C11- DNA and Genes

Chapter 11

Contents

• 11-1 DNA: The Molecule of Heredity• 11-2 From DNA to Protein• Protein Synthesis video• 11-3 Genetic Changes

11-1 DNA: The Molecule of Heredity

• Genetic info in DNA controls organism’s traits

11-1 DNA: The Molecule of Heredity

• Genetic info in DNA controls organism’s traits• Determines structure of proteins built

11-1 DNA: The Molecule of Heredity

• Genetic info in DNA controls organism’s traits• Determines structure of proteins built• Hershey & Chase (1952) used radioactively tagged

viruses to infect bacteria and proved DNA is genetic material

11-1 DNA: The Molecule of Heredity

• Genetic info in DNA controls organism’s traits• Determines structure of proteins built• Hershey & Chase (1952) used radioactively tagged viruses

to infect bacteria and proved DNA is genetic material

Nucleotide Structure

• DNA polymer of repeating units called nucleotides.

Nucleotide Structure

• DNA polymer of repeating units called nucleotides.

• 3 parts– Simple sugar– Phosphate

• Phosphorus w/ 4 O – Nitrogenous base

Nucleotide Structure

• DNA polymer of repeating units called nucleotides.

• 3 parts– Simple sugar– Phosphate

• Phosphorus w/ 4 O – Nitrogenous base

• C ring w/ 1 or more N & a base

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

Nucleotides

• Join in long chains • with phosphates

connecting • to sugar of next unit • to form a backbone

Nucleotides

• Join in long chains • with phosphates

connecting • to sugar of next unit • to form a backbone • with the bases sticking

out like the teeth of a zipper.

• Adenine = Thymine• Guanine = Cytosine

Structure of DNA

• James Watson & Francis Crick (1953) unraveled the structure of DNA.

• Double Helix structure

Nucleotide Sequence

• Forms unique genetic information of organism

Nucleotide Sequence

• Forms unique genetic information of organism

• Can be used to determine evolutionary relationships between organisms

Nucleotide Sequence

• Forms unique genetic information of organism

• Can be used to determine evolutionary relationships between organisms

• Or familial relationships• DNA can identify

victims or criminals

Replication of DNA

• Copies DNA in chromosome during interphase

Replication of DNA

• Copies DNA in chromosome during interphase• Enzyme breaks the hydrogen bond between bases

Replication of DNA

• Copies DNA in chromosome during interphase• Enzyme breaks the hydrogen bond between bases• Complimentary base pairing allows duplication

Replication of DNA

• Copies DNA in chromosome during interphase• Enzyme breaks the hydrogen bond between bases• Complimentary base pairing allows duplication• Each strand is a template

11-2 From DNA to Protein

• DNA controls the production of proteins.

• Proteins are key cell structures & regulators of cell functions.

11-2 From DNA to Protein

• DNA controls the production of proteins.

• Proteins are key cell structures & regulators of cell functions.

• RNA, another nucleic acid carries out DNA’s instructions

11-2 From DNA to Protein

• DNA controls the production of proteins.

• Proteins are key cell structures & regulators of cell functions.

• RNA, another nucleic acid carries out DNA’s instructions

• Structure differs 3 ways– Single-stranded– Sugar is ribose– Uracil replaces thymine

Three Types of RNA

• Protein assembly line:• Messenger RNA (m-RNA) • Ribosomal RNA (r-RNA)• Transfer-RNA (t-RNA)

Three Types of RNA

• Protein assembly line:• Messenger RNA (m-RNA)

– Brings instructions from DNA to ribosomein the cytoplasm

• Ribosomal RNA (r-RNA)• Transfer-RNA (t-RNA)

Three Types of RNA

• Protein assembly line:• Messenger RNA (m-RNA)

– Brings instructions from DNA to ribosomein the cytoplasm

• Ribosomal RNA (r-RNA)– Reads instructions to

assemble protein by binding to m-RNA

• Transfer-RNA (t-RNA)

Three Types of RNA

• Protein assembly line:• Messenger RNA (m-RNA)

– Brings instructions from DNA to ribosomein the cytoplasm

• Ribosomal RNA (r-RNA)– Reads instructions to

assemble protein by binding to m-RNA

• Transfer-RNA (t-RNA)– Delivers amino acids for

assembly to ribosome

Transcription

• Occurs in the nucleus by enzymes copying part of the DNA– Enzyme unzips DNA– Assembles single-

strand copy

Transcription

• Occurs in the nucleus by enzymes copying part of the DNA– Enzyme unzips DNA– Assembles single-

strand copy– DNA rezips after m-

RNA detaches

Transcription

• Occurs in the nucleus by enzymes copying part of the DNA– Enzyme unzips DNA– Assembles single-

strand copy– DNA rezips after m-

RNA detaches– m-RNA leaves nucleus

by nuclear pore to enter cytoplasm

Transcription

• Occurs in the nucleus by enzymes copying part of the DNA– Enzyme unzips DNA– Assembles single-

strand copy– DNA rezips after m-

RNA detaches– m-RNA leaves nucleus

by nuclear pore to enter cytoplasm

– Carries instructions to ribosome

Translation

• Occurs in the ribosome• Process of converting

series of bases into chain of amino acids forming a protein

Translation

• Occurs in the ribosome• Process of converting

series of bases into chain of amino acids forming a protein– r-RNA reads sequence

of 3 bases (codon)

Translation

• Occurs in the ribosome• Process of converting

series of bases into chain of amino acids forming a protein– r-RNA reads sequence

of 3 bases (codon) – t-RNA anticodon

matches up with the codon from m-RNA and supplies the amino acid needed

Translation

• Occurs in the ribosome• Process of converting

series of bases into chain of amino acids forming a protein– r-RNA reads sequence

of 3 bases (codon) – t-RNA anticodon

matches up with the codon from m-RNA and supplies the amino acid needed

– Ribosome translates the next codon until finished assembling the protein

RNA & Protein Synthesis

RNA Processing

• Introns- noncoding nucleotide sequences• Exons- expressed sections of nucleotides• Enzymes cut out the introns & paste the exons

together

Genetic Code

• Amino acids are the building blocks of proteins.

• A sequence of 3 nucleotide bases code for each of the 20 amino acids.

• 64 different codons in m-RNA

• AUG start codon• UAA stop codon• All organisms use the

same genetic code.

Translating the m-RNA Code

• T-RNA leaves amino acid in position to form peptide bond with previous amino acid

Translating the m-RNA Code

• T-RNA leaves amino acid in position to form peptide bond with previous amino acid

• The ribosome continues to assemble amino acids until stop codon is reached.

Translating the m-RNA Code

• T-RNA leaves amino acid in position to form peptide bond with previous amino acid

• The ribosome continues to assemble amino acids until stop codon is reached.

• Translation is complete

Translating the m-RNA Code

• T-RNA leaves amino acid in position to form peptide bond with previous amino acid

• The ribosome continues to assemble amino acids until stop codon is reached.

• Translation is complete• Amino acid chain is

released & twists into complex folded shape of protein

Translating the m-RNA Code

• T-RNA leaves amino acid in position to form peptide bond with previous amino acid

• The ribosome continues to assemble amino acids until stop codon is reached.

• Translation is complete• Amino acid chain is

released & twists into complex folded shape of protein

• Become enzymes & structures

11-3 Genetic Changes

• Mutation- any change in DNA sequence

• Caused by errors in– Replication– Translation– Cell division– Or by external agents

such as UV or chemical exposure

Mutations in Reproductive Cells

• Changes in the sequence of nucleotides can cause:– Altered gene in offspring– New traits– Nonfunctional protein

with structural or functional problems in cells

– Embryo may not survive– Positive effect

Mutations in Body Cells

• Does not pass on to offspring

• May cause problems for the individual

• Impair function of the cell• Contributes to aging• Can cause cancer by

making cells reproduce rapidly

Effects of Point Mutations

• Point mutation - Change in a single base pair in DNA

• Can change entire structure of the protein

• Error may or may not affect protein function

• Ex. Sickle cell anemia

Frameshift Mutations

• A single base is added to or deleted from DNA

• Shifts the reading of the codons by one base

• Nearly every amino acid after the insertion or deletion will be changed

Chromosomal Alterations

• Chromosomal mutations• Deletions -Parts break &

are lost during mitosis or meiosis

• Insertions- Parts rejoin incorrectly

• Inversions- Rejoin backwards

• Translocations- Join other chromosomes

• Common in plants

Causes of Mutations

• Mutagens- agents that cause change in DNA– Radiation

• X-rays• Gamma rays• Ultraviolet light• Nuclear radiation

– Chemicals• Dioxins• Asbestos• Benzene• Formaldehyde

– High temperaturesaflatoxinaflatoxin

6-legged frog6-legged frog

Repairing DNA

• Repair mechanisms have evolved:

• Enzymes proofread DNA & replace incorrect nucleotides.

• The greater the exposure to the mutation, the less likely it can be corrected.

• Limit exposure to mutagens.