Unit 7

• RNA, Protein Synthesis & Gene Expression

Chapter 10-2, 10-3 (page 190 – 197)

Chapter 11 (pg 203 – 214)

Unit 7

Lecture 1

Topics: DNA vs RNA

Covers: Chapter 10-2 Pages 190 - 191

RNA Introduction RNA (Ribonucleic Acid) is another type of

nucleic acid. Nucleic Acid – Organic compound, polymer

made up of monomers known as nucleotides

RNA uses the genetic information stored in DNA to create proteins. Remember:

DNA stores genes and is kept in the nucleus Gene – code for a protein

Ribosomes (outside nucleus) make proteins

Protein synthesis – process where a cell makes a protein

Protein Review Proteins are polymers made up of monomers known as amino acids 

A chain of many amino acids is known as a polypeptide Once a polypeptide is folded/coiled into its final shape, then it

is called a protein The shape (and function) of each protein is very different

A gene codes for the order of amino acids in a protein The sequence of amino acids determines how the polypeptide

will eventually coil/fold on itself (determines final shape of protein)

There are twenty different kinds of amino acids Each amino acid is coded for by a specific combination of nucleotides

Protein Review

Comparison of DNA and RNA

Nucleotide Components Function Structure VarietiesSugar Nitrogen

BaseDNA Deoxyribose Adenine

GuanineCytosineThymine

Stores genetic information

(genes)

Double helix (two strands connected in

center of helix)

Only one type

RNA Ribose AdenineGuanineCytosineUracil (a

pyrimidine)

Uses genetic information

to make proteins

Single helix (single strand

of nucleotides)

Three types- rRNA- mRNA- tRNA

Remember: a gene is a code for a protein

Comparison of Three types of RNA

rRNA (Ribosomal RNA) Makes up part of a ribosome

Remember: Ribosomes are made up of RNA and proteins Ribosomes are organelles that make proteins

Comparison of Three types of RNA

mRNA (Messenger RNA) Brings the genetic message from

DNA to a ribosome DNA gene (protein message)

copied into mRNA

Comparison of Three types of RNA

tRNA (Transfer RNA) Used during protein synthesis Transfers amino acids to their proper

place in the amino acid chain  

END OF LECTURE 1

Unit 7

Lecture 2

Topic: Introduction to

Protein Synthesis

Covers: Chapter 10-2 and 10-3 Pages 191 – 195

Protein Synthesis

DNA (Chromosomes) store genetic information. Each strand of DNA stores hundreds of genes

The order (sequence) of nucleotides in the gene codes for the order of amino acids in the protein A mutation that occurs in a gene could affect the protein code

Mutation – change in the order of nucleotides (DNA or RNA) A gene mutation could change the order of amino acids in

the protein or could prevent the protein from being made

Protein Synthesis

To make a protein:1. A copy of a gene is made (DNA copied into mRNA)

This mRNA template serves as the code for the protein, instructions for how to make the protein

2. mRNA carries the protein code from the nucleus to a ribosome Protein synthesis takes place outside the nucleus by a:

Bound ribosome – makes proteins to leave the cell Free ribosome – makes proteins to be used in the cell

3. Ribosome translates mRNA sequence into an amino acid sequence4. The chain of amino acids will fold into final protein product

Protein SynthesisThe Genetic Code

The order of nucleotides in the mRNA template codes for the order of amino acids in the protein chain

Ribosome translates the information from mRNA into amino acids mRNA is made up of nucleotides; Proteins made up of amino acids

Protein SynthesisThe Genetic Code

A combination of three nucleotides codes for one amino acid CODON – Three nucleotide sequence that

codes for an amino acid 64 codons, but there are only 20

amino acids Some amino acids have more than one

codons Important codons: START (AUG), and

STOP (UAA, UAG, UGA)

• Phenylalanine (Phe), Leucine (Leu), Isoleucine (Ile), Methionine (Met), Valine (Val), Serine (Ser), Proline (Pro), Threonine (Thr), Alanine (Ala), Tyrosine (Tyr), Histidine (His), Glutamine (Gln), Asparagine (Asn), Lysine (Lys), Aspartic acid (Asp), Glutamic acid (Glu), Cysteine (Cys), Tryptophan (Trp), Arginine (Arg), Glycine (Gly)

Protein SynthesisThe Genetic Code

Each amino acid is carried through the cell and to the ribosome by a specific tRNA (Transfer RNA)

tRNA is shaped like a “t” One end (end of chain) bonds to a specific amino acid Opposite end (bottom loop end) attaches to mRNA

This section is known as the ANTICODON Anticodon is complementary to each mRNA codon Example: Amino Acid – Serine

CODON – “AGU” Serine transferred to amino acid chain by tRNA

with the ANTICODON – UCA

End of Lecture 2

Unit 7

Lecture 3

Topic: Protein Synthesis Transcription Translation

Covers: Chapter 10-3 Pages 193 – 196

Protein Synthesis

• Protein Synthesis is a two part process

1. Transcription• This is when a gene is transcribed (copied) • DNA gene copied into mRNA

2. Translation• This is when the genetic code is translated

into a protein• mRNA message translated into amino acids• Amino acid chain shaped into final protein product

Transcription

1. RNA Polymerase (an enzyme) binds to a gene on the DNA RNA polymerase separates the two strands of DNA

Transcription

2. One of the separated DNA strands is copied This DNA strand is known as the TEMPLATE

3. RNA Polymerase moves along the DNA template and adds the complementary RNA nucleotide

DNA RNAComplementary Base

Guanine CytosineCytosine GuanineThymine AdenineAdenine URACIL

Transcription

4. RNA polymerase continues until it reaches the end of the gene

5. RNA Polymerase releases DNA and gene copy (mRNA template) DNA strands bond back together, goes back to double helix mRNA template will leave the nucleus and go to a ribosome

Transcription

Translation

• Once the mRNA reaches a ribosome, the genetic message will be translated into a protein• The ribosome will scan down the mRNA strand, translating

each codon into an amino acid• tRNA transfers each amino acid into the proper place based on

the mRNA message• Remember:• A CODON (in mRNA) codes for one amino acid• Each amino acid is transferred in place by tRNA• ANTICODON – in tRNA, complementary to codon

• PROTEIN – polymer made up of monomers of amino acids

Translation

Translation

1. mRNA leaves nucleus and goes to a ribosome to begin protein synthesis

2. Ribosome will attach to the end of the mRNA. The ribosome will begin to move down the mRNA template. tRNA will also begin to transport amino acids (floating in cytosol)

to ribosome Each amino acid is carried by a different tRNA

Translation

3. The ribosome will "scan" down the mRNA template until the ribosome reaches the start codon of mRNA.  

When the ribosome reaches the start codon (AUG), the ribosome will stop moving.

tRNA with the anticodon (UAC) can bond with the start codon. tRNA adds first amino acid of the chain: methionine (MET)

Translation

4. After the first amino acid is attached, the ribosome will move down to the next codon. The next codon will be translated.

tRNA will attach the amino acid MET and the second amino acid will bond together

Peptide bonds hold the amino acids together Peptide Bond – covalent bond between amino acids

5. Ribosome will continue to move down the mRNA strand, stopping at each codon.

tRNA attaches to each codon and adds the correct amino acid. The amino acids are attached in a chain by peptide bonds.

Translation

6. When the ribosome reaches the “STOP” codon, no more amino acids are added

"STOP" codons (UAA, UAG, UGA) don’t code for an amino acid

7. Long chain of amino acids is released Long chain of amino acids – Polypeptide

8. Ribosome separates from the mRNA strand.

9. Polypeptide will coil/fold into its final shape, it will then be known as a protein

End of Lecture 3

Unit 7

Lecture 4

Topic: Cell Differentiation Gene Expression

Covers: Chapter 11 Page 209

Cell Differentiation

Only certain sections of the DNA molecule code for a gene A gene is a section of DNA that codes for a protein The longer the strand of DNA, the more genes it can store Non-coding Region – Sections of DNA that do not code for

proteins

Cell Differentiation

In a multicellular organism, every cell in the body has the same DNA Every cell in the body came from one cell – a fertilized egg

(embryo) Embryo divides numerous times to add new body cells

Uses process of mitosis to add new body cells (Somatic Cells) This means that every cell in our body has the same genes In humans, each somatic cell is a diploid cell and has 46

chromosomes

Cell Differentiation

Every cell in a multicellular organism contains all of the organism’s genes But, each cell does not need to use every gene to function

properly.

Differentiated (specialized) cells only use the genes necessary for that cell type to function Only makes the necessary proteins for that cell type

Cells can regulate which proteins they make by controlling which genes are activated and used to make proteins.

Gene Expression

GENE EXPRESSION - activation of a gene that results in the formation of a protein. A gene is expressed when it is copied into RNA

Control of gene expression is very important in embryo development and as cells are becoming specialized Before cells become specialized, they are known as Stem Cells Stem cells activate certain genes & begin to become specialized

This causes the cell to change its shape to take on its final specialized form and function

Remember: Our body is made up of over 200 different types of cells! Each cell/tissue type has its own unique form & function

End of Lecture 4