

mRNA as instructions

occurs on

ribosomes

(

rRNA

) in cytoplasm

tRNA

: transfers amino acids to growing proteineach associated with a particular amino acidanticodon: complementary RNA sequence to mRNA Slide27

instructions for producing a protein uses three letters on mRNA (triplet code)

codon

: mRNA triplet (3 nucleotides)

methionine

is “start”

“stop”

codons

UAA, UAG, UGASlide28

3 stages

Initiation

mRNA,

tRNA

, and ribosome start with amino acid

methionine

(initiator

tRNA

)

“translation initiation complex”

Elongation

amino acid added to chain via sites on ribosome (A-P-E)“elongation factors” help process; reads 5-3’requires energyTerminationstop codons

end synthesis, codes for “release factor”release factors bind and protein is released via hydrolysisProtein is then folded into appropriate shape with help of chaperonin proteinshttp://www.dnalc.org/resources/3d/16-translation-advanced.html Slide29

Oops!

Mutation

: change to genetic information

Ultimate source of new genes

May be spontaneous or result from

mutagens

Point mutations

: change in single

nucleotide (substitution)

silent

: change doesn’t alter amino acid sequence

missense: changes one amino acid into another (minor changes)nonsense: change codon for amino acid into a stop codon (premature end to translation)Frameshift

mutation: add/lose nucleotides resulting in change to reading frame of codons (not multiples of 3)Insertion or Deletionhttp://www.bozemanscience.com/mutations/