Unit #5 - Instructions for Life: DNAmrpbiology.weebly.com/uploads/2/7/5/6/2756971/dna... · DNA DNA stores and transmits genetic information from one generation to the next. Years

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Unit #5 - Instructions for

Life: DNA

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Introduction

On the following slides, the blue sections are the most important.

Underline words = vocabulary!

All cells carry instructions for life – DNA.

In this unit, we will study the basic shape of DNA and learn how the molecule DNA carries instructions for life.

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DNA Lab Reflections What did you learn during the

this week’s DNA extraction lab?

What surprised you?

How can this science help

society?

DNA extraction has improved

with modern science. View the

video clip to understand how

crime investigators collect DNA

samples from evidence.

Video

http://flowtv.org/wp-content/uploads/2007/11/csi3.jpg

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DNA – Cell Review

Video

Link

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Instructions Within Cells All cells have genetic

material known as

DNA (deoxyribonucleic

acid).

In prokaryotes, the

DNA is loose within the

cell.

In eukaryotes, DNA is

held within the

nucleus.

Regardless of where the DNA is contained in the cells, the

instructions for every part of an organism come from the

molecule DNA.

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DNA DNA stores and transmits genetic

information from one generation to the

next.

Years of research has

lead scientists to begin to

understand how DNA

works.

DNA is made up of

strings of nucleotides.

Sketch it!

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DNA = Strings of Nucleotides

DNA nucleotides, or

nucleic acids are made

up of 3 basic

components:

– A five-carbon sugar

called deoxyribose

– A phosphate group

– A nitrogen base (A, T,

C, or G)

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Basic Structure of DNA The sugar/phosphate backbone

makes up the outside of the DNA

molecule.

There are four nitrogen bases

that make up the middle of DNA.

They are…

– Adenine: this base always

pairs with thymine

– Guanine: this base always

pairs with cytosine

The bases are connected by a

hydrogen bond.

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Chargaff’s Rules An American biochemist, Erwin Chargaff, studied the

structure of DNA.

Chargaff’s rules state that within the DNA molecule, the percentage (or amount of) of guanine always matches the percentage of cytosine (they always pair together).

Likewise, the %T= %A.

G-CAT rule (straight letters together and curvy letters together)

http://bcs.whfreeman.com/thelifewire/content/chp11/f11005.gif

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Nucleotide Hands

With a pen:

– Write a “P” on

your thumb

– “S” on your palm

– Write an “A” on

your 1st finger

– “G” = 2nd finger

– “C” = 3rd finger

– “T” = pinkie

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1. A’s pair with T’s

2. G’s pair with C’s

3. Sugars with the

Bases

4. Phosphates are free!

Memory

Tool

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DNA Writing Prompt

What is DNA?

Add details to your prompt from

last week:

– The shape?

– The components (or parts)?

– The pattern?

– Draw a picture for extra credit!

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DNA Structure Chart

Backbone Center

Nucleotides

Sugar

Phosphate

Nitrogenous

Base

a a

a X

X X

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DNA’s History:

Franklin’s XRays In the early 1950’s,

Rosalind Franklin (a woman!) studied the structure of DNA using X-rays.

Franklin’s X-rays eventually led to the discovery that the strands of DNA are twisted around each other in a shape much like the coils of a spring, known as a helix.

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Franklin's X-ray

diffraction

photograph of

DNA, 1953

Photo: Courtesy

HarperCollins

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DNA’s History: Watson &

Crick’s Model Around the same time

Franklin was researching DNA, two other scientists James Watson and Francis Crick were also studying DNA.

They built 3-D models to show the shape of DNA using wire and cardboard.

Watson and Crick’s model of DNA was a double helix, where 2 strands of DNA twist around each other.

http://itcamp.teacher.org.hk/2009CU1/GEN5/files/images/dnastructure.jpg

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Reconstruction of Crick

and Watson’s 1953

molecular model of DNA,

using the original

components.

© Science Museum/Science

and Society Picture Library

The Model That Started it All

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DNA Quick Fact

If you took the DNA found in every

cell of the human body and

stretched it out, it would be 610

million km long. You could travel

from Earth to the sun and back –

twice!

http://www.louisville.edu/a-

s/english/dale/105/watson/Jurrasic%20park%20DNA.g

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Practice Creating the Code

Pick up a white board and marker from the

front.

Practice making the complimentary DNA

strand using the following code.

A G C T A G C

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Practice Creating the Code

Pick up a white board and marker from the

front.

Practice making the complimentary DNA

strand using the following code.

A C T G A T A

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DNA

Replication DNA contains instructions for every cell of an organism.

It, therefore, needs to be copied (or replicated) for each new cell to function properly.

The design of DNA makes it easy to copy!

Using the “G-CAT” rule, half a strand of DNA can easily create the complimentary strand!

DNA replication is when a cell duplicates its DNA.

http://bio.usuhs.mil/dna_replication2.gif

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Replication Fork

During DNA replication, the strand separates into two strands forming a replication fork.

Enzymes (specifically DNA polymerase & helicase) help during replication and unzip the DNA molecule to create the fork.

This can occur spontaneously at multiple points along the DNA strand until the entire strand has been copied.

http://www-

math.mit.edu/~lippert/18.417/lectures/01_Intro/Pictures/100000000000014A0

00001507D945A01.png

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DNA Polymerase

DNA polymerase travels down the strand, reading each nitrogen base (A,T,C or G) and using molecules made within the cell, builds the new strand.

Remember, A always with T, C always with G! (G-CAT)

Each DNA molecule to go through replication has one “old” strand and one “new” strand.

Video

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Semi Conservative Model (of

DNA Replication)

The Semi-conservative model of DNA replication statest that each DNA molecule to go through replication has one “old” strand and one “new” strand.

Video

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The Central Dogma

DNA RNA PROTEIN

Replication

Transcription Translation

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Genes Contained with DNA

The DNA within cells

is contained within

chromosomes in the

nucleus.

Sections of the DNA

strand code for

specific information,

called genes.

Genes code for

specific traits (EX

brown eyes, skin color,

or blood type).

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Genes Code for Proteins The genes within a cell’s

DNA code for instructions, but instructions for what?

The instructions in DNA are instructions for making proteins.

Proteins (large molecules) are involved in many biological functions, from making up our skin, hair, and muscles, to fighting the common cold.

DNA makes the proteins that create you! http://images.clinicaltools.com/images/gene/codon.jpg

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RNA

DNA is held within the nucleus of each cell.

mRNA (or messenger ribonucleic acid) carries a copy of the genetic code to make proteins at the ribosomes (rRNA) of the cell.

http://www.biologycorner.com/resources/mRNA-colored.gif

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RNA cont. RNA is composed of:

– sugar called ribose

– a phosphate group

– and nitrogenous base

– “U-A G, C”

– Uracil (replaces Thymine) in RNA

RNA is single stranded, not double like DNA

There are three types of RNA (mRNA, tRNA, and rRNA).

http://www.accessexcellence.org/RC/

VL/GG/images/rna.gif

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Practice Creating the Code

Pick up a white board and marker from the

front.

Practice making the complimentary RNA

strand using the following code.

A C T G A T A

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Practice Creating the Code

Pick up a white board and marker from the

front.

Practice making the complimentary RNA

strand using the following code.

A C T G A T A

U G A C U A U

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Messenger RNA

Messenger (mRNA) is one type of

RNA that carries DNA “message”

out of nucleus to the ribosome.

mRNA is created in the nucleus in

the process called transcription (or

the process of copying genetic

information from DNA into mRNA).

Transcription happens in the

nucleus.

http://www.tokyo-med.ac.jp/genet/mutation/nort.gif

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Making mRNA

If the DNA code reads like this…

ATC-GTA-CGC-AAT-TGC

…Then the mRNA code reads like this…

UAG-CAU-GCG-UUA-ACG

A = U

G = C

The enzyme RNA polymerase separates two strands

of a DNA double helix and builds a strand of RNA

using RNA nucleotides (A, U, C, G).

Remember, RNA is a single strand.

The creation of RNA is called transcription.

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Transfer RNA or tRNA

Transfer (tRNA) RNA carries

amino acids to the ribosome

where the proteins are built.

A tRNA molecule is a single

strand of RNA that loops back

on itself.

One looped end of the tRNA

has a codon that matches the

mRNA codon.

The other end carries an

amino acid. http://ghs.gresham.k12.or.us/science/ps/sci/ibbio/chem/nuclei

c/chpt15/tRNA.gif

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Translation The ribosome is an

organelle in the cell

which builds proteins.

The mRNA carries the

“code” (or instructions)

to the ribosome.

The ribosome reads

the strand three bases

at a time.

Three base pairs

(called a codon or a

triplet; EX “AUG”) code

for a specific amino

acid; amino acids make

up proteins.

http://www.chesterfield.k12.sc.us/Cheraw%20Intermediate/DaveEvans/Biolog

yICP/Protein%20Synthesis.jpg

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Protein Synthesis Video

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RNA Codons Molecules called amino acid chains make up proteins.

Some codons do not code for amino acids, but signal a ribosome to either “start” or “stop” copying the strand.

There is only one “start” codon (AUG) that can begin the process (methionine).

UAA, UAG and UGA are 3 stop codons (like a period at the end of a sentence) which tell the ribosome the protein is complete.

http://genetics.gsk.com/graphics/codon.gif

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AA Chart An amino acid chart

helps to translate codons.

Start at the center and pick a letter.

Move to the next level and pick another letter.

Finally move to the outside and the three letters (a “codon”) match up to an amino acid (found on the outside!).

Practice: GGA codes for….?

http://bioephemera.com/wp-content/uploads/2007/03/image003.jpg

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Translation occurs when the cell uses the genetic information in mRNA to build proteins.

Translation is done at the ribosome (the site of protein synthesis).

mRNA comes from the nucleus and binds to the ribosome.

the “start” codon AUG signals the beginning of a protein.

tRNA molecules carry specific amino acids from around the cytoplasm to the ribosome.

As each tRNA molecule arrives with an amino acid, it links it to the previous amino acid that was dropped off there, forming a long chain.

Translation = Building a Protein

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Protein Synthesis Animation

(a protein)

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Protein Synthesis

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All cells (prokaryotes & eukaryotes) contain DNA!

The role of DNA is like the “master plan” that a builder would use to construct a house.

The role of RNA is like the inexpensive blueprints that are taken to the construction site (mRNA & tRNA).

The DNA (master plan) must be stored safely in the nucleus while RNA can leave the nucleus to go to the protein-building site.

The protein building site is the ribosome.

In Conclusion

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