Unit 8DNA

EQ1:What is the

shape, structure

and function of

DNA?

DNA• Deoxyribonucleic Acid

• A form of nucleic acid–One of the four biological

macromolecules• Remember: Carbohydrates, Proteins, Lipids and Nucleic Acids

–Stores information within the cell, to code for proteins

• Nucleic Acids are composed of Nucleotides.

Nucleotides

Nucleotides• Composed of:

–Deoxyribose (A 5-carbon sugar)–Phosphate Group–Nitrogen Base

Nitrogen Bases• Ring-shaped

• Contain Nitrogen

• DNA has four possible nitrogen bases: – Adenine– Guanine– Cytosine– Thymine

Nitrogen Bases

• Adenine pairs up with Thymine.

• Cytosine pairs up with Guanine.

The Double Helix• Nucleotides combine to form two long

chains that intertwine with each other. • Appears as a spiral ladder, or double

helix.

The Double Helix• Nitrogen bases are held together by

weak hydrogen bonds. • The “sides” of the ladder are

composed of deoxyribose and phosphate groups.

The Function of DNA • DNA contains the unique genetic code

or organisms within the code of the nucleotides.

EQ2:What is

DNA Replication

?

Mitosis

Review: DNA during the Cell Cycle

• Interphase: DNA replicatesMitosis:• Prophase: Chromatin coils and

thickens to form chromosomes. • Metaphase: Chromosomes move to

the center of the cell.• Anaphase: Sister chromatids are

pulled to opposite poles during anaphase.

• Telophase: Two identical cells are formed.

Review: DNA during the Cell Cycle• Interphase: DNA replicates

Meiosis:• The cell will divide twice, instead of

once so that the chromosome number is reduced by half.

• Four haploid (1/2 chromosomes) cells form.–Each contains a different set of

alleles, leading to increased genetic variation and diversity, essential for the organism to adapt to changing environments.

DNA Replication

DNA Replication• DNA cannot leave the nucleus of the cell

where it is stored because it is too large to pass through the pores of the nuclear membrane.

• During replication, enzymes “unzip” the two strands of the DNA molecule by breaking the hydrogen bonds that hold the base pairs together.

• Each strand serves as a template for the attachment of complementary bases.

DNA Replication continued…

• Then, another enzyme zips up the two new DNA molecules.

• The two new molecules are identical, each containing one of the parent strands and one newly made daughter strand.

• When the cell replicates, the nuclear membrane disintegrates and each new daughter cell receives an identical copy of the parent cell’s DNA.

DNA Replication

EQ3:What is the structure

and function of

RNA?

RNAStructur

e

DNA vs. RNA

RNA• Ribonucleic Acid• Like DNA, it is a form of nucleic acid• Unlike DNA, it can leave the nucleus of the cell.

– This enables RNA to carry the information from the DNA to the ribosomes during the process of transcription.

• Nucleic Acids are composed of Nucleotides.– RNA Nucleotides are a single strand composed

of:• Sugar: Ribose• Phosphate Group• 4 Nitrogen Bases:

Adenine, Guanine, Cytosine and Uracil– Uracil replaces Thymine

DNA vs.

RNA

Three Types

of RNA

Three Types of RNA • RNA helps to build proteins.1. Messenger RNA (mRNA): Takes the

message from the DNA in the nucleus and carries it to the ribosomes.

2. Ribosomal RNA (rRNA): Makes up the ribosomes.

3. Transfer RNA (tRNA): Transports the amino acids to the ribosomes to be assembled into proteins.

EQ4:What is

transcription?

Transcription• Proteins are

synthesized at the ribosomes from the DNA code.

• Since DNA is stored in the nucleus, a message with the DNA’s code is transcribed and sent instead.

Transcription1. During transcription an enzyme bind to a

promoter site and “unzips” the two strands of the DNA molecule by breaking the hydrogen bonds that hold the base pairs together.

2. One strand serves a template for the attachment of complementary bases. However, not all the DNA is transcribed; just the instructions for the protein that is being synthesized.

3. The single stranded copy of the DNA called messenger RNA (mRNA) exits the nucleus through the pores in the nuclear membrane and makes its way to the ribosome.

EQ5:What is

translation?

Translation• The mRNA strand serves as the instructions for the

sequence of amino acids that make the protein.

• Each three base sequence of mRNA is called a codon.

• Each codon specifies a particular amino acid.

• A transfer RNA (tRNA) molecule “transfers” the specified amino acid from the cytoplasm to the ribosome.

• Because tRNA molecules have the complementary bases to the codon (called an anti codon) on one end of it, they can bind with the mRNA codons.

Translation continued…• The other end of the molecule carries the amino acid

that is specified by the codon.

• The next amino acid is brought by another tRNA molecule and as the tRNA anti-codons bind with the codons on the mRNA the amino acids are bonded to each other forming the protein chain.

• When a stop codon is reached, the protein is released and coils up in the structure that will allow it to perform its function.

EQ6:What is the role of DNA

in gene expression?

DNA/Gene Expression• An expressed gene is a gene that has been

transcribed into RNA.

• Only a fraction of the genes in a cell are expressed at any given time.

• Certain DNA sequences serve as promoters and binding sites for the RNA polymerase (enzyme).

• Regulation of gene expression is important in shaping the way a complex organism develops from a single fertilized egg.

•  

EQ7:What are

mutations?

Mutations• Def: Changes to the genetic code caused by

errors in DNA replication.

• Occur in both somatic (body) cells or gamete (reproductive) cells.

• When mutations occur in gamete cells, they can be passed on to subsequent generations

EQ8:What are

the causes and

consequences of gene

mutations?

Point Mutation/Sickle Cell Anemia

Point Mutations• Point mutations affect one nucleotide.

• If one nucleotide is substituted for another, only

one amino acid is altered.

• This may or may not affect the functioning of the protein, because several codons can code for the same amino acid.

• Even the substitution of one amino acid for another may not affect the function of the protein.

• May be spontaneous or caused by mutagens

Frame Shift Mutation• A nucleotide is deleted or inserted.

• Every amino acid after that point will be affected because every codon will be changed.

• Such mutations often alter a protein so that it is unable to perform its normal functions.

Frame Shift Mutation/Tay Sachs

EQ9:What

mutagenic factors exist

in the environment and what effect do

they have?

Mutagens• Def: An agent that can cause a change in

the DNA sequence that in turn affects the expression of a gene.

• Environmental mutagens: – Tobacco – Radiation: Nuclear or UVB

• Only if such mutations occur in gamete cells can they be passed down from one generation to another.

EQ10:What is genetic

engineering?

Genetic Engineering• Process that makes changes in the DNA code of

living organisms. • A DNA fragment containing the wanted gene is

joined to a vector which is used to transfer the gene into the host organism.

• It has been used to engineer bacteria that can break down pollutants into harmless products, and other bacteria that can produce medicines, such as human growth hormone and insulin.

• Transgenic animals have been created that are used to study diseases and the role genes play in an organism.

• Plants have been engineered to resist herbicides and to produce internal pesticides.

• Gene therapy has been used to successfully treat SCID.

EQ11:What is

DNA Sequencing

?

DNA Sequencing• Process used to find the nucleotide base sequence in

pieces of DNA.

• A complementary DNA strand is made using a small proportion of fluorescently labeled nucleotides, which stops the replication process.

• The DNA is then separated using electrophoresis and the DNA sequence can be read from the gel. – It is generally an automated process in labs

presently. – It has been used in the Human Genome Project

and – Used to identify genes responsible for genetic

disorders such as Alzheimer’s disease

EQ12:What is PCR?

PCR• Polymerase chain reaction is a process used to

make multiple copies of genes. • Using primers to start the replication process,

DNA is heated to separate the 2 strands. • It is then cooled to allow the replication process. • This process is repeated for multiple copies. • In forensics, it has been used to amplify the

amount of DNA found at a crime scene. • In medicine, it has been used to simplify the DNA

from a single embryonic cell for rapid diagnosis of genetic disorders.

• It is also used to identify infective agents and genes that cause disorders such as hemophilia and cystic fibrosis.

EQ13:What is gel

electrophoresis?

Gel Electrophoresis• Procedure used to separate and analyze

DNA fragments.

• Mixture of DNA fragments are placed at the end of a porous gel.

• An electrical voltage is applied to the gel to separate the fragments.

• DNA fingerprinting has been used to determine paternity and to identify the DNA at crime scenes.

Unit 8DNA

The End