DNA, RNA & Protein SynthesisSynthesis

Chapters 12 & 13

The Structure of DNA

A little History

Year Scientist(s) Discovery

1928 Frederick Griffith Bacteria transfer genetic material from cell to cell.

1944 Oswald Avery, Colin Macleod &

Griffith had discovered DNA!Colin Macleod & Maclyn McCarty

1950 Erwin Chargaff Of the four possible nucloetides: As = Ts & Gs = Cs.

1952 Alfred Hershey & Martha Chase

Genetic material in viruses is also DNA.

1952 Rosalind Franklin Demonstrated that DNA is a helix.

1953 James Watson & Francis Crick

DNA is a double helix.

2000 Craig Venter & Francis Collins

Sequenced human DNA.

DNA

• In prokaryotes (no nucleus), DNA is circular.

• In eukaryotes, DNA is on the chromosomes in the nucleus.nucleus.

Structure of DNA

• Double-stranded helix

• Linked nucleotides

Nucleotide Parts

1) Sugar - deoxyribose

2) Phosphate group (has element phosphorous)

3) Nitrogenous base3) Nitrogenous base

• Sugar and phosphate make the sides.

• Bases make the rungs.

Nucleotide Types

1) Adenine (A)

2) Thymine (T)

3) Cytosine ( C )3) Cytosine ( C )

4) Guanine (G)

• A bonds with T

• G bonds with C

• Called complementary base pairing

DNA Replication

DNA Replication

When does it happen?

• Before cell division (mitosis or meiosis)meiosis)

Where does it happen?

• In the nucleus

DNA Replication: Step 1

• Enzyme (DNA Polymerase) unwinds DNA

DNA Replication: Step 2

• Enzyme attaches free nucleotides to the original strands until both strands until both strands are copied.

DNA Replication: Step 3

• Replication occurs in many spots along the DNA until all parts are copied.parts are copied.

• Two identical strands are made.

• Now cell division can occur!

• http://www.stolaf.edu/people/giannini/flashanimat/molgenetic

Replication in Different Cells

In prokaryotes: Starts at a single point and

In eukaryotes: Begins at many places and point and

proceeds in two directions until the entire chromosome is copied.

places and proceeds in two directions until the entire chromosome is copied.

RNA

Genes

• Section of DNA with the instructions to make 1 protein.

• Found in the • Found in the nucleus.

Proteins

• Many amino acids linked together.

• Proteins are made in the cytoplasm.

Click here for animation -> XX

• Proteins are made in the cytoplasm by ribosomes, but the instructions for doing this (the DNA) can’t leave the nucleus.this (the DNA) can’t leave the nucleus.

How can this work???

RNA

• A single-stranded copy of DNA.

DNA vs. RNA

RNA• Chain of

nucleotides.

DNA• Chain of

nucleotides.nucleotides.

• Sugar is ribose.

• Single-stranded.

• Bases are A,U,G,C.

(U = uracil.)

nucleotides.

• Sugar is deoxyribose.

• Double-stranded.

• Bases are A,T,G,C.

Types of RNA

Messenger RNA (mRNA)

• Copies DNA in the nucleus.

Transfer RNA

(tRNA)

• Brings amino acid to the ribosome for

nucleus.the ribosome for protein assembly.

Ribosomal RNA (rRNA)

• Inside ribosome. Helps with translation.

To go from DNA to a Protein, there are two steps:

1) Transcription- mRNA makes copy of DNA

2) Translation- protein is made from mRNA

Transcription: mRNA copies DNA

Step 1: enzyme (RNA Polymerase) unwinds DNA

promoter: regions of DNA where the promoter: regions of DNA where the enzyme binds

Step 2: mRNA bases make a copy of DNA

http://www.stolaf.edu/people/giannini/flashanimat/molgenetics/transcription.swf

Transcription (Part 2)

Step 3: introns (bad bases) are removed, exons (good bases) are spliced together

mRNA = AUACGUACmRNA = AUACGUAC

now = AUCUAC

Step 4: cap and tail are added

Step 5: mRNA leaves the nucleus for the cytoplasm.

Link <- Click Here for Animation

Ribosomes & Protein SynthesisSynthesis

Codons• A section of three

mRNA bases in a row that codes for one amino acid.

Anticodons

• The corresponding tRNA that carries the amino acid.the amino acid.

Translation: the mRNA is translated into a protein

Animation<- Click Here for Animation -> XX

1.) Ribosome finds the start codon, AUG, on mRNA.

2.) The corresponding anticodon on the tRNA binds into place.

3.) The ribosome reads the next codon & its corresponding anticodon binds. anticodon binds.

4.) The ribosome bonds the two amino acids on the tRNA together. The tRNA lets go.

5.) This continues until a stop

codon is reached. Then the

last tRNA & ribosome fall off.

6.) The amino acid chain folds

into its proper structure.

The central dogma of molecular

biology= DNA-> RNA->

protein

gene expression: gene expression: process by which a gene produces its product, which carries out its function

Mutations

• Changes in the DNA sequence that changes the protein it codes for.

What are mutations?

• Two Types:

1.) Chromosomal Mutations

2.) Gene Mutations

• Result from changes in a whole chromosome.

Chromosomal Mutations

1.) gene deletions

2.) gene duplications

3.) gene inversions

4.) translocations

• Parts of a chromosome break and rejoin, with a gene missing.

Gene Deletion

Ex: Cris-du-chat Syndrome

• Most duplications have no phenotypic consequences.

Gene Duplication

• Part of a chromosome becomes oriented in the reverse of its usual direction.

Inversion

direction.

• Usually no phenotypic consequences.

• Part of a chromosome breaks off and attaches to a nonhomologous chromosome.

Translocation

chromosome.

• Can lead to nonviable zygotes.

• Occur at a single point in the DNA.

• Usually one nucleotide is substituted for another, changing an amino acid.

Ex: Sickle Cell Anemia

Point Mutations

• Type of point mutation where an extra nucleotide is inserted or deleted, shifting the reading of codons, resulting in

Frameshift Mutations

the reading of codons, resulting in changes to ALL of the amino acids.

Ex: Huntingdon’s Disease

• An agent that causes a change in DNA.

Ex: smoke, high energy radiation (X rays, UV light, nuclear radiation), chemicals

Mutagen

UV light, nuclear radiation), chemicals (dioxins, asbestos, benzene, cyanide, formaldehyde), and high temperatures.

Note: In some cases, a gene mutation may have positive effects leading to evolution.

Gene Regulation & Expression Expression

How do cells regulate gene expression?

• Proteins bind to sections of DNA that control transcription.control transcription.

• More complex in eukaryotes because cells are specialized.

Differentiation• When new cells become specialized in

structure & function during embryonic development.

– In humans cells, this occurs 4 days after fertilization.fertilization.

Hox genes: a group of genes, located side by side on the same chromosome, that tell the cells how to differentiate as the body grows.

– Hox genes exist in the DNA of many animals-> evidence of common ancestors.