Gene

a unit of hereditary information which can be passed on to future generations

Amino Acids

• building blocks of proteins (polypeptides)
• there are 20 amino acids

Codon

• a nucleotide triplet code
• codes for a specific amino acid

DNA

• found only in nucleus
• made up of deoxyribose sugar
• contains 2 strands
• contains A, T, C, G
• can be copied or replicated
• there is only one form of DNA

RNA

• found in the nucleus and the cytoplasm
• composed of ribose sugar
• single stranded
• contains A, U, C, G
• cannot be copied or replicated
• comes in 3 forms (mRNA, tRNA, rRNA)

Transcription

mRNA strand is build from the code on the DNA strand (gene)

Translation

mRNA strand is used at the ribosome to help join amino acids to form a protein

mRNA

(messenger RNA)

carries an RNA "copy" of the DNA gene code from the nucleus to the cytoplasm

tRNA

(transfer RNA)

transports amino acids from the cytoplasm to the ribosome so they can be joined to make a protein

rRNA

(ribosomal RNA)

molecules of rRNA make up the ribosomes 2 units along with proteins

Requirements for

Transcription

1. a gene segment on the DNA
2. many RNA nucleotides that are floating freely in the cytoplasm
3. the enzyme RNA polymerase

Steps in Transcription

1. DNA unwinds at the area where the gene is located
2. The hydrogen bonds between the two strands of DNA break
3. Free floating RNA nucleotides bond w/ the complimentary DNA strand
4. the completely formed mRNA breaks away from the DNA
5. DNA forms reconnect and mRNA is free to go to cytoplasm

Start Codon

AUG codes for the amino acid methionine. 

It signals the ribosome that it is the beginning of the mRNA sequence.

Stop Codon

UAA, UAG, UGA

Do NOT code for an amino acid

Signal the ribosome that it is the end of the mRNA sequence and triggers the release of the mRNA from the ribosome

Requirements for

Translation

1. mRNA carries the DNA code as "codons"
2. ribosome (site of protein synthesis)
3. tRNA that carries the amino acids from the cytoplasm to the ribosome to be joined to form a protein

Steps in Translation

(part 1)

1. mRNA joins with the ribosome
2. tRNA (w/ amino acid attached) joins the mRNA codon to the ANTI-codon
3. a second tRNA with an attached amino acid joins the mRNA
4. peptide bond forms between the first 2 aminio acids

Steps in Translation

(part 2)

5.  the first tRNA is released from the mRNA

6.  the mRNA slides through the ribosome to expose the next codon

7.  the next tRNA w/ a.a. joins the mRNA

8.  repeat steps 4-8 until a stop codon is reached

mRNA and protein is released from the ribosome.

How do proteins differ?

• number of amino acids
• types of amino acids
• sequences of amino acids

Gene Mutations

any change in the normal sequence of nucleotides in a gene sequence.

Mutagens

(examples)

• UV light
• chemicals like those found in cigarette smoke
• viruses like HPV (human papilloma virus)
• X-rays, gamma rays

Types of Mutations

1. Addition
2. Deletion
3. Substitution

"Addition" Mutation

the addition of an extra nucleotide

within a gene sequence

"Deletion" Mutation

deletion of a nucleotide within

a gene sequence

"Substitution"

Mutation

substitution of a different nucleotide for

one normally present in a

gene sequence

Protein

Polypeptide

smaller, non-functional group of amino acids; can be combined with others to make a protein so it is "part of a protein"

Trait

any physical, physiological or behavioral trait

Ribosome

Site of protein synthesis

Uracil

nitrogen base that replaces thymine in RNA

RNA polymerase

enzyme used during transcription

Anticodon

three nucleotide triplet code carried by the tRNA; complementary to the codon on the mRNA

Cellular Specialization

cells 'turn on' or transcribe and translate only those genes that code for the proteins they need.  Other genes are 'turned off' because the proteins they code for are not needed by the cell

Coding DNA

Nucleotide sequences that code for proteins or polypeptides

(3% of human genome)

Non-coding DNA

Nucleotide segments that do not code for proteins or polypeptides.

(97% of human genome)