Chapter 8DNA and GENES

Biology Notes

Information Storage in Cells

• Instructions for cell functions are stored in the nucleus within the chromosomes

• Chromosomes are made of DNA molecules

• DNA stands for:

DEOXYRIBONUCLEIC ACID

What is DNA?• Genetic information that determines an

organism’s traits.

• Controls by proteins: skin, muscles, bones, etc.

• Proteins = Enzymes

Watson & Crick

• DNA is made of two chains of nucleotides joined together by the nitrogen bases.

• Proposed DNA is shaped like a long zipper that is twisted.

• Double Helix has two twisted strands that form a spiral.

Structure of DNA

• Very long molecule made up of nucleotides

Each nucleotide consists of :

1) One deoxyribose sugar (simple sugar)

2) One phosphate group (phosphorus surrounded by 4 oxygen atoms)

3) One nitrogen base

Nitrogen Bases• Carbon ring structure w/ four

nitrogen atoms.

Will be one of four possible bases:

1. Cytosine = C

2. Guanine = G

3. Adenine = A

4. Thymine = T

Nitrogen Base Pairs

• Nitrogen Bases pair with a specific partner: (Complimentary Pairs)

• Adenine = Thymine (A – T)

• Guanine = Cytosine (G – C)

• Hydrogen bonds between the nitrogen bases bond them together

A Cytosine Nucleotide

P

S C

Today’s DNA molecule• Referred to as a double helix

Visually it is like a long twisted ladder:

1. Sides are made up of phosphate – sugar groups

2. The steps are made of pairs of nitrogen bases

Phosphate and sugar groups

C - G

G - CT - AT - A

G - CA - T

G - C

DNA Replication• When a cell reproduces in the nucleus

it must make copies of itself

• Each new cell must have same info as the parent cell

• Occurs during Interphase

DNA Replication Process:

1. An enzyme breaks the Hydrogen bonds between nitrogen bases (“Unzipping” the double helix)

2. Free floating nucleotides, surrounding the DNA molecule, are bonded to the exposed nitrogen bases. (Base Pairing)

3. Another enzyme bonds the nucleotides into a chain. (Creates the backbone to the new chain)

4. Process continues until there are 2 new DNA molecules that are identical to one another. (Final product, 2 from 1)

Process of Replication

1. A-T

A-T

T-A

G-C

G-C

T-A

A T

A T

T A

G C

G C

TA

2. A-T A-T

A-T A-T

T-A T-A

G-C G-C

G-C G-C

T-A T-ADNA Helix

Begin to split New bases come in

Final step of Replication2 identical DNA molecules

A-T A-T

A-T A-T

T-A T-A

G-C G-C

G-C G-C

T-A T-A

Protein Synthesis

Reading the DNA molecule to make proteins.

How DNA controls cell functions

• DNA instructs cell ribosomes to make proteins. It tells them what kind and how many to make.

• Some of the proteins are enzymes

How DNA controls cell functions

1. Enzymes control what a cell will do

2. Enzymes control the cells chemistry

• All proteins are made up of smaller units called Amino Acids. There are 20 different types of Amino Acids

• By combining amino acids in different sequences different proteins can be made

• DNA controls the sequence of amino acids in a protein

• Therefore it controls what kinds of proteins are made by the cell ribosomes

How DNA controls amino acid order in a protein

• Order of bases in 1 strand of DNA ( called master strand) determine order of amino acids in a protein.

• Order of bases in master strand is called the Genetic Code

• Code is read as a sequence of 3 bases called triplets

• Each triplet determines which amino acid is to be placed where in a protein

• Small segment of DNA master strand could have following genetic code

G----T----C----A----A----T----G----G----C1. There are 3 triplets in this code2. GTC, AAT, GGC3. GTC is the triplet code for amino acid

glutamine AAT is triplet code for amino acid

Leucine GGC is triplet code for amino acid

Proline

• Protein being made form genetic code on master strand would have the following amino acid sequence

Glutamine----Leucine----Proline

G----T----C----A----A----T----G----C----C

Glutamine Leucine Proline

How are proteins made?

• DNA is in the cell nucleus, ribosomes (where proteins are made) are in the cell cytoplasm

• Transfer of information from nucleus to ribosomes

1. Requires another type of nucleic acid

2. It is called RNA:

RIBONUCLEIC ACID

RNA is different than DNA in many ways

• There is only 1 strand

• Has a ribose sugar

• 4 nitrogen bases are

1. Cytosine

2. Guanine

3. Adenine

4. Uracil

RNA uses the DNA as a template to read the code in order to produce the right proteins.

Three Different kinds of RNA

• m-RNA (messenger RNA)

1. Carries genetic information from DNA to ribosomes

2. Builds the physical sequence of amino acids

• t-RNA (transfer RNA)

1. Transports Amino Acids into

place.

• r-RNA (ribosomal RNA)

1. Connects the protein (amino acids) together

2. Makes up the Ribosome (with Proteins)

Transcription: Transfer of information from DNA to Ribosomes

1. DNA Molecule unzips, and unpaired bases are exposed

2. RNA NUCLEOTIDES attach to bases on one of the DNA strands (master strand)

Cytosine to guanine C—G or G—C

Adenine to uracil A—U

3. RNA nucleotides combine (develop backbone)

4. DNA reconnects and RNA is sent to the cytoplasm

Translation – Making Protein1. Using codons in m-RNA as blueprint to line

up amino acids in protein molecule

2. t-RNA molecules attach to amino acids in cytoplasm

3. Carry amino acids to Ribosomes

4. End of t-RNA molecule opposite end attached to amino acid has 3 base sequence called an anticodon

DNA and m-RNA

A T G T C A G A C G (Master DNA)

U A C A G U C U G C (m-RNA Strand)

• 3 base sequence in m-RNA is called a codon

• DNA and m-RNA molecules separate and the m-RNA molecules travel to the ribosomes

Translation continued

5. Anticodon of t-RNA match and bond to correct codon on m-RNA molecule

6. t-RNA molecules detach from m-RNA and amino acids

7. Process is repeated until whole protein molecule is produced

Errors in Stored Information

• Cells may make proteins that have amino acids in the wrong order

1. Errors are the result of change in base sequences in a DNA molecule

2. These errors are called MUTATIONS

Mutations in Reproductive Cells• Mutations affect the reproductive cells of

an organism by changing the sequence of nucleotides in a gene in the egg or sperm

• If these cells take part in fertilization, the changed gene would be part of the genetic makeup of the offspring

• This mutation may produce negative results ( death of embryo) or positive results in vary few cases ( faster or stronger individuals)

Mutations in Body Cells• If radiation hit a body cell such as your skin

tissue, this would not be passed on to your offspring. However, severe effects may result for the individual such as cancer.

• Aging is the result of a buildup of cells that do not work properly

• Some mutations effect cell division which results in cells either dividing rapidly or not dividing at all.

There are 3 types of Mutations

• Point Mutation – A change in a single base pair Ex. CAT to CAR = incorrect Amino Acid (replaced)

• Frameshift – A single base is either added or deleted. Results in an entirely new amino acid sequence. (addition or deletion)

• Chromosomal – Affect the distribution of genes to gametes during meiosis. They cause non-disjunction: the failure of chromosomes to separate

All 3 mutations will cause defective proteins to be produced

• Cells or organism with mutation will not work correctly

• Cells or organism with mutation may die

Causes of Mutations• Many occur naturally • May be influenced by the environment:

1. Chemicals

2. Ultraviolet light

3. Radiation ( large amt. of energy = bursts DNA)

4. High temperatures• Materials causing mutations are called

mutagens.

Assignment

• Mini Lab pg 306

• Do a lab write up, answer the analysis ?’s 1-3 and write a conclusion statement.

• Problem Solving lab – pg 305

• Answer the Thinking Critically Questions 1-4