The Molecule of Heredity

The Molecule of Heredity

Chapter 12 (pg. 342)

The Roles of DNADNA has three jobs in heredity:

1. STORES instructions for cell functions and protein production.

2. COPY itself exactly. (so that it can be transferred correctly to offspring)

-This process is called replication. -Enzymes control the process.

3. TRANSMIT genetic information and pass it along during cell division.

Chromosomes

• A chromosome is one of the threadlike "packages" of genes and other DNA in the nucleus of a cell (in eukaryotes).

• Prokaryotes don’t have a nucleus so DNA is floating in the cytoplasm

• Different kinds of organisms have different numbers of chromosomes.

Gene• functional & physical unit of heredity

passed from parent to offspring.

• Genes are pieces of DNA

• Contain the information for making a specific protein.

Genome

• All the DNA contained in an organism or a cell

Includes:

– chromosomes

– DNA in mitochondria

– DNA in the chloroplasts of plant cells

DNA Structure• Deoxyribonucleic acid.

• Monomer = Nucleotide

• These strands each have a nitrogenous base connected to them and those base pairs meet in the middle

• The strands twist around one another forming a double helix– (described & discovered by Watson, Crick &

Franklin)

DNA Structure: Nucleotides

• 5 carbon sugar – deoxyribose

• Phosphate group

• Nitrogen base (4)

–Adenine

–Guanine

–Cytosine

– Thymine

• Hydrogen bonds hold the two DNA strands together where the nitrogen bases meet

• The sides of the DNA ladder are composed of alternating sugar and phosphate and are called “backbones”

DNA Structure

Types of Nitrogen Bases

Purines –have two ringsin their structure

– Adenine

– Guanine

Pyrimidines –have one ring in their structure

- Thymine - Cytosine

Nitrogen Base PairingBases pair in a

specific pattern…

A purine always bonds to a pyrimidine

Adenine bonds to thymine.

Guanine bonds to cytosine.

True or False?

• Because of base pairing in DNA, the percentage of pyrimidines is about equal to the number of purines.

What Pairs with What?

What does adenine (A) pair with?

Thymine (T)

What does cytosine (C) pair with?

Guanine (G)

http://www.ncbi.nlm.nih.gov/

Cytosine and Thymine are what type of nitrogen bases?

Purine or pyrimidine?

Answer: Pyrimidine!!!

• Note: All three words have a “Y” in them.

Check Yourself• Which of these is a

purine?

• Which picture does not show/include a nitrogenous base?

• Which structure would attract a cytosine molecule?

RNAChapter 13 (pg. 362)

RNA is just as cool as DNA!!!

What is RNA?• Ribonucleic Acid

• Makes copies of DNA instructions to site of protein production

• DNA is the master blueprint, RNA are the portable copies.

3 Types of RNA1. mRNA

• Messenger RNA

• Carries instructions from the DNA to the ribosomes, where protein production occurs.

• mRNA is made from a DNA strand, in a process called “transcription”.

A U G U

3 Types of RNA (cont.)2. rRNA

• Ribosomal RNA

• Makes the Ribosome– Along with proteins

rRNA

3 Types of RNA (cont.)

3. tRNA

• Transfer RNA

• Transfers amino acids to the ribosome where “translation” occurs, and matches amino acids to the mRNA strand.

Types of Nitrogen Bases

Purines –have two ringsin their structure

– Adenine

– Guanine

Pyrimidines –have one ring in their structure

- Uracil- Cytosine

No “T” in RNA!

DNA vs. RNA

DNA- Sugar: deoxyribose

- Double stranded

- Nitrogen bases:A C G T

- “Master Blueprint”

RNA- Sugar: ribose

- Single stranded

- Nitrogen bases:A C G U

- “Blueprint Copies”

Crashcourse: DNA and Replication

DNA ReplicationDNA is copied in a process called “replication”.

1. DNA “unzips” down its H-bonds usingan enzyme called helicase

2. The two half strands then act as a template for the production of two new strands

Replication Fork

If this is a template strand, what complementary strand would it

make?

-A C T G G--T G A C C-

3. Another enzyme, (DNA Polymerase) usesbase pairing rules match new base pairs onto each strand.

• Now, each new DNA molecule has one old strand of nucleotides and one new strand.

Protein Synthesis

Protein Synthesis• Process of turning the instructions found in

DNA into working proteins.

• Step 1: Transcription

• Step 2: Translation

Transcription• DNA is coded, and needs to be delivered and read

in order to make proteins.

• We can make a messenger RNA (mRNA) in the process called “transcription” that will travel to the ribosomes carrying a copy of the DNA’s information.

Transcription (cont.)• First, the DNA helix separates

like it did in replication.

• But this time each template strand will base pair with RNA’s nitrogen bases:

A C G U

– Cytosine with Guanine

– Adenine with Uracil

(not Thymine anymore!)

• Bases are put together by the enzyme: RNA Polymerase

• This new single mRNA strand will leave the nucleus and make it’s way to the ribosome.

Transcribe this strand:

-A C T G A--U G A C U-

The story so far:

-DNA has been transcribed into the form of mRNA

-The mRNA has travelled from the nucleus to the Ribosome.

Now what?

What message is contained in the mRNA?

Why did the cell do all this?

RNA : Translation

Translation:when the cell uses information from mRNA to produce proteins.

• Happens in the ribosome

• tRNA translates the code on the mRNA to an amino acid – tRNA is a ‘middle man’ – Amino acid on one side, and

an anticodon that matches up with a codon from mRNA

ANTICODON

tRNA

mRNA

How is mRNA read?

• The mRNA strand is read in:Codons: sets of 3 bases

How many codons are in this strand of mRNA?

AUGCCAGCAUACUUACAUUGA =

7! AUG | CCA | GCA |UAC | UUA | CAU |UGA

Starts reading at the “start” codon:

AUGStops reading at the “stop” codon:

UAA, UAG, UGA

Step 1

Messenger RNA is transcribed in the nucleus and then enters the cytoplasm.

Nucleus

mRNA

CYTOPLASM

A U G U U C A A A

Why doesn’t the mRNA stay in the nucleus????

Where is it going???

Step 2

• Happens at the ribosomes

• Translation begins at the start codon (AUG)

• tRNA comes in, and basepairs to the mRNA.

• Each tRNA contains 3 bases (anticodon) that tell it where to attach on the mRNA.

tRNAAmino Acid

A

A A A

A A A

U

U U U

C

CG

G

Ribosome

mRNAStrand

Anticodon

Codon

StartCodon

Step 3

• The ribosome bonds the amino acids together.

• After tRNA drops off its amino acid, the mRNA releases the tRNA.

• New tRNA brings the next amino acid in.

tRNA

A

A A

A A AU U U

U

CG

G

mRNACodon

U U

Amino acids

Step 4

• The process continues, building the polypeptide chain, until the tRNA meets a “stop” codon.

• Once it reaches a “stop” codon, the polypeptide chain is released.

Polypeptide chain

ribosome

tRNA

mRNA

What’s our end product

here?

What did we make?

Let’s see Translation in action!!!!

So now we have a polypeptide chain…or a PROTEIN!

Scientists need to be able to tell proteins apart sometimes….can you think of a reason why?

In order to tell proteins apart we need to know the names of all the amino acids that make them up!

To find out which amino acid is being translated, take the mRNA codon that is being translated and find it in the chart.

•AUG: (Start) Methionine •UCU: Serine•ACC: Threonine•CGA: Arginine•UAG: STOP

Naming Amino Acids

mRNA Strand:AUGUCUACCCGA

You try!!!!!Naming Amino Acids

mRNA Strand: AUGGAGACCUCGCCCUAG

You try!!!!!Naming Amino Acids

AUGGAGACCUCGCCCUAG

•AUG: (Start) Methionine •GAG: Glutamic Acid•ACC: Threonine•UCG: Serine•CCC: Proline•UAG: STOP

Summary

Process Function Location

DNAReplication

Copying DNA,making two complementary strands.

Nucleus (stays in nucleus)

RNA Transcription

Using DNA to make a copy of mRNA.

Nucleus (sends to ribosomes)

Translation

Using the mRNA we made to decode DNA’s message and make proteins.

Ribosomes

Pro

tein

Syn

thes

is

Quick Review!

Check Yourself

• Identify structure F

Check Yourself

• From which labeled structure is structure D made? Identify that labeled structure.

Check Yourself

• What is structure E?

Check Yourself

• What is structure D?

Check Yourself

• Which letter represents the process of translation?

Check Yourself

• Which letter represents the process of transcription?

Steps of Protein SynthesisPut the below in order:

A. The completed polypeptide is released from the ribosome.

B. The ribosome joins the amino acids together and releases the tRNAmolecules.

C. Transfer RNA brings an amino acid to the ribosome and binds to its codon.

D. Messenger RNA is transcribed from DNA and moves to the ribosome.

D, C, B, E, A

Check Yourself

Where does the above process take place?

Check Yourself

Label the structures involved with protein synthesis

Mutations

Mutations

Occasionally, cells make mistakes when copying their DNA.

• If the base pairs don’t stay in the correct order, a mutation can occur

• Mutation: when DNA is damaged or changed in such a way that alters the genetic message

carried by that gene.

• Gene Mutations: mutations that change a single gene

• Chromosomal Mutations: mutations that change whole chromosomes.

There are two different types of mutations:

Gene Mutations

• Gene mutations that involve a change in onenucleotide are called point mutations.

–Occur at a single “point”

–Usually happen during replication.

–3 different kinds of point mutations:

1. Substitution

2. Insertion

3. Deletion

1. Substitution

• One nitrogen base is changed to a different nitrogen base.

– Usually only affects one amino acid, or sometimes have no effect at all.

Ex:

CCC CCA CCC ACCProline Proline Proline threonine

Frameshift Mutations.

Insertions and deletions can make dramatic changes in the DNA sequence. Another name

for them is: frameshift mutations.

• Shifting changes the codons, therefore changing the amino acids (proteins).

2. Insertions

• When one nitrogen base is inserted into the DNA sequence.– The effect can be dramatic, changing the amino

acid sequence from that point on.

CGACCCATT CGA CCC ATT

CGACTCCATT CGA CTC CAT T

3. Deletions

• When one nitrogen base is deleted out of the sequence

– Effect can be dramatic, affecting all the amino acids after the deletion.

CCGTACAGG CCG TAC AGG

CCGTACAGG CCG ACA GG__

Chromosomal Mutations• Involve changes in whole chromosome.

Four types:

• Deletion-Missing a base

• Duplication-Two bases where one should be

• Inversion-Reversing base positions

• Translocation-Set of bases where they don’t belong

Why do mutations happen?

Mutations happen for multiple reasons:

– Error in genetic replication

– Stressful environments

– Mutagens: chemical or physical agents in the environment (ex: tobacco smoke)

Harmful effects of mutations

• Cancers • Diseases

• Sickle cell disease- Mutations

affect the shape of red blood cells.

Benefits of mutations

In some cases, mutations benefit certain organisms

• Insects that (over time) are able to resist chemical pesticides

• Farmers also use genetically modified plants that are genetically mutated to be bigger and fuller crop.

Check Yourself

Name the type of mutation:

1. TAC GGC AGC TGATAC GCG CAG CTG

2. A B C D E FA B C D D E F

3. AAC TGA CGC GACAAC TGA CGC TAC

Insertion

Duplication

Substitution

Are these point or chromosomal mutations? Point

Check Yourself

Name the type of mutation:

Deletion

Duplication

Inversion

Translocation

Bacteria Evolving Antibiotic Resistance

All organisms need to grow

• We know that cells come from preexisting cells

• This means that cells will begin to grow until they start to divide!

• Living things grow by producing MORE cells!

• What obstacles do cells face when they start to grow????

• As a cell becomes larger, it places more demand on its DNA.

• Living cells store all their important information in the DNA. As a cell gets bigger, the DNA does not.

• Large cells have trouble making copies of it’s DNA

• As a cell becomes larger in volume, it’s surface area can’t keep up.

• Ex: As you blow up a balloon,you’re increasing the volume (overall size), but the cell membrane (the rubber balloon) can’t keep up and gets stretched thinner and thinner.

• Since the cell is enlarged, food and water get used up much quicker.

• Waste is produced much faster.

• The cell has a harder time moving enough materials across its cell membrane

• Before it gets too big, a cell will DIVIDE!

• This forms two “daughter” cells.

• They’re called daughter cells because each cell gets a complete copy of the DNA.

2 Types of Cells

1)BODY(somatic) CELLS

2) SEX CELLS (gametes)

2 Types of CellsDiploid:

Two copies of each chromosome.

Body Cells

Haploid:One copy of each chromosome

Sex cells

• There are two types of reproduction:

• Asexual: producing a genetically identical offspring from a single parent.

• Sexual: produces offspring that share genetic information of two parents.

Sexual Reproduction• Takes more time to find a

mate.

• Favorable for seasonal environments.

• Provides genetic diversity

• Multicellular organisms

• Meiosis

Asexual Reproduction• Favorable for faster

reproduction when conditions are right.

• Genetically identical offspring helps when conditions are favorable

• Single –celled organisms

• Mitosis

Meiosis

• Sexual reproduction

• Gamete production

• Sperm and Egg

• Contain half the regular number of chromosomes (Haploid)

Mitosis

• Body cell copying

• Asexual Reproduction

• Cells make exact copies of themselves

• Contain full sets of chromosomes (Diploid)

• During the cell cycle, the parent cell (having 2 chromosomes in the diagram) will produce two daughter cells (each containing 2 chromosomes in the diagram)

Body Cells• Body cells are all cells other than

sex cells– Also called somatic cells– Made by mitosis

• Body cells are diploid cells: they have 2 copies of every chromosome. (Think di = 2)

• Their chromosomes each have a matching chromosome (homologous pairs)

What is the diploid number of chromosomes in humans?

46!

23 pairs!

Sex Cells• Also called gametes

• Eggs and sperm

• Made by meiosis

• Have haploid number of cells (N)

Humans =23

What is meiosis?• Asexual reproduction(relies on mitosis): all of the

parents DNA gets copied and goes to the offspring.

• Sexual reproduction(relies on meiosis)

Meiosis is cell division to form gametes (sex cells)

–Sperm: male gamete

–Egg: female gamete

Meiosis 1: Prophase 1• Homologous Chromosomes

pair up in Prophase I.

• Crossing-Over: Sister chromatids cross over one another and exchange genes.– HAPPENS ONLY IN PROPHASE I

of Meiosis

• Does not make identical daughter cells due to shuffled genes in crossing-over

Crossing over example

Which letter would result from a single crossover of the above homologous pair?

• A human sperm cell (gamete) has a haploid (N) number of chromosomes = 23.

• Once a haploid egg (N) is fertilized by a sperm it is called a

zygote.

• The diploid (2N) number of chromosomes in a human zygote = 46.

Fertilization

Egg = haploid (N) Sperm = haploid (N)

ZYGOTE =diploid (2N)

Humans 23 + 23 =46

Fertilized egg

Cell Differentiation

Regulatory Genes

• Allow for cell differentiation in eukaryotes

• A sort of “on off switch” for gene expression

Regulatory Genes

• Hox Genes:

– Lay out the basic body forms of many animals, including humans, flies, dogs and worms.

– They set up the head-to-tail organization. (What goes where and in what order)