DNA determines your unique characteristics. A Review…

• DNA is the instructions for making proteins.• DNA determines the structure and function of the

protein molecules that carry out:– your cell functions– your cell structures.

• YOU ARE YOUR PROTEINS! –Physical traits that you have that are different

from those around you are different because the structure of your proteins is different.

• Transcription is the beginning of how proteins are built from DNA insturctions.

Review the worksheet & add a few detailsThe 1st part of going from DNA to protein: an mRNA

copy of DNA is made through TRANSCRIPTION in the nucleus. *This is done because DNA can not leave the nucleus.

A. Steps:1. The enzyme RNA POLYMERASE separates the

2 strands of DNA.2. RNA polymerase then uses ONE strand of

DNA as template and adds complementary base pairs (Uracil instead of thymine)

3. When the end of the gene is reached, mRNA breaks off the DNA and leaves the nucleus.

4. DNA twists back up by reconnecting their hydrogen bonds.

mRNA? What’s that?

There are 3 different types of RNA:• fold differently =• different functions

1. MESSENGER (mRNA): is a complementary copy of DNA that leaves the nucleus to direct the making of proteins.

2. TRANSFER (tRNA): specialized RNA molecule that carries amino acids which are used to make proteins.

3. RIBOSOMAL (rRNA): makes up parts of the ribosomes which are the sites of protein synthesis.

The following diagram shows the strands of DNA unwinding and RNA nucleotides being added…

This diagram just shows how the RNA strand breaks off

from the DNA template…

• http://www.hhmi.org/biointeractive/dna/DNAi_transcription_vo2.html

• Once we have the mRNA the information must be “translated” from the “language” of nucleic acids to proteins.

• As a table, pair (a person from your table), or individual you will read through the translation worksheet and answer the questions.

• What you do not finish will be HW due next class.• Think through the questions

Reminder!

A. proteins are macromolecules: monomer is AMINO ACIDS.

1. 20 amino acids naturally occurring in living organisms.

2. The 20 amino acids can be joined together in any order and # so the possible number of different protein structures in virtually limitless.

3. Think Alphabet (26) make all the words ever

4. The function of a protein is determined by the order of amino acids which are determined by DNA.a. If you change the order/# of amino acids

in the protein then its structure is changed.

b. If its structure is changed then so is its function.

B. DNA to protein: first the sequence of DNA nucleotides of one gene is transcribed into a sequence of mRNA.1. mRNA is “read” as a series of CODONS

which is a set of 3 nucleotides.2. Each codon specifies a singleamino acid that will be placed to form a protein.

http://www.hhmi.org/biointeractive/dna/DNAi_triplet_code.html

So the process basically works like this….

Basic animation

• http://www.youtube.com/watch?v=1PSwhTGFMxs• http

://www.hhmi.org/biointeractive/dna/DNAi_translation_vo1.html

1. mRNA attaches to a RIBOSOME at start codon

Start Codon

2. As ribosome moves, anti-codon tRNA complimentary base pairs to codon.

3. amino acid dropped off. Amino Acids

tRNA

Anticodon

*This is how the DNA instructions are followed & appropriate placement of the amino acids is accomplished creating the correct protein.

4. The process continues until a stop codon is reached.

5. The protein is then released from the ribosome.

This diagram shows a step by step of the beginning of translation…

1

3. 4.

2.

To make the process of translation faster and to make many copies of a protein, multiple ribosomes can move along mRNA at

once looking something like this…

Summary (Know this stuff)

• Transcription converts DNA code to mRNA– Occurs in nucleus

• Translation converts mRNA code into a protein– With help of tRNA in ribosome

• The structure and shape of the protein depends on the DNA sequence

Keep in mind…• Genes don’t code for

traits• They code for proteins

(or parts of proteins) that can affect traits

• i.e. they can code for a protein that makes eyes blue

• Differences in DNA determine differences in proteins = differences in physical traits.

1 Gene 1 Protein

• A gene gets transcribed into messenger RNA

• Messenger RNA is translated into a protein

• HOMEWORK: It’s in the genes!• This worksheet will prepare you for the

next activity: modeling protein synthesis aka: transcription/translation