Nucleic Acids and Protein Synthesis

Modern Biology – Chapter 10

• I. Molecular Biology Processes

• A. Replication -- copying of DNA

• 1. Occurs in nucleus

2. Identical DNA strand is made

• B. Transcription -- DNA to mRNA

1. (mRNA) copied to move outside

nucleus

C. Translation -- of message into protein

sequence

1. Occurs in the cytoplasm at the

ribosome

2. Amino acids are assembled to

a. Proteins - physical structure

b. enzymes - catalyze other molecules in body

Scientists involved with discovering the double helix

Many scientists figured out a piece to the puzzle

1. Most notable: Watson and Crick

2. Also: Rosalind Franklin and Maurice Wilkins

DNA – Deoxyribonucleic Acid

A. Organic molecule that carries the blueprints of living organisms

1. Stores and transmits the genetic information2. Controls the production of protein

B. Composed of repeating subunits - nucleotides

Nucleotides

A. Each nucleotide has three parts1. A five – carbon sugar called deoxyribose

2. A phosphate group (phosphorous

surrounded by oxygen)

3. A nitrogen base (4 kinds)a. adenine, guanine, thymine, cytosine

Nitrogen Bases

4. Purinesa. Adenine and guanine

b. Contain a double ring of carbon and nitrogen

5. Pyrimidinesa. Thymine and cytosine

b. Contain a single ring of carbon and nitrogen

DNA Structure

DNA Structure

• DNA is a double helix – like a spiral staircase

• Complementary Base Pairing - A weak hydrogen bond holds nitrogen bases together:• Adenine bonds with thymine to form a step

• Cytosine bonds with guanine to form a step

• Deoxyribose sugar and phosphate are backbone or sides of the ladder – covalently bonded together

DNA Replication

• Cells that divide must pass exact copies of their DNA to offspring cells

• Complementary base pairing allows for complementary nucleotide chains

• This led to the discovery of how DNA copies itself

• The two nucleotide chains must unwind and each chain serves as a template for a new chain

DNA Replication

• First Step – the separation of the two nucleotide chains

• They separate at a point called the replication fork

• The chains are separated by helicase enzymes, which break the hydrogen bonds between the nitrogen bases

Replication of DNA

• Next Step – the addition of nucleotides to each side of the unwound DNA molecule

• DNA polymerase enzymes add nucleotides by covalently bonding a sugar to a phosphate

• Each strand reacts with complimentary bases floating in the nucleus

• The bases are joined through hydrogen bonding

• Copying occurs at many points on DNA

Accuracy and Repair of DNA

A. DNA replication is accurate - usually only 1 error in every 10,000 paired nucleotides

B. But any error, called a mutation, can have serious effects

C. Radiation, chemicals , heat can damage DNA (mutation)

D. Cell has proofreading techniques – like spell check

E. Over 20 or more repair enzymes fix errors

Do Now

• What is the function of DNA?

• What are the 4 nitrogen bases in DNA nucleotides and how do they pair up?

• What are the two main enzymes involved in DNA replication?

RNA• The DNA that contains the genetic code to

make all of your proteins is trapped in the nucleus

• The ribosomes, enzymes, and amino acid building blocks of protein are out in the cytoplasm

• RNA is responsible for getting the code from the nucleus to the cytoplasm

• Copies DNA and then moves outside the nucleus to synthesize proteins

RNA – Ribonucleic AcidLike DNA it is made up of repeating

nucleotides

Differences between DNA and RNA:

RNA single stranded

RNA has ribose sugar rather than deoxyribose

RNA uses Uracil nitrogen base rather than Thymine to pair with Adenine

Types of RNA

A. Messenger RNA

B. Transfer RNA

C. Ribosomal RNA

Messenger RNA (mRNA)

• Single uncoiled chain of RNA that transmits DNA’s information from nucleus to cytoplasm

Transfer RNA (tRNA)

• 80 RNA nucleotides folded into a hairpin shape

• There are ~ 45

different ones

that bind to

specific amino acids

Ribosomal RNA (rRNA)

• Consists of RNA nucleotides in globular form – most abundant RNA type

• Along with proteins,

rRNA makes up the

ribosomes where

proteins are made

Transcription

• Process by which genetic information is copied from DNA to mRNA

• An enzyme – RNA polymerase – initiates transcription by binding to promoter regions on DNA

• As RNA polymerase binds to promoter, the DNA molecule separates

• Only one of the DNA strands acts as a template

TranscriptionRNA polymerase connects

RNA bases to the growing RNA strand

The same as when DNA is replicated but uracil is used instead of thymine

It continues until it reaches a termination signal

Do Now

• How is RNA different from DNA?

• What are the three types of RNA?

• What is the purpose of Transcription?

Translation - Protein Synthesis

• Proteins are polymers of amino acids

• There are 20 different amino acids

• The sequence of amino acids determines the structure of the protein

• The function of the protein depends on its structure

Translation - Protein SynthesisA. The sequence of nucleotides in an mRNA

strand is translated into a sequence of amino acids to make a protein

B. A series of three nucleotides on RNA, or codon, codes for one amino acid.

C. There are 64 codons and only 20 amino acids, so several codons can code for the same amino acid

D. There are also a start codon (AUG) and stop codons (UAA, UAG, UGA)

Translation - Protein Synthesis

• mRNA carrying the genetic code from DNA enters the cytoplasm and meets up with a ribosome

• Ribosomes bind to mRNA and tRNA

• Amino acids floating in the cytoplasm are brought to the ribosome by tRNA

Translation - Protein Synthesis

• Each tRNA molecule has a region that bonds to a specific amino acid

• Each tRNA also has a sequence of three nucleotides called the anticodon

• The anticodon is complementary to and pairs up with a corresponding mRNA codon.

Translation

A. mRNA moves out of the nucleusB. mRNA goes to ribosomes and attaches to start codon

(AUG)C. tRNA moves amino acids in cytosplam to ribosomeD. tRNA anticodon bases pair with codon and drag

amino acid to add to polypeptideE. Ribosome enzymes create peptide bonds between

amino acidsF. Amino acids are added until stop codon is reached