Protein Synthesis

DNA makes RNA, and RNA makes proteins.

Why does DNA make RNA?

DNA is a double

strand - too big to

leave the nucleus.

RNA is a single

strand – can leave

the nucleus.

12.3 DNA, RNA, and Protein

Molecular GeneticsChapter 12

Structure of RNA

Made up of subunits called nucleotides.

3 parts of RNA nucleotides:

a. Sugar - ribose

b. Phosphate group

c. RNA bases include

Adenine Uracil Cytosine Guanine

Molecular GeneticsChapter 12

3 Types of RNA

a. Messenger RNA (mRNA)- carries

instructions for amino acids from DNA

c. Ribosomal RNA (rRNA)- assembles

proteins on ribosomes

b. Transfer RNA (tRNA)- transfers amino

acids to make proteins

Molecular GeneticsChapter 12

Transcription: DNA makes RNA

DNA strand is unzipped and used to make

an RNA strand by adding RNA bases to

the opened DNA strand.

Molecular GeneticsChapter 12

DNA RNA

A - U (no T in RNA)

C - G

T - A

G - C

The RNA strand then leaves the nucleus and

enters the cytoplasm to make amino acids

during translation.

Molecular GeneticsChapter 12

RNA Processing

Non-coding sections called

introns are spliced out of the

RNA strand.

The coding sequences that

are left are called exons.

These will remain in the

mRNA strand to be

translated.

Translation:

RNA makes AMINO ACIDS which form proteins

RNA amino acids proteins

The RNA strand has

coded sections (exons)

that are “read” 3 letters at

a time to make an amino

acid.

Molecular GeneticsChapter 12

Chapter 12 Molecular Genetics

Each 3 letter “word” is a codon. Each codon

makes an amino acid. There are 64 different

codons that make 20 different amino acids.

methionine asparagine

Amino acids are joined until a stop codon (UAA,

UGA, UAG) – then the protein is complete.

Where does this happen? RIBOSOMES

mRNA strand

Protein molecule

Molecular GeneticsChapter 12

Amino acids

Molecular Genetics

What Do Proteins Do?

Transport materials into and out of the cell

Fight off viruses and bacteria

Form muscles, tissues, bones, and fluids

Make enzymes that speed up chemical reactions

Make hormones that send chemical messages

between cells

Chapter 12

Molecular GeneticsChapter 12

Molecular GeneticsChapter 12

Molecular Genetics

Causes of Mutations

Spontaneous

Chemicals and radiation

Radiation including X rays and gamma rays

12.4 Gene Regulation and Mutation

Chapter 12

UV sunlight – natural and artificial