Lecture 9

Molecular Genetics

DNA Replication, Transcription & Translation

____________ Genomes

• Prokaryotic genomes are made of DNA.

• Prokaryotic chromosomes can be circular or linear.

• Genome floats freely within cytoplasm • Where is DNA found in prokaryotes?

– ______________ .

– ______________

Transmission electron micrograph of E. coli O157:H7 showing flagella. (Courtesy of the CDC)

____________ Genomes

• The genomes of eukaryotic organisms are made of DNA.

• Eukaryotic genomes frequently include several to many linear chromosomes sequestered within membrane-bound nucleus

(How many do we have?).

• Where is DNA found in eukaryotes?

– Nuclear DNA – Extranuclear DNA

(Where is extranuclear DNA?)

Human epithelial cells stained with DAPI (blue, to show the nucleus) and phallotoxin (red, to show F actin in the cell body) Courtesy of RL Alford, PhD

Nucleotides

and

Nucleic Acids

Organic Molecules –

Nucleic Acids

Image:

www.geneticengineering.org/.../DNA.htm

Nucleic Acids - DNA

DNA is a double stranded molecule, analogous to a ladder.

The “ladder” = • two deoxyribose phosphate chains form the “

side rails

” • base pairs, linked by hydrogen bonds, form the “

rungs”

.

Purine Bases

(double ring) Adenine & Guanine

Pyrimidine Bases

(single ring) Cytosine & Thymine Image:

www.biologycorner.com/bio1/DNA.html

Image:

whyfiles.org/034clone/dna.html

Nucleic Acid Function

Replication

Transcription Translation

Replication

Copying the genetic material is

REPLICATION

.

Replication occurs prior to ________________, because the new, daughter cell will also need a complete copy of cellular DNA.

Replication

DNA Replication

• __________ a double-stranded DNA molecule.

• Each DNA strand holds the same genetic information, so both strands can serve as templates for the reproduction of opposite strand.

• The _________ or __________ strand is preserved and the ______ or ___________ strand is assembled from nucleotides • This is called ___________________ replication. • The resulting double-stranded DNA molecules are identical.

Replication

DNA Replication

• In a cell, DNA replication must happen before cell division. • _________ replicate their DNA throughout the interval between cell divisions. • In ____________, timings are highly regulated.

Fluoresced E. coli colony:

http://ibis.inrialpes.fr/article.php3?id_article=886 Root tip: http://district.bluegrass.kctcs.edu/billd.snyder/sharedfiles/biowebsite/BiologyLabs/BIO137/137Lab2/Lab2MitosisSlides.html

______________ DNA Replication: Replication “Bubbles” • Origin of replication (“bubbles”): beginning of replication • Replication fork: ‘Y’-shaped region where new strands of DNA are elongating Replication

_______________ DNA Replication:

One Origin

• Prokaryotic DNA is arranged in a circular shape, and there is only one replication origin when replication starts. • Despite these differences, the underlying process of replication is the same for both prokaryotic and eukaryotic DNA. Replication

How Do Nucleotides Put Themselves Together Into Nucleic Acids?

• An anabolic polymerization process.

- Anabolic

or Anabolism is….? _____________________________

- Polymerization

= taking monomers and putting them together into polymers (large molecules composed of many monomers).

• Polymerization requires ___________ (building blocks) and ________ .

- Triphosphate deoxyribonucleotides provide both.

- These building blocks of DNA bring their own energy for polymerization.

Replication

DNA Replication:

__________ Nature of DNA

• Sugar/phosphate backbone runs in opposite directions.

• One strand runs 5’ to 3’, while the other runs 3’ to 5’.

• DNA polymerase, enzyme that facilitates addition of nucleotides in building the new DNA strand, • C

an only adds nucleotides at the free 3’ end

Why is this important?

Replication

DNA Replication:

Leading & Lagging Strand

________ Strand

Synthesis toward the replication fork (only the 3’ to 5’ of the master strand).

________ Strand

Synthesis away from the replication fork (Okazaki fragments); joined by DNA ligase.

Replication

DNA Replication

VIDEO: http://207.207.4.198/pub/flash/24/24.html

Reminder…Why is the DNA copied?

Replication occurs prior to cell division , because the new, daughter cell will also need a complete copy of cellular DNA.

Replication

Replication Mistakes: _________ of Genes • Change in the nucleotide base sequence of a genome; rare.

• Almost always deleterious (bad).

• Rarely lead to a protein having a novel property that improves ability of organism and its descendents to survive and reproduce.

Nucleic Acid Function

Replication Transcription Translation

Replication & Transcription

MAKING DNA Making a copy of the genetic material = ____________.

When you think “replication” think “duplication” MAKING RNA Transferring the genetic code (DNA) into RNA = ________________. Think of a medical transcriptionist. (S)he is just copying the physicians words into another format.

Nucleic Acids - RNA

RNA is typically a single stranded molecule

Purine Bases

(double ring) Adenine & Guanine

Pyrimidine Bases

(single ring) Cytosine & Uracil

Base Pairs

(purine always pairs with pyrimidine)

__________ + _________ __________ + _________ Image:

www.biologycorner.com/bio1/DNA.html

Transcription

Process by which a DNA sequence is copied to produce a complementary RNA. In other words, it is the transfer of genetic information from DNA into RNA. Like replication, but we are making RNA.

Beginning of the process that ultimately leads to the translation of the genetic code (via mRNA) into a peptide or protein. Transcription

Types of RNA Genetic information copied from DNA is transferred to 3 types __________ RNA: mRNA

Copy of information in DNA that is

__________ RNA: rRNA

Most of the RNA in cells is associated the protein factories of the cells.

,

___________ RNA: tRNA

Brings the amino acid to the ribosome Transcription & Translation

Nucleic Acid Function

Replication Transcription Translation

Replication, Transcription, Translation MAKING DNA Making a copy of the genetic material = Replication When you think “replication” think “duplication”

Where does replication occur in prokaryotes? Eukaryotes?

MAKING RNA Transferring genetic code (DNA) to RNA = Transcription Think of a medical transcriptionist. (S)he is just copying the physicians words into another format.

Where does transcription occur in prokaryotes? Eukaryotes?

MAKING PROTEINS Making proteins = ______________.

Think of how translation relates to languages.

The translation of cell biology translates DNA information into proteins.

Translation _____________

(which contain rRNA)

make proteins from the messages encoded in mRNA.

– Three nucleotide groups called _______ encode one amino acid. – This is the genetic code.

Nearly completed protein Beginning of protein mRNA 3'

Adapted from: L. Stryer. Biochemistry, 3rd ed..

Translation

Translation: The ______________ • The genetic instructions for a polypeptide chain are ‘written’ in the DNA as a series of 3-nucleotide ‘words’ • ______ on mRNA • ___________ on tRNA • ‘U’ (uracil) replaces ‘T’ in RNA •

Where does translation occur in prokaryotes? Eukaryotes?

http://learn.genetics.utah.edu/units/basics/transcribe/ http://207.207.4.198/pub/flash/26/26.html

Transcription & Translation: Overview Eukaryotic Cell

______________

Synthesis of RNA under the direction of DNA (mRNA)

______________

Actual synthesis of a polypeptide (protein) under the direction of mRNA

Transcription & Translation

Replication, Transcription & Translation: Overview