lesson overview 12.1 identifying the substance of genes

Lesson Overview12.1 Identifying the

Substance of Genes

Lesson Overview Identifying the Substance of Genes

Griffith’s Experiments

Griffith isolated two different strains of the same bacterial species.

Only one of the strains caused pneumonia.

When injecting mice with disease-causing bacteria, the mice developed pneumonia and died.

When injecting mice with harmless bacteria, the mice stayed healthy.

First, Griffith took the S strain, heated the cells to kill them, and then injected the heat-killed bacteria into mice.

Mice survived, suggesting that the cause of pneumonia was not a toxin from disease-causing bacteria.

Griffith’s ExperimentsIn Griffith’s next experiment, mixed the heat-killed S-strain

with live, harmless R strain and injected the mixture into mice.

The injected mice developed pneumonia, and died.

Transformation

Process called transformation - one type of bacteria is changed permanently into another.

Because the ability to cause disease was inherited by the transformed bacteria, Griffith concluded that the transforming factor had to be a gene.

The Molecular Cause of TransformationAvery extracted molecules from heat-killed bacteria and destroyed proteins, lipids, carbohydrates, and RNA.

Transformation still occurred.

The Molecular Cause of Transformation

Then destroyed DNA and transformation did not occur.

Therefore, DNA was the transforming factor.

This led to the discovery that DNA stores and transmits genetic information.

Bacteriophages

Bacteriophage - virus that infects bacteria

The Hershey-Chase ExperimentHershey and Chase studied a bacteriophage with a DNA core and a

protein coat.

Wanted to determine if the protein coat or the DNA core entered the bacterial cell

Hershey and Chase grew viruses containing radioactive isotopes of phosphorus-32 (P-32) and sulfur-35 (S-35)

The Hershey-Chase ExperimentBacteria contained phosphorus P-32 , the marker found in DNA.

Hershey and Chase concluded that the genetic material of the bacteriophage was DNA, not protein.

Experiment confirmed Avery’s results - that DNA was the genetic material found in genes.

The Role of DNA

DNA can store, copy, and transmit genetic information

Lesson Overview12.2 The Structure of DNA

Nucleic Acids and NucleotidesLocated in the nucleus.

Made up of nucleotides, linked to form long chains.

Three components: a 5-carbon sugar called deoxyribose, a phosphate group, and a nitrogenous base.

Nucleic Acids and Nucleotides

Nucleotides joined by covalent bonds

DNA has four nitrogenous bases: adenine, guanine, cytosine, and thymine, or AGCT

Chargaff’s Rules

Chargaff discovered the percentages of [A] and [T] bases are almost equal in any sample of DNA. The same thing is true for the other two nucleotides, guanine [G] and cytosine [C].

The observation that [A] = [T] and [G] = [C] became known as one of “Chargaff’s rules.”

Franklin’s X-Rays

Rosalind Franklin used X-ray diffraction that showed:

- DNA has 2 strands that are twisted around each other.

- The nitrogen bases are near the center.

The Work of Watson and Crick

Franklin’s X-ray pattern enabled Watson and Crick to build a model of the specific structure and properties of DNA.

Built three-dimensional model of DNA in a double helix

Antiparallel Strands

DNA strands are “antiparallel”— they run in opposite directions.

Enables the nitrogenous bases to come into contact at the center.

It also allows each strand to carry nucleotides.

Hydrogen Bonding

Hydrogen bonds form between certain nitrogenous bases, holding the two DNA strands together.

Hydrogen bonds are weak forces that allow the two strands to separate.

Ability to separate is critical to DNA’s functions.

Base Pairing

Watson and Crick realized that base pairing explained Chargaff’s rule. It gave a reason why [A] = [T] and [G] = [C].

Fit between A–T and G–C nucleotides called base pairing.

12-3 D

NA REPL

EUKARYOTIC DNA REPLICATION

Step 1 – Helicase unzips the DNA molecule.

Step 2 – DNA Polymerase adds on complementary nucleotides in a 5’ to 3’ direction.

Step 3 – The lagging strand continues to replicate in fragments instead of continually like the leading strand.

Leading Strand Lagging Strand

OKAZAKI FRAGMENTS

Step 4 – Since the fragments still aren’t joined, the enzyme ligase joins the fragments.

Step 5 – As replication continues, the leading and lagging strand twist back into their helical form.

TELOMERES

Are the tips of chromosomes that make it less likely important genes will be lost with

replication.

PROKARYOTIC DNA REPLICATION

Starts at a single point, and proceeds in 2 directions until the entire chromosome is copied.

PROKARYOTIC VS. EUKARYOTIC

DNA Replication Process [3D Animation] – Biology / Medicine Animations HD

https://www.youtube.com/watch?v=27TxKoFU2Nw

Lesson Overview Fermentation

Lesson Overview13.1 RNA

The Role of RNAFirst step in decoding genetic instructions is to copy DNA into RNA.

RNA, like DNA, is a nucleic acid that consists of a long chain of nucleotides.

RNA uses the base sequence copied from DNA to produce proteins.

Comparing RNA and DNA Each nucleotide in both DNA and RNA is made up of a 5-carbon sugar, a phosphate group, and a nitrogenous base.

Three important differences between RNA and DNA:

(1) Sugar in RNA is ribose

(2) RNA is single-stranded.

(3) RNA contains uracil (U) in place of thymine (T).

Comparing RNA and DNA

The cell uses DNA “master plan” to prepare RNA “blueprints.”

DNA stays in the cell’s nucleus, while RNA goes to the ribosomes.

Functions of RNA

RNA is like a disposable copy of a segment of DNA, a working copy of a single gene.

RNA controls the assembly of amino acids into proteins.

Functions of RNA

Three main types of RNA:

messenger RNA, ribosomal RNA, and transfer RNA.

Messenger RNA

The RNA molecules that carry copies of instructions to other parts of the cell are known as messenger RNA (mRNA)

Ribosomal RNA

Ribosomal RNA (rRNA) make up ribosomes and assemble proteins.

Transfer RNA

Transfer RNA (tRNA) transfers each amino acid to the ribosome as specified by the mRNA to make proteins.

Making RNA - Transcription

Transcription – DNA serves as templates to produce complementary RNA molecules.

Transcription

In prokaryotes, RNA synthesis and protein synthesis take place in the cytoplasm.

In eukaryotes, RNA is produced in the nucleus and moves to the cytoplasm to produce proteins.

Transcription Requires RNA polymerase, which separates DNA strands, then

uses one strand of DNA as a template to assemble complementary strand of RNA.

Promoters

RNA polymerase binds to promoters - regions of DNA with specific base sequences.

Promoters show RNA polymerase where to begin making RNA.

Similar signals cause transcription to stop when a new RNA molecule is completed.

RNA Editing Portions of RNA are cut out and stay

in the nucleus are called introns.

The remaining pieces, known as exons, are spliced together to form the final mRNA, which exits the nucleus.

Lesson Overview Ribosomes and Protein Synthesis

Lesson Overview13.2 Ribosomes and

Protein Synthesis

The Genetic Code

First step in decoding genetic messages is to transcribe DNA to RNA.

Transcribed information contains a code for making proteins.

The genetic code is read three “letters” at a time, so that each “word” is three bases long and corresponds to a single amino acid.

The Genetic Code

Proteins are made by joining amino acids together into long chains, called polypeptides.

There are about 20 amino acids.

The Genetic Code

The amino acids and their order determine the properties of proteins.

Sequence of amino acids affects the shape of the protein, which determines its function.

The Genetic Code

Each three-letter “word” in mRNA is known as a codon.

A codon consists of three consecutive bases that specify a single amino acid.

Start and Stop Codons

The methionine codon AUG serves as the “start” codon for protein synthesis.

Following the start codon, mRNA is read, three bases at a time, until it reaches one of three different “stop” codons, which end translation.

Translation

The decoding of mRNA into amino acids and eventually a protein is known as translation.

Steps in Translation

mRNA is transcribed in the nucleus and then translated in the cytoplasm.

Translation begins when a ribosome attaches to mRNA.

As the ribosome reads each codon of mRNA, it directs tRNA to bring the amino acid to the ribosome.

Each tRNA molecule carries one amino acid.

In addition, each tRNA has three unpaired bases, called the anticodon — which is complement to one mRNA codon.

The ribosome forms a peptide bond between the amino acids

At the same time, the bond holding tRNA to its amino acid is broken.

The polypeptide chain grows until the ribosome reaches a “stop” codon.

When it reaches a stop codon, it releases both the newly formed polypeptide and the mRNA molecule, completing translation.

The Roles of tRNA and rRNA in Translation

rRNA holds ribosomal proteins in place and locates the beginning of mRNA.

They may even join amino acids together.

The Molecular Basis of Heredity

Genes contain instructions for assembling proteins.

The Molecular Basis of Heredity

Gene expression - the way DNA, RNA, and proteins put genetic information into action in living cells.

The Molecular Basis of HeredityThere is a near-universal nature in the genetic code.

Although some organisms show slight variations in the amino acids assigned to particular codons, the code is always read three bases at a time and in the same direction.

Despite their enormous diversity in form and function, living organisms display remarkable unity at life’s most basic level, the molecular biology of the gene.

Lesson Overview13.3 Mutations

Types of Mutations

Now and then cells make mistakes in copying their own DNA, inserting the wrong base or even skipping a base as a strand is put together.

These variations are called mutations

Mutations are heritable changes in genetic information.

Types of Mutations

All mutations fall into two basic categories:

Gene mutations - produce changes in a single gene

Chromosomal mutations - produce changes in whole chromosomes.

Gene Mutations

Point mutations - involve changes in one or a few nucleotides.

If a gene in one cell is altered, the alteration can be passed on to every cell that develops from the original one.

Gene Mutations

Point mutations include substitutions, insertions, and deletions.

Substitutions

In a substitution, one base is changed to a different base.

Usually affect a single amino acid, and sometimes they have no effect at all.

Insertions and Deletions

Insertions and deletions are point mutations in which one base is inserted or removed.

Called frameshift mutations because they shift the “reading frame” of the genetic message and can change the protein so much that it won’t be functional.

Chromosomal Mutations Chromosomal mutations involve changes in the number or structure of chromosomes.

Can change the location of genes and the number of copies of some genes.

Four types: deletion, duplication, inversion, and translocation.

Chromosomal Mutations

Deletion involves the loss of all or part of a chromosome.

Duplication produces an extra copy of all or part of a chromosome.

Inversion reverses the direction of parts of a chromosome.

Translocation occurs when part of one chromosome breaks off and attaches to another.

Effects of Mutations

Genetic material can be altered by natural or artificial means.

Resulting mutations may or may not affect an organism, most do not.

Some mutations that affect individual organisms can also affect a species or even an entire ecosystem.

Effects of Mutations

Many mutations are produced by errors in genetic processes.

During DNA replication, an incorrect base is inserted roughly once in every 10 million bases.

Small changes in genes can accumulate over time.

Mutagens Some mutations arise from mutagens - chemical or physical agents in the environment.

Chemical mutagens include certain pesticides, plant alkaloids, tobacco smoke, and environmental pollutants.

Physical mutagens include forms of electromagnetic radiation, such as X-rays and UV light. Stress can also be a factor.

Harmful Effects

The most harmful mutations dramatically change protein structure or gene activity.

Example: Sickle Cell Disease

Beneficial Effects

Some mutations can be highly advantageous to an organism or species.

Example: Pesticide Resistance and Polyploidy

lesson overview 12.1 identifying the substance of genes

structure of dna slide

role of dna dna

dna core

genetic information

dna stores

harmless bacteria

diseasecausing bacteria

injected mice

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