dna - weebly
TRANSCRIPT
DNA
Essential Question: How does the structure of the DNA molecule allow it to carry information?
Fun Website to Explore! http://learn.genetics.utah.edu/content/molecules/
DNA History
• Griffith – Experimented on mice and observed some harmless strains of bacteria could change into harmful strains. He called this transformation.
• Avery – Repeated Griffith’ experiment and discovered that DNA stores and transmits genetic information from one generation to the next.
http://nortonbooks.com/college/biology/animations/ch12a01.htm
More DNA History
• Hershey-Chase –Concluded that the genetic material in bacteria was DNA not proteins
• Watson & Crick –created the double helix model for DNA after viewing the work of Rosalin Franklin
Structure of DNA
• DNA is a polymer made up of
monomers called nucleotides.
– Backbone
• Deoxyribose Sugar and Phosphate
– Rungs of the ladder
• Nitrogenous bases
Nucleotides
• Monomers of the DNA molecule– Each nucleotide is
made up of three parts: • a 5-carbon sugar
called deoxyribose • a phosphate group • and 1 of 4 different
nitrogenous bases
Nucleotide Bonding in the DNA Molecule
• Nucleotide bonding– Covalent between the sugar,
phosphates and nitrogen base
– Hydrogen bonds between the bases of opposing nucleotides
– Nitrogenous bases can occur in any order
http://learn.genetics.utah.edu/content/molecules/builddna/
Nitrogenous Bases of Nucleotides
• 4 kinds
• Divided into two classes:
1) Purines
• 2 ring structure
• Adenine & Guanine
2) Pyrimidines
• 1 ring structure
• Thymine & Cytosine
Chargaff’s Rules – Base Pairing Rules
The proportion of :
• Adenine and Thymine is always the same
– Adenine always bonds with Thymine
• Cytosine and Guanine is always the same
– Cytosine always bonds with Guanine
• Question?– A DNA sample contains 28% Adenine– What are the %’s of Thymine, Guanine and
Cytosine?
Eukaryotes & DNA
• In Eukaryotes
–DNA is• 1000 x’s more than
prokaryotes
• located in the nucleus in the form of chromosomes
DNA Length
• Bacteria have about 1.6mm of DNA
– They are only 1.6µm in diameter
• Eukaryotes have over a meter of DNA in each cell.
– How do you stuff this all in a little cell?
DNA Packaging
• Chromatin consists of DNA and protein. • The DNA helix is wrapped around nucleosomes,
an octamer of histone proteins.
DNA Replication
• During DNA replication,
– DNA molecule separates into 2 strands
– each strand serves as a template
– new “complimentary” strands are built following the base pairing rules
• Process is “semiconservative”
• New DNA has one new strand and one original strand
How It Occurs
• DNA replication regulated by a series of enzymes– DNA polymerase is the main
enzyme
• Two jobs– Add nucleotides
– “proof read” the new strands
Replication Forks and Bubbles
• Locations where
– Nucleotides are added by DNA polymerase
– Strands separate for replication
DNA polymerase
Replication fork
Replication forkNewly made complementary strand (red)
original strand (blue)
Writing Complementary Strands
• If you start with this template strand
A T C T A A G
What is the sequence of bases on the complementary strand?
Types of Nucleic Acid
DNA RNA
• Nucleotide
Sugar – Deoxyribose Ribose
Bases – A, T, G, C A, U, G, C
• Strands 2 1
• Polymer Types 1 3
Messenger RNA (mRNA)
Ribosomal RNA (rRNA)
Transfer RNA (tRNA)
From Genotype to Phenotype
• Protein Synthesis– Process that converts genotype (gene make-up)
into phenotype (physical appearance)
• 2 Steps• 1. Transcription
literally means “to write out”
• 2. Translationliterally means “to change to another language”
Step 1 - Transcription
• genetic info in DNA is transcribed into a strand
of messengerRNA (mRNA)
– Occurs in the nucleus
– Regulated by
RNA Polymerase
Starting and Stopping mRNA
• DNA carries directions
– Promotors
• start signal for RNA polymerase
– Terminators
• stop signal for RNA polymerase
Making mRNA
• Chromosome coils loosen
• RNA polymerase (enzyme) – separates the 2 strands of DNA exposing base
pairs
– matches unattached RNA bases to their complement on the DNA strand
– Covalently bondsRNA nucleotides
Writing RNA Strands
• If you start with this DNA template strand
A T G T A C A G G
What is the sequence of bases on the mRNA strand?
Editing mRNA
• mRNA must be SPLICED
• Before leaving the nucleus– introns are removed (stay inside)
– exons are linked together (exported)
INTRONS – noncoding sections of nucleic acid
EXONS – code for proteins in nucleic acid
Alternative splicing allows for a
single gene to be used for more
than one polypeptide –
RECENT DISCOVERY
The Genetic Code
• “Language” of mRNA
– Read 3 bases at a time
– 3 bases = 1 codon = 1 amino acid
• AUGCGAUACUCGUGA
• AUGAGGUAUAGCUAA
Codons
• 64 possible codons for 20 amino acids
– 1 is the “start” codon
• AA – Methionine
– 3 are “stop” codons
• UGA, UAA, UAG
• Do not code for amino acids
From Genotype to Phenotype
Essential Question:
How does the structure of the DNA molecule allow it to carry information?
Step 2 - Translation
• The process of making proteins from mRNA
– Occurs in the cytoplasm
– Need 3 things
• mRNA, tRNA, ribosome,
free amino acids
tRNA – carries amino acids
• RNA molecule that folds into a special structure
• Each tRNA carries one type of AA
• Each has a specific anticodon that matches the mRNA codon
Translation - Begins
• Setting up the RNA / Ribosome complex
– mRNA attaches to small ribosome subunit
– tRNA with Methionine attaches to mRNA
– Large ribosome subunit attaches
Translation - Elongation
• tRNA’s continue to bring in AA
• AA bond to one another and are released from the first tRNA
• Ribosome moves along the mRNA
• Process of growing the AA chain is called elongation
Examples of protein functionsFunction Description Example
Antibody Antibodies bind to specific foreign particles, such as viruses and bacteria, to help protect the body.
Immunoglobulin G
EnzymeEnzymes carry out almost all of the thousands of chemical reactions that take place in cells. They also assist with the formation of new molecules by reading the genetic information stored in DNA.
Phenylalanine hydroxylase
MessengerMessenger proteins, such as some types of hormones, transmit signals to coordinate biological processes between different cells, tissues, and organs.
Growth hormone
Structural component
These proteins provide structure and support for cells. On a larger scale, they also allow the body to move.
Actin
Transport / storage
These proteins bind and carry atoms and small molecules within cells and throughout the body. Ferritin
Proteins can be described according to their large range of
functions in the body, listed in alphabetical order:
From Genotype to Phenotype
Essential Question:
How does the structure of the DNA molecule allow it to carry information?
12.4 Mutations
Unit Essential Question:
How does the structure of the DNA molecule allow it to carry information?
Mutations
• When mistakes are made during the copying of DNA it causes changes to the genetic material and potentially to the message
• 2 Major Types of Mutations
1) Gene Mutation
2) Chromosomal Mutation
Mutations• When mistakes are made during the copying
of DNA it causes changes to the genetic material and potentially to the message
• 2 Major Types of Mutations
1) Gene Mutation (impacts a single gene)
2) Chromosomal Mutation (impacts the whole chromosome)
Gene Mutations
• Point Mutations
– A change in a single DNA base can lead to a mutation in a single gene or a number of genes depending upon location
• 3 General Types
– Insertion
– Deletion
– Substitution may or may not cause a change
result in Frameshift Mutations
Point Mutations –Insertion and Deletion
• Insertions and deletions are referred to as Frameshift Mutations because they change the “reading frame” of the codons
Point Mutation - Substitution
• A single base is substituted
• Because of code redundancy, this sometimes results in no change to the amino acid sequence
• Therefore it may be a “silent” mutation
• Or can change the code to a STOP codon and fail to produce a protein and we call this a “nonsense” mutation
Mutations• When mistakes are made during the copying
of DNA it causes changes to the genetic material and potentially to the message
• 2 Major Types of Mutations
1) Gene Mutation (impacts a single gene)
2) Chromosomal Mutation (impacts the whole chromosome)
Chromosomal Mutations
• Changes in chromosomes can occur in 4 basic types
1) Deletion
2) Duplication
3) Inversion
4) Translocation
Polyploidy
• Sometimes ENTIRE sets of chromosomes are duplicated
• Most common in plants, but can be found in fish, insects, amphibians and reptiles
• Only one report in mammals – a rat species
• Triploids (3n) and Tetraploids (4n) are the most common forms