From DNA to Proteins

Lesson 1

Lesson Objectives

• State the central dogma of molecular biology.

• Describe the structure of RNA, and identify the three main types of RNA.

• Give an overview of transcription.

• Describe the genetic code.

• Explain how translation occurs.

Central Dogma of Biology• DNA is found in chromosomes.

– eukaryotic cells, chromosomes always remain in the nucleus

– proteins are made at ribosomes in the cell

• How do the instructions in DNA get to the site of protein synthesis outside the nucleus? – Another type of nucleic acid is responsible.– RNA, or ribonucleic acid – RNA is a small molecule that can squeeze

through pores in the nuclear membrane

• RNA carries the information from DNA in the nucleus to a ribosome in the cell and then helps assemble the protein

• Central dogma of molecular biology– DNA → RNA → Protein– the phase itself was coined by Francis Crick

RNA and Protein Synthesis

Genes are coded DNA instructions that control the production of proteins within the cell.

RNA molecules then carry out processes of making proteins.

Structure of RNA• Backbone => 5-C sugar and phosphate

group– DNA deoxyribose– RNA ribose

• Single- stranded– DNA double-stranded

• 4 Nitrogenous bases– Adenine– Uracil– Cytosine– Guanine

Types of RNA• 3 main types of RNA

– messenger RNA (mRNA)• Carry copies of instructions for assembling amino

acids into proteins

– ribosomal RNA (rRNA)• Proteins are assembled on ribosomes

– transfer RNA (tRNA) • Transfers each amino acid to the ribosomes as

specified by the coded message of mRNA

• Recall replication makes a

complementary copy of the

entire DNA molecules before

cells reproduce or divide

• RNA molecules are complementary copies of part of a nucleotide sequence in DNA that are made through the process of transcription– RNA polymerase

catalyzes

transcription

Transcription

• RNA polymerase binds

to DNA at very specific

sites known as promoters– promoters have specific

base sequences to start

and stop transcription

RNA Editing• Compiles the final mRNA molecule after

many eukaryotic genes are transcribed– Introns pieces that are removed

• Removed while RNA molecule still in nucleus

– Exons remaining portions • Spliced back together to form final mRNA

The Genetic Code

• Proteins made by joining amino acids into long chains called polypeptides.

Reading the Genetic Code• ‘Language’ of mRNA is the GENETIC

CODE– RNA 4 different nitrogenous bases:

• A, U, C, G

• Genetic Code is read 3 letters at a time– Each ‘word’ is 3 bases long

• Each 3 letter ‘word’ in mRNA is known as a codon

Examples of Genetic code

• RNA sequence– UCGCACGGU

• Read 3 bases at a time– UCG- CAG- GGU

UCG = Serine

GGU = Glycine

CAG = Glutamine

Translation• Ribosomes read mRNA and put together

polypeptides decoding= translation

Recap of Transcription/ Translation

The Roles of RNA and DNA

• DNA “ master plan”– Remains in nucleus

• RNA “blueprints”– Goes to protein-building sites in cytoplasm

• ribosomes

Genes and Proteins• Most genes contain only instructions for

assembling proteins– Genes that code for enzymes can produce

pigments for eye color, etc.– Other enzyme-coding genes produce your red

blood cell surface antigen thus determining your blood type

– Genes can also regulate rate of growth

• Many proteins are enzymes, which catalyze and regulate chemical reactions – Proteins are the key to almost everything

living cells can do