Chapter 2Chapter 2

An Introduction to Genes and Genomes

Introduction to Molecular Biology

Prokaryotic Cell Structure

Prokaryotic Cell Eukaryotic Cell

Eukaryotic Cell StructureEukaryotic Cell Structure

Eukaryotic Cell StructureEukaryotic Cell Structure

Animal Cell Plant Cell

Let’s in on a cell!

DNA Zoom Interactive

DNA Discovery DNA Discovery (visit DNAi.org)(visit DNAi.org)

Miescher – identified a nuclear substance he called nuclein Griffith – performed the first transformation Avery, McCarty, and Macleod – identified Griffith’s

transforming factor as DNA Chargaff – proved that the percentage of the DNA bases

adenine always equaled thymine and guanine always equaled cytosine

Wilkins, Franklin, Watson & Crick – demonstrated the structure of DNA

Structure of DNAStructure of DNA

• Deoxyribose Sugar

• Phosphate• Nitrogen Base

Purines – double ring

Pyrimidines – single ring

Structure of DNAStructure of DNA

Structure of DNA

Nucleic Acid Overview

Structure of DNA

DNA ReplicationDNA Replication

When DNA makes an exact copy of itself

DNA ReplicationDNA Replication

The first step in DNA

DNA ReplicationDNA Replication

replication is for the enzyme, helicase, to unzip the double stranded DNA molucule.

DNA ReplicationDNA Replication

Proteins hold the two strands apart.An RNA primer lays down on each

strand of DNA.

DNA polymerase extends the primer by adding complementary nucleotides.

DNA polymerase can only extend in the 5’ → 3’ direction

DNA ReplicationDNA Replication

DNA ReplicationDNA Replication

Leading strand follows helicase. Lagging strand must wait for replication fork to

open and therefore forms discontinous Okazaki fragments.

Ligase seals the nicks in the DNA backbone between the Okazaki fragments. helicase

Let’s put it all togetherLet’s put it all together

Click on the animation below.Select the button for the “whole

picture”.

DNA Replication Animation

TranscriptionTranscription

Making an RNA copy from a DNA template

RNA polymerase

RNA StructureRNA Structure

Uracil instead of thymine

Ribose sugar instead of deoxyribose sugar

Single strandedCan leave the nucleus

RNA StructureRNA StructuremRNA – RNA copy of DNA that carries

genetic information from the nucleus to the ribosomes

rRNA – makes up the ribosomestRNA – carries amino acids to ribosomes

for protein synthesis

Transcription

RNA polymerase binds to a promoter region on double stranded DNA and unzips the double helix.

Transcription

Free RNA nucleotides pair with the complementary DNA of the template strand

Transcription

RNA is processed Introns are spliced out 7 methyl guanosine cap Poly-A tail

Transcription

mRNA leaves the nucleus and travels to the ribosomes in the cytoplasm

ribosome

nucleus

Let’s put it all together

Transcription Animation

Practice

Central Dogma of Molecular Biology

Click to see Video

Animation

Translation

Making protein from mRNA

Translation

Important Definitions A codon is composed of

3 RNA nucleotides Each codon codes for

one amino acid Protein does the work in

a cell

Translation

Translation

First Base Second Base

U C A G

U

U

C

A

G

phenylalanine

serine

tyrosine

cysteine

phenylalanine

serine

tyrosine

cysteine

Leucine

serine

(stop)

(stop)

Leucine

serine

(stop)

tryptophan

C

U

C

A

G

leucine

proline

histidine

arginine

leucine

proline

histidine

arginine

leucine

proline

glutamine

arginine

leucine

proline

glutamine

arginine

A

U

C

A

G

isoleucine

threonine

asparagine

serine

isoleucine

threonine

asparagine

serine

isoleucine

threonine

lysine

arginine

met (start)

threonine

lysine

arginine

G

U

C

A

G

valine

alanine

apartic acid

glycine

valine

alanine

apartic acid

glycine

valine

alanine

glutamic acid

glycine

valine

alanine

glutamic acid

glycine

Third Base

Translation

Translation

Translation

Translation

• Asparagine, Serine, Methionine

• Tryptophan, Glycine, Lysine

• Proline, Leucine, Serine• Aspartic acid, Histidine, Threonine

Translation

Always begins at a start codon and ends at a stop codon.

The region between the start and stop codons is called the open reading frame (ORF)

Practice

Click on the animation to transcribe and translate a gene.

Click to see animation

Translation Initiation

mRNA attaches to the small subunit of a ribosome

tRNA anticodon pairs with mRNA start codon

Large ribosomal subunit binds and translation is initiated

tRNA anticodon

amino acid

Translation Elongation

Anticodon of tRNA carrying next amino acid binds to codon on mRNA

A peptide bond joins the amino acids and the first tRNA is released.

Translation Termination

Amino acid chain continues until a stop codon is read. The amino acid chain is released and all of the translation machinery is recycled to translate another protein.

Let’s put it all together

Click on the animation below

Translation Video

Translation Animation

Let’s put it all together

5’-GATCTGAATCGCTATGGC-3’

3’-CTAGACTTAGCGATACCG-5’

mRNA 5’-GAUCUGAAUCGCUAUGGC-3’

CUAGACUUAGCGAUACCG Asp, Leu, Asn, Arg, Tyr, Gly

Coding:

Template:

mRNA:

tRNA:

amino acid:

Control of Gene Expression

Control of Gene Expression

Control of Gene Expression

Prokaryotes cluster genes into operons that are transcribed together to give a single mRNA molecule.

Lac Operon Promoter region allows RNA polymerase to

attach and begin transcription. Operator region is in the middle of the

promoter.

Control of Gene Expression

If a repressor protein is bound to the operator, RNA polymerase cannot pass to transcribe the genes.

Control of Gene Expression

When the inducer (lactose) binds to the repressor protein, it changes shape and falls off of the operator region.

Now RNA polymerase can pass and transcribe the genes into mRNA.

Control of Gene Expression

Let’s put it all together

Click on the animation below.

Video of lac operon

Animation of lac operon

Mutations

Mutations are changes in the DNA sequence.

Mutations can be inherited or acquired.

Mutations

Mutagens are agents that interact with DNA to cause mutations.

Examples are chemicals and radiation.

Mutations

Point mutation changes a single base Point mutations can be silent, meaning they code

for the same amino acid.

Mutations

Point mutations can also code for a structurally similar amino acid.

Mutations

Point mutations are not always harmless. If the mutation occurs on a critical amino acid in the active

site of the protein, it can be detrimental, as in the case of sickle cell anemia.

Mutations

Frameshift mutations cause a shift in the reading frame by adding or deleting nucleotides.

Mutations

An example of a deletion causing a premature stop codon.

Mutations