Chapter 10

Objectives Compare the structure of DNA and RNA Summarize the process of transcription Outline the major steps of translation

SCS:B-4.4

Traits are determined by proteins that are built according to the instructions found on DNA

Proteins are not built directly from DNA but from RNA (ribonucleic acid) Copy of the DNA that is decoded

Single stranded string of nucleotides Different bases

Has uracil instead of thymine Different sugar – ribose

A gene’s instructions for making a protein are coded in the sequence of nucleotides in the gene

Instructions are transferred from DNA to RNA in a process called transcription

The instructions are then decoded to make a protein in a process called translation

Takes place in the nucleus of eukaryotic organisms and in the cytoplasm of prokaryotic organisms

1. RNA polymerase binds to the DNA molecule at the specific sequence that needs to be translated

2. RNA polymerase unwinds and separates strands

3. RNA polymerase adds nucleotides and links complimentary base until it reaches a “stop” signal.

4. RNA detaches then it leaves the nucleus to be translated.

3 types of RNA are made during transcription Messenger RNA (mRNA) – copy of the DNA Transfer RNA (tRNA) – carries nucleotides

to the ribosome Ribosomal RNA (rRNA) – part of the

ribosome

RNA instructions are written as a series of 3 nucleotide sequences of mRNA called codons

Each codon codes for an amino acid or a start or stop signal

the sequence can be decoded using the a genetic code Specifies the amino acid, so it tells you

what protein is being made Nearly universal

Takes place in the cytoplasm mRNA, tRNA, and rRNA are involved Ribosomes are the site of protein

synthesis Translation can take place at multiple

places on the mRNA

1. mRNA leaves the nucleus; ribosome attaches at the start codon (AUG)

2. tRNA brings the complimentary anticodon with a amino acid attached

3. A peptide bond forms after another tRNA brings a second amino acid

4. The ribosome continues the above process until a stop message is reached in the mRNA.

5. The newly made protein detaches and the ribosome break apart.

Objectives Summarize how protein synthesis is

regulated Describe the types of mutations that

can occur during translation

SCS:B-4.4

Protein synthesis is controlled by “on” and “off” switches This switch is called an operator

Controls the access of RNA polymerase to the sequence of DNA

A protein (repressor) binds to the DNA to keep RNA polymerase from binding to the promoter site (the group of genes that codes for a specific protein)

Regulation is more complex in eukaryotic organisms Regulated in many ways

Most of your DNA does not code for anything useful Introns – non coding region

Are “cut” out during translation Exons – regions that actually code for

proteins

Types of point mutations (occur in only a few nucleotides) Substitution Insertion Deletion

Mutations can result in no protein being made, a nonfunctional protein, or have no affect at all

Many genetic disorders are a result of a single nucleotide mutation