Objective: We will be able to describe the basic process of DNA replication and how it relates to the transmission and conservation of the genetic material

Objective:Objective:We will be able to describe the We will be able to describe the basic process of DNA basic process of DNA replication and how it relates replication and how it relates to the transmission and to the transmission and conservation of the genetic conservation of the genetic material. SC.912.L16.3material. SC.912.L16.3

• Although the environment influences how an organism develops, the genetic information that is held in the molecules of DNA ultimately determines an organism’s traits.

• DNA achieves its control by determining the structure of proteins.

What is DNA?What is DNA?

• All actions, such as eating, running, and even thinking, depend on proteins called enzymes.• Enzymes are critical for an organism’s function because they control the chemical reactions needed for life.

What is DNA?What is DNA?

• Within the structure of DNA is the information for life—the complete instructions for manufacturing all the proteins for an organism.

• In 1952 Alfred Hershey and Martha Chase performed an experiment using radioactively labeled viruses that infect bacteria.

• These viruses were made of only protein and DNA.

DNA as the genetic materialDNA as the genetic material

• Hershey and Chase labeled the virus DNA with a radioactive isotope and the virus protein with a different isotope.

DNA as the genetic materialDNA as the genetic material

• By following the infection of bacterial cells by the labeled viruses, they demonstrated that DNA, rather than protein, entered the cells and caused the bacteria to produce new viruses.

• DNA is a polymer made of repeating subunits called nucleotides.

• Nucleotides have three parts: a simple sugar, a phosphate group, and a nitrogenous base.

Phosphate group

Sugar (deoxyribose)

Nitrogenous base

The structure of nucleotidesThe structure of nucleotides

• The phosphate group is composed of one atom of phosphorus surrounded by four oxygen atoms.

• The simple sugar in DNA, called deoxyribose (dee ahk sih RI bos), gives DNA its name—deoxyribonucleic acid.


• A nitrogenous base is a carbon ring structure that contains one or more atoms of nitrogen.

• In DNA, there are four possible nitrogenous bases: adenine (A), guanine (G), cytosine (C), and thymine (T).

Adenine (A) Guanine (G) Thymine (T)Cytosine (C)


• Thus, in DNA there are four possible nucleotides, each containing one of these four bases.


• Nucleotides join together to form long chains, with the phosphate group of one nucleotide bonding to the deoxyribose sugar of an adjacent nucleotide.

• The phosphate groups and deoxyribose molecules form the backbone of the chain, and the nitrogenous bases stick out like the teeth of a zipper.


• In DNA, the amount of adenine is always equal to the amount of thymine, and the amount of guanine is always equal to the amount of cytosine.


• In 1953, Watson and Crick were the first to suggest that DNA is the shape of a double helix.

The structure of DNAThe structure of DNA

• Watson and Crick also proposed that DNA is shaped like a long zipper that is twisted into a coil like a spring.

• Because DNA is composed of two strands twisted together, its shape is called double helix.

The importance of nucleotide sequencesThe importance of nucleotide sequences

Chromosome

The sequence of nucleotides forms the unique genetic information of an organism. The closer the relationship is between two organisms, the more similar their DNA nucleotide sequences will be.

The importance of nucleotide sequencesThe importance of nucleotide sequences

• Scientists use nucleotide sequences to determine evolutionary relationships among organisms, to determine whether two people are related, and to identify bodies of crime victims.

Replication of DNAReplication of DNA

• Before a cell can divide by mitosis or meiosis, it must first make a copy of its chromosomes.

• The DNA in the chromosomes is copied in a process called DNA replication.

• Without DNA replication, new cells would have only half the DNA of their parents.

Replication of DNA

Replication of DNA

DNA

Replication

Replication

Replication of DNA

Replication of DNA

Click this image to view movie

• DNA is copied during interphase prior to mitosis and meiosis.

• It is important that the new copies are exactly like the original molecules.

Copying DNACopying DNA

Replication of DNAReplication of DNA Student Notebook p. 104 Student Notebook p. 104

1. DNA unzips at the bases breaking the hydrogen bonds.

2. Nucleotides that are floating free in the cell attach to the unzipped chains of DNA.

3. The molecule continues to unzip and base pairs continue to match and join by hydrogen bonding.

4. Two new strands of DNA will be formed containing an old and new strand.

Copying DNACopying DNA

Original DNA

Original DNA

Strand

Original DNA

Strand

Free Nucleotides New DNA

moleculeNew DNA

Strand

New DNA molecule

• The sequence of nucleotides in DNA contain information.

Genes and ProteinsGenes and Proteins

• This information is put to work through the production of proteins.

• Proteins fold into complex, three- dimensional shapes to become key cell structures and regulators of cell functions.

The pairing of nitrogenous The pairing of nitrogenous bases in DNA is the key bases in DNA is the key feature that allows DNA to be feature that allows DNA to be copied.copied.

Objective:Objective:We will be able to Explain the We will be able to Explain the basic processes of basic processes of transcription and translation, transcription and translation, and how they result in the and how they result in the expression of genes. expression of genes. SC.912.L.16.5SC.912.L.16.5

• Some proteins become important structures, such as the filaments in muscle tissue.

• Other proteins, such as enzymes, control chemical reactions that perform key life functions—breaking down glucose molecules in cellular respiration, digesting food, or making spindle fibers during mitosis.


> By encoding the instructions for making proteins, DNA controls cells.

> DNA is the template for instruction on how to make a gene turn into part of the individual

> In fact, enzymes control all the chemical reactions of an organism.


• You learned earlier that proteins are polymers of amino acids.

• RNA molecule is a polymer composed of subunits called nucleotides.


• RNA like DNA, is a nucleic acid. RNA structure differs from DNA structure in three ways.

• First, RNA is single stranded—it looks like one-half of a zipper —whereas DNA is double stranded.

RNARNA

• The sugar in RNA is ribose; DNA’s sugar is deoxyribose.

Ribose

RNARNA

• Both DNA and RNA contain four nitrogenous bases, but rather than thymine, RNA contains a similar base called uracil (U).

• Uracil forms a base pair with adenine in RNA, just as thymine does in DNA.

Uracil

Hydrogen bonds Adenine

RNARNA

• DNA provides workers with the instructions for making the proteins, and workers build the proteins.

• The workers for protein synthesis are RNA molecules.

RNARNA

• DNA provides workers with the instructions for making the proteins, and workers build the proteins.

• The workers for protein synthesis are RNA molecules.

• They take from DNA the instructions on how the protein should be assembled, then—amino acid by amino acid—they assemble the protein.

RNARNA

• There are three types of RNA that help build proteins.

• Messenger RNA (mRNA), brings instructions from DNA in the nucleus to the cytoplasm – ribosome.

• On the factory floor, mRNA moves to the assembly line, a ribosome.

RNARNA

• Ribosomes are made of proteins and rRNA (ribosomal). Ribosomes is the site for protein synthesis. This is where the gene will be expressed.

• The ribosome, made of ribosomal RNA (rRNA), binds to the mRNA and uses the instructions to assemble the amino acids in the correct order.

RNARNA

• Transfer RNA (tRNA) is the supplier. Transfer RNA delivers amino acids to the ribosome to be assembled into a protein.

RNARNA

Click image to view movie

TranscriptionTranscription

Transcription is the process in the cell nucleus where a copy of RNA is made from part of a DNA strand.



• The main difference between transcription and DNA replication is that transcription results in the formation of one single-stranded RNA molecule rather than a double-stranded DNA molecule.

• Not all the nucleotides in the DNA of eukaryotic cells carry instructions—or code—for making proteins.

• Genes usually contain many long noncoding nucleotide sequences, called introns, that are scattered among the coding sequences.

RNA ProcessingRNA Processing


• Regions that contain information are called exons because they are expressed.

• When mRNA is transcribed from DNA, both introns and exons are copied.

• The introns must be removed from the mRNA before it can function to make a protein.

• Enzymes in the nucleus cut out the intron segments and paste the mRNA back together.

• The mRNA then leaves the nucleus and travels to the ribosome.


Explain how and why the Explain how and why the genetic code is universal and genetic code is universal and is common to almost all is common to almost all organisms. SC.912.L.16.9organisms. SC.912.L.16.9

• The nucleotide sequence transcribed from DNA to a strand of messenger RNA acts as a genetic message, the complete information for the building of a protein.

• As you know, proteins contain chains of amino acids. You could say that the language of proteins uses an alphabet of amino acids.

The Genetic CodeThe Genetic Code

• Biochemists began to crack the genetic code when they discovered that a group of three nitrogenous bases in mRNA code for one amino acid. Each group is known as a codon.

• A code is needed to convert the language of mRNA into the language of proteins.


• Sixty-four combinations are possible when a sequence of three bases is used; thus, 64 different mRNA codons are in the genetic code.

• Anticodon – tRNA triplet of nitrogenous base that bond to codon (mRNA)


The Genetic CodeThe Genetic CodeThe Messenger RNA Genetic Code

First Letter Second Letter

UU C A G

Third Letter

UCAGUCAGU

CAG

UCAG

C

A

G

Phenylalanine (UUU)

Phenylalanine (UUC)

Leucine (UUA)

Leucine (UUG)

Leucine (CUU)

Leucine (CUC)

Leucine (CUA)

Leucine (CUG)

Isoleucine (AUU)

Isoleucine (AUC)

Isoleucine (AUA)

Methionine;Start (AUG)

Valine (GUU)

Valine (GUC)

Valine (GUA)

Valine (GUG)

Serine (UCU)

Serine (UCC)

Serine (UCA)

Serine (UCG)

Proline (CCU)

Proline (CCC)

Proline (CCA)

Proline (CCG)

Threonine (ACU)

Threonine (ACC)

Threonine (ACA)

Threonine (ACG)

Alanine (GCU)

Alanine (GCC)

Alanine (GCA)

Alanine (GCG)

Tyrosine (UAU)

Tyrosine (UAC)

Stop (UAA)

Stop (UAG)

Histadine (CAU)

Histadine (CAC)

Glutamine (CAA)

Glutamine (CAG)

Asparagine (AAU)

Asparagine (AAC)

Lysine (AAA)

Lysine (AAG)

Aspartate (GAU)

Aspartate (GAC)

Glutamate (GAA)Glutamate (GAG)

Cysteine (UGU)

Cysteine (UGC)

Stop (UGA)

Tryptophan (UGG)

Arginine (CGU)

Arginine (CGC)

Arginine (CGA)

Arginine (CGG)

Serine (AGU)

Serine (AGC)

Arginine (AGA)Arginine (AGG)

Glycine (GGU)

Glycine (GGC)Glycine (GGC)

Glycine (GGA)

Glycine (GGG)

• Some codons do not code for amino acids; they provide instructions for making the protein.

• More than one codon can code for the same amino acid.

• However, for any one codon, there can be only one amino acid.


• All organisms use the same genetic code.

• This provides evidence that all life on Earth evolved from a common origin.


Translation: From mRNA to ProteinTranslation: From mRNA to Protein

• The process of changing the information in the mRNA into an amino acids chain is known as translation.

• Translation takes place at the ribosomes in the cytoplasm.

• In prokaryotic cells, which have no nucleus, the mRNA is made in the cytoplasm.

Translation: From mRNA to ProteinTranslation: From mRNA to Protein

• In eukaryotic cells, mRNA is made in the nucleus and travels to the cytoplasm.

• In cytoplasm, a ribosome attaches to the strand of mRNA like a clothespin clamped onto a clothesline.

• For proteins to be built, the 20 different amino acids dissolved in the cytoplasm must be brought to the ribosomes.

• This is the role of transfer RNA.

The role of transfer RNAThe role of transfer RNA

• Each tRNA molecule attaches to only one type of amino acid.

Amino acid

Chain of RNA nucleotides

Transfer RNA molecule

Anticondon


TranslationTranslation


Ribosome

mRNA codon

• Usually, the first codon on mRNA is AUG, which codes for the amino acid methionine.

• AUG signals the start of protein synthesis.

• When this signal is given, the ribosome slides along the mRNA to the next codon.


tRNA anticodon

Methionine


• A new tRNA molecule carrying an amino acid pairs with the second mRNA codon.

Alanine


• The amino acids are joined when a peptide bond is formed between them.

AlanineMethionine

Peptide bond


• A chain of amino acids is formed until the stop codon is reached on the mRNA strand.

Stop codon


Explain how mutations in the DNA sequence may or may not result in phenotypic change. Explain how mutations in gametes may result in phenotypic changes in offsprings. SC.912.L.16.4

• Organisms have evolved many ways to protect their DNA from changes.

Mutations

• In spite of these mechanisms, however, changes in the DNA occasionally do occur.

• Any change in DNA sequence is called a mutation.

• Mutations can be caused by errors in replication, transcription, cell division, or by external agents.

• Mutations can affect the reproductive cells of an organism by changing the sequence of nucleotides within a gene in a sperm or an egg cell.

Mutations in reproductive cells

• If this cell takes part in fertilization, the altered gene would become part of the genetic makeup of the offspring.

Mutations in reproductive cells

• The mutation may produce a new trait or it may result in a protein that does not work correctly.

• Sometimes, the mutation results in a protein that is nonfunctional, and the embryo may not survive.

• In some rare cases a gene mutation may have positive effects.

• What happens if powerful radiation, such as gamma radiation, hits the DNA of a nonreproductive cell, a cell of the body such as in skin, muscle, or bone?

• If the cell’s DNA is changed, this mutation would not be passed on to offspring.

• However, the mutation may cause problems for the individual.

Mutations in body cells

Mutations in body cells

• Damage to a gene may impair the function of the cell.

• When that cell divides, the new cells also will have the same mutation.

• Some mutations of DNA in body cells affect genes that control cell division.

• This can result in the cells growing and dividing rapidly, producing cancer.

• A point mutation is a change in a single base pair in DNA.

• A change in a single nitrogenous base can change the entire structure of a protein because a change in a single amino acid can affect the shape of the protein.

The effects of point mutations

The effects of point mutations

Normal

Point mutation

mRNA

ProteinStop

Stop

mRNA

Protein

Replace G with A

Frameshift mutations

• What would happen if a single base were lost from a DNA strand?

• This new sequence with the deleted base would be transcribed into mRNA. But then, the mRNA would be out of position by one base.

• As a result, every codon after the deleted base would be different.


mRNA

Protein

Frameshift mutation

Deletion of U


• This mutation would cause nearly every amino acid in the protein after the deletion to be changed.

• A mutation in which a single base is added or deleted from DNA is called a frameshift mutation because it shifts the reading of codons by one base.

• Changes may occur in chromosomes as well as in genes.

• Alterations to chromosomes may occur in a variety of ways.

• Structural changes in chromosomes are called chromosomal mutations.

Chromosomal Alterations

• Chromosomal mutations occur in all living organisms, but they are especially common in plants.

• Few chromosomal mutations are passed on to the next generation because the zygote usually dies.


• In cases where the zygote lives and develops, the mature organism is often sterile and thus incapable of producing offspring.

• Deletion is when a part of a chromosome is left out.

Deletion

A B C D E F G H A B C E F G H


• When part of a chromatid breaks off and attaches to its sister chromatid, an insertion occurs.

• The result is a duplication of genes on the same chromosome.

Insertion

A B C D E F G H A B C B C D E F G H


• When part of a chromosome breaks off and reattaches backwards, an inversion occurs.

Inversion

A B C D E F G H A D C B E F G H


• Translocation is when part of one chromosome breaks off and is added to a different chromosome.

A B E FDCBX AWC HGGE HD F

W X Y Z Y ZTranslocation


• Some mutations seem to just happen, perhaps as a mistake in base pairing during DNA replication.

• These mutations are said to be spontaneous.

• However, many mutations are caused by factors in the environment.

Causes of Mutations

• Any agent that can cause a change in DNA is called a mutagen.

• Mutagens include radiation, chemicals, and even high temperatures.

• Forms of radiation, such as X rays, cosmic rays, ultraviolet light, and nuclear radiation, are dangerous mutagens because the energy they contain can damage or break apart DNA.

Causes of Mutations

Causes of Mutations• The breaking and reforming of a double-

stranded DNA molecule can result in deletions.

• Chemical mutagens include dioxins, asbestos, benzene, and formaldehyde, substances that are commonly found in buildings and in the environment.

• Chemical mutagens usually cause substitution mutations.

Repairing DNA• Repair mechanisms that fix mutations in cells

have evolved.

• Enzymes proofread the DNA and replace incorrect nucleotides with correct nucleotides.

• These repair mechanisms work extremely well, but they are not perfect.

• The greater the exposure to a mutagen such as UV light, the more likely is the chance that a mistake will not be corrected.

• Alfred Hershey and Martha Chase demonstrated that DNA is the genetic material.

DNA: The Molecule of Heredity

• Because adenine can pair only with thymine, and guanine can pair only with cytosine, DNA can replicate itself with great accuracy.

DNA: The Molecule of Heredity

• DNA, the genetic material of organisms, is composed of four kinds of nucleotides. A DNA molecule consists of two strands of nucleotides with sugars and phosphates on the outside and bases paired by hydrogen bonding on the inside. The paired strands form a twisted-zipper shape called a double helix.

• Genes are small sections of DNA. Most sequences of three bases in the DNA of a gene code for a single amino acid in a protein.

From DNA to Protein

• Messenger RNA is made in a process called transcription. The order of nucleotides in DNA determines the order of nucleotides in messenger RNA.

From DNA to Protein

• Translation is a process through which the order of bases in messenger RNA codes for the order of amino acids in a protein.

Genetic Changes

• A mutation is a change in the base sequence of DNA. Mutations may affect only one gene, or they may affect whole chromosomes.

• Mutations in eggs or sperm affect future generations by producing offspring with new characteristics. Mutations in body cells affect only the individual and may result in cancer.

PedigreePedigree – A graphic – A graphic representation of an representation of an individual’s family treeindividual’s family tree

Patterns of Heredity Patterns of Heredity

Incomplete Dominance Incomplete Dominance is is when the phenotype of when the phenotype of heterozygous individuals is heterozygous individuals is intermediate between those intermediate between those two homozygotes. Example: two homozygotes. Example: Snapdragon plantsSnapdragon plants

Codominant Alleles Codominant Alleles causes the causes the phenotypes of both phenotypes of both homozygotes to be produced homozygotes to be produced in heterozygous individuals. in heterozygous individuals. Example Roan cattle contains Example Roan cattle contains both red and white hairs. both red and white hairs.

Multiple Alleles Multiple Alleles are traits that are traits that are controlled by more than are controlled by more than two alleles. Blood type is an two alleles. Blood type is an example. A, B, AB, Oexample. A, B, AB, O

Polygenic Inheritance Polygenic Inheritance The The inheritance pattern of a trait inheritance pattern of a trait controlled by two or more controlled by two or more genes. Example – coat color of genes. Example – coat color of an arctic fox – three genes an arctic fox – three genes control the coat color.control the coat color.

Sex-linked traits Sex-linked traits are traits that are are traits that are controlled by genes located on the controlled by genes located on the X or Y chromosomes. Example X or Y chromosomes. Example

End of Chapter 11 Show

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Objective: We will be able to describe the basic process of DNA replication and how it relates to the transmission and conservation of the genetic material