From DNA to ProteinsFrom DNA to ProteinsChapter 13

Review the answers to the following questions to test your understanding of previous material.

1. DNA performs two unique functions necessary for the perpetuation of life. Briefly describe these two functions.

2. Discuss the significance of specific base pairing in DNA replication (and RNA synthesis).

3. Describe the concept of a gene: where are they, what do they do, and how are they inherited?

4. What are mutations: what causes them, are there different kinds, and can they be repaired?

5. What is the relationship between the informational molecules DNA and RNA?... between these molecules and proteins?

6. List and describe several roles of different proteins in cells. (In other words, why is protein synthesis important?)

Before you go on…

Learning Objectives

1. Compare and contrast the chemical structure and function of DNA and RNA.

2. Discuss the significance of specific base pairing in DNA replication and in RNA synthesis.

3. Name the enzymes important in DNA and RNA synthesis.4. Differentiate between the processes of transcription and

translation.5. Describe the roles of the 3 different types of RNA in

protein synthesis.6. Messenger RNA contains a start codon and a stop codon.

Why is this necessary?7. Describe what is happening during cell differentiation and

animal metamorphosis.8. Describe the inherited component of cancer development?

What happens?

Three Classes of RNAs• Messenger RNA (mRNA)

– Carries protein-building instructions

• Ribosomal RNA (rRNA)

– Major component of ribosomes

• Transfer RNA (tRNA)

– Delivers amino acids to enzymes at ribosomes, in

the order dictated by mRNA, to build correct

polypeptide

Where is RNA made? What two kinds of molecules make up a ribosome? Where do you find ribosomes in a cell?

p. 196

Transcription & DNA Replication

•Nucleotides added as in DNA replication (specific base pairing)

•Unlike DNA replication,only small stretch acts as a template

•RNA polymerase catalyzes nucleotide addition

•Product is a single strand of RNA

When is DNA replicated normally?

Name the enzyme that catalyzes the replication of DNA.

p. 196

Same two steps produce all proteins:1) Transcription:

• DNA is transcribed to form mRNA• occurs in the nucleus• mRNA moves into cytoplasm

2) Translation: • translation occurs at ribosomes

(rRNA)• mRNA is translated by tRNA to form

polypeptide chains, which fold to form functional proteins

Steps from DNA to Proteins

Hopefully, nothing is lost in translation!

DNA to

ProteinWhere might this ribosome be in the cell?

What has yet to happen to this polypeptide chain (before it is a functional protein)?

Where might this protein be used in the cell?

DNA & RNA compared…

DNA:• Double stranded• Self replicating• ACTG bases

RNA:• Single stranded• Manufactured from

DNA• ACUG bases

Match base pairs in DNA replication:

Match base pairs for RNA synthesis:A -

G -

C -

T -

A -

G -

C -

T -DNA template

T

C

G

A

U

C

G

A

p. 196

The “language” of Nucleic Acids

• mRNA (messenger RNA): a “copy” of DNA that is read in codons.

AUG GCA UUU GCA …

U A C

Amino Acid

• tRNA (transfer RNA): ‘interpreter’ of mRNA using “matching” anticodons.

AUG GCA UUU GCA …

How many triplets are in a gene that codes for a polypeptide that’s 125 amino acids long?

• DNA codes for amino acids in triplets: TAC CGT AAA CGT …

If the recipe for proteins only had 4 words (ACTG), how would this limit the variety of proteins possible?

p. 198

p. 198

Protein synthesis

DNA

A

T

G

G

G

A

mRNA

U

A

C

C

C

U

tRNA

A

U

G

Tyr

ProG

G

A

transcriptiontranslation

Review mutations… what are the possible effects to the individual? Can these mutations be passed on to offspring?

p. 200

Mutations in Genes p. 202

What Happens to the New Polypeptides?

• Where is the ribosome?

• Some function in the cytoplasm

• Many enter the endoplasmic reticulum and move through the endomembrane system where they are modified and shipped to their final destination

Animal Metamorphosis

What has changed inside cells to produce these changes in body form. How is this controlled? What is/are the advantages of metamorphosis?

Cancer• Tumors result when the normal mechanisms

controlling cell division malfunction.• Benign or malignant• Result from the accumulation of mutations

that transform the cell• Mutagens and carcinogens increase the risk

of cancer– Tumor suppressing genes– Proto-oncogenes

• Viruses can insert genetic information into host cells, and move genes to different chromosomes– Can we take advantage of this?

p. 204