Making Proteins!!!Objectives:

1. Explain the structure of RNA2. Explain how proteins are made in the cell.3. Explain the function of mRNA, rRNA and

tRNA

1. In your investigation yesterday, you mixed banana with dish detergent. What was the purpose of this?

2. In this experiment how did I break apart the cell wall?

3. Why is DNA considered to be the source of diversity among all living things?

4. Copy this DNA sequence and write its complementary sequence. GAA TTA ACA

5. What is the purpose of DNA replication?

Quiz

all the codes located on the DNA of the 23 pairs of chromosomes are referred to as the genetic code

the genetic code consists of the lengthwise sequence of nitrogen bases found along a DNA molecule e.g. ATTGCAGGCCTAATT

the genetic code is written in triplets of nitrogen bases (three letter words or codons) e.g. ATT GCA GGC CTA ATT

each triplet represents one amino acid in the final protein

The DNA Code – Genetic Code

RNA is a type of nucleic acid It is a three part molecule including a

phosphate, sugar and nitrogen-containing base component.

The sugar is ribose and the nitrogen-containing base is one of the following four: adenine, cytosine, guanine or uracil

It is single stranded It is a helper to DNA allowing protein

synthesis to occur.

RNA

in the genetic code, more than one codon can be used to code for a particular amino acid; e.g. serine is coded for by UCU, UCC, UCA, or UCG

there are three “STOP” codons, which do not code for any amino acids, but which indicate the end of the protein chain

the genetic code for amino acids is universal in all living organisms◦ a gene from one species may be inserted into

another species, and be fully functional e.g. bacteria, using a human gene to produce insulin – a protein

Protein synthesis (building of a protein in the cell) is a 2 step process:

1) Transcription (copying DNA in the nucleus)

2) Translation (building a protein in the cytoplasm)

Overview of Gene Expression – Protein Synthesis

Transcription occurs in the nucleus it involves DNA and mRNA one DNA gene is “transcribed”

(copied) to form a complementary copy referred to as messenger RNA (mRNA)

1) Transcription

DNA unwinds or unzips at a specific gene site

remember, a gene is a short segment of DNA coding for a single protein

one side of the DNA gene, the template strand, will be copied

free RNA nucleotides in the nucleus form complementary base pairs with the template DNA strand

STEPS:

the new mRNA molecule formed is a single linear strand

mRNA then leaves the nucleus and enters the cytoplasm

mRNA attaches itself to a ribosome

STEPS (cont’d)

NOTE: a sequence of 3 nitrogen bases on mRNA is

referred to as a codon. these codons are complementary to the

triplets of the original DNA gene thus, a mRNA molecule is a complementary

copy of a gene on the DNA molecule and carries the genetic information on how to build a particular protein

 

Translation occurs in the cytoplasm it involves mRNA, the ribosome, tRNA

and amino acids the codons on mRNA are “read” and

“translated” by the ribosome into a sequence of amino acids that will form a protein molecule

2) Translation

mRNA arrives from the nucleus and attaches itself to a ribosome

the first mRNA codon is in the first slot on the ribosome awaiting tRNA

a tRNA molecule in the cytoplasm picks up an amino acid that corresponds to its anti-codon

the tRNA and its attached amino acid then travels to the ribosome and the anticodon on tRNA bonds with the codon on mRNA following the complementary base pairing rule. This ensures that the correct amino acid is in place

STEPS:

the second mRNA codon is available in the second slot on the ribosome (A site)

a second tRNA with its attached amino acid arrives and its anticodon bonds to the mRNA codon

now the two amino acids are bonded together forming a peptide bond, with the help of an enzyme

the first tRNA leaves, and the ribosome shifts down the mRNA, exposing the third codon

STEPS (cont’d)

this process continues until all the amino acids have been bonded together into a long chain

when the ribosome reaches a stop codon, no more amino acids are added and the building of a polypeptide, which is a small portion of what will become the large protein molecule, is complete

the protein is released and folds up into its final functional form

STEPS (cont’d)

http://www.youtube.com/watch?v=NJxobgkPEAo

http://www.youtube.com/watch?v=983lhh20rGY&feature=related

Diagram

Questions1. Compare DNA and RNA. What is the function of

each? Where is each located in a cell?

2. Why is genetic material crucial to the well-being of a cell

3. State the function of rRNA, mRNA and tRNA

4. Draw a diagram illustrating the process of protein synthesis. Make sure to label your diagram.