1. what are the 3 components of this dna nucleotide? 2. what is the function of dna in the cell?

1. What are the 3 components of this DNA nucleotide?2. What is the function of DNA in the cell?

Genetics

DNA and Genes

DNA: The Molecule of Heredity

Contributors to DNA Discovery

Early 1950’s1st picture of DNA

taken by Rosalind Franklin

using an X-ray machine.

1953DNA structure discovered by James Watson & Francis Crick.

• “FATHERS OF DNA”

• 1962• Watson, Crick and Franklin received

Nobel Prize in Medicine.

• Deoxyribose Nucleic Acid

• DNA determines an organism’s traits

• DNA ultimately determines the structure of proteins.

– body is made up of proteins.

– body’s functions depend on proteins called enzymes.

What is DNA?What is DNA?

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

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.

• Deoxyribose is the simple sugar in DNA


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

The structure of nucleotides

• 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.

• Formed by covalent bonds

• The phosphate groups and deoxyribose molecules form the backbone of the chain.

• The nitrogenous bases stick out like the teeth of a zipper. (rungs of the ladder)


• In DNA, adenine always pairs with thymine, and guanine always pairs with cytosine.


The structure of DNAThe structure of DNA

• 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.

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

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

• copies itself in order to be passed along on chromosomes during cell division.

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

Copying DNACopying DNA

1. What parts does RNA have that DNA does not have?

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

• The sequence of nucleotides in each gene contains information for assembling the string of amino acids that make up a single protein.

Genes and ProteinsGenes and Proteins

Genes and Proteins

• Proteins make up the structure of an organism AND control all of the organism’s chemical reactions to keep it alive

Where does protein synthesis occur?

*The DNA never leaves the nucleus.

*RNA copies the DNA in the nucleus.

*RNA carries the instructions from DNA out to the ribosome.

*The protein is built on the ribosome in the cytoplasm.

•DNA in the nucleus is safe !!

•DNA in the cytoplasm can be

destroyed

• RNA is a nucleic acid.

• RNA is single stranded

RNARNA

•The sugar in RNA is ribose

• 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

• 3 types of RNA that help build proteins.

• Messenger RNA (mRNA) brings instructions from DNA in the nucleus to the cell’s factory floor, the cytoplasm.

• Ribosomal RNA (rRNA) binds to the mRNA and uses the instructions to assemble the amino acids in the correct order.

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

RNARNA

“Making RNA? …. Let’s start with

Transcription

“Making RNA? …. Let’s start with

Transcription

• Transcription is a process in which enzymes make an RNA copy of a portion of a DNA strand in the cell’s nucleus.

• Transcription results in the formation of one single-stranded RNA molecule.– DNA to mRNA

• 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.

The Genetic CodeThe Genetic Code

• 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.

• There are 64 different mRNA codons in the genetic code.


• A codon is a group of three nitrogenous bases in mRNA that code for one amino acid.

The Genetic CodeThe Genetic CodeThe Messenger RNA Genetic Code

First Letter Second Letter

UU C A G

Third Letter

UCAGUCAGUCAG

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.


Translation: From mRNA to ProteinTranslation: From mRNA to Protein

• Translation is the process of converting the information in a sequence of nitrogenous bases in mRNA into a sequence of amino acids in protein.

• Translation takes place at the ribosomes in the cytoplasm.

– mRNA to tRNA

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

• An anticodon is a sequence of three bases found on tRNA.

Amino acid

Chain of RNA nucleotides

Transfer RNA molecule

Anticondon

The role of transfer RNAThe role of transfer RNA


Ribosome

mRNA codon

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

• AUG signals the start of protein synthesis.

• Then 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


DNAi

•Triplet code

•Translation

http://www.pbs.org/wgbh/nova/body/rnai.html

http://www.pbs.org/wgbh/nova/body/rnai.html

• 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.

• A mutation is any change in a DNA sequence.

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

• Mutations can occur in the reproductive cells.

– becomes part of the genetic makeup of the offspring.

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

– May be a problem for the individual

Mutations

• 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.

• Structure = Function

The effects and types of mutations

The effects of point mutations

Normal

Point mutation

mRNA

ProteinStop

Stop

mRNA

Protein

Replace G with A

Frameshift mutations

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

• A frameshift mutation is a mutation in which a single base is added or deleted from DNA.

• A frameshift mutation shifts the reading of codons by one base.

Frameshift mutations

mRNA

Protein

Frameshift mutation

Deletion of U

• Chromosomal mutations are structural changes in chromosomes.

• When a part of a chromosome is left out, a deletion occurs

•

Chromosomal Alterations

A B C D E F G H

Deletion

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


• When part of one chromosome breaks off and is added to a different chromosome, a translocation occurs.

A B E FDCBX AWC HGGE HD F

W X Y Z Y ZTranslocation


• A mutagen is any agent that can cause a change in DNA.

• 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.

1. what are the 3 components of this dna nucleotide? 2. what is the function of dna in the cell?

Documents

dna structure

summary pages

dna replication

structure of dnabecause

picture of dna

dna discoveryearly

function of dna

dna nucleotide sequences