DNA AND PROTEIN SYNTHESIS. DNA (DEOXYRIBONUCLEIC ACID) Nucleic acid that is found in chromosomes and carries genetic information.

DNA AND PROTEIN SYNTHESIS

DNA (DEOXYRIBONUCLEIC ACID)

• Nucleic acid that is found in chromosomes and carries genetic information.

Watson and Crick• Chargaff

• Rosalind Franklin & Maurice Wilkins (crystalline x-ray diffraction patterns)

CHROMOSOME ORGANIZATION

1. A chromosome is an enormous strand of super coiled DNA.

2. Sections of DNA on the chromosome that code for proteins are called genes.

3. Noncoding sections of DNA are called “junk DNA”

http://www.allaboutscience.org/junk-dna.htm

BUILDING BLOCKS OF DNA

Composed of nucleotides

• Nucleotides contain three parts:

1. 5-Carbon Sugar (deoxyribose)

2. Phosphate Group

3. Nitrogen Base (four types, adenine, guanine, thymine and cytosine)

• Adenine and Guanine are purines (composed of two rings of nitrogen atoms)

• Thymine and Cytosine are pyrimidines (composed of one ring of nitrogen atoms)

STRUCTURE OF DNA

• Consists of two strands of nucleotides that form a twisted ladder (double helix)

• Sugar and phosphate alternate along the sides of the ladder (linked by strong covalent bonds)

• Pairs of nitrogen bases form the rungs of the ladder (linked by weak hydrogen bonds).

• Specific base pairing arrangement (Chargaff’s Rule)

A-T : 2 hydrogen bonds

C-G : 3 hydrogen bonds

• Nitrogen bases attach to the sugar portion of the side (NOT the phosphate)

• Strands run in opposite directions

FUNCTION OF DNA

• DNA codes for proteins (structural proteins, enzymes, and hormones)

• information for building proteins is carried in the sequence of nitrogen bases

• proteins determine physical and metabolic traits and regulate growth and development.

Packaged

• DNA and protein is packed together to form chromatin.

• Chromatin is DNA that is coiled around circular proteins called histones.

DNA REPLICATION

Process in which DNA is copied

PURPOSE OF DNA REPLICATION

Gives daughter cells produced by cell division a complete set of genetic information identical to the parent cell.

WHERE REPLICATION OCCURS

Nucleus

WHEN DURING THE CELL CYCLE REPLICATION OCCURS

Interphase (S)

HOW REPLICATION OCCURS

1. Helicase enzymes unzip the parent strand by separating the nitrogen base pairs.

2. DNA polymerase pairs free DNA nucleotides with the exposed bases on both strands following the base pair rules.

• each strand from the parent molecule serve as a template

3. Hydrogen bonds reform spontaneously sealing the two strands of each DNA molecule together.

DNA polymerase also proofreads each new DNA strand to make sure there are no mistakes.

RESULTS OF REPLICATION

• Two molecules of DNA that are identical

• Each is half old (strand from parent) and half new (strand synthesized by DNA polymerase)

RNA (RIBONUCLEIC ACID)

Nucleic acid involved in the synthesis of proteins

RNA STRUCTURE

Composed of nucleotides, but differs from DNA in three ways.

1. Single strand of nucleotides instead of double stranded

2. Has uracil instead of thymine

3. Contains ribose instead of deoxyribose

RNA FUNCTION

Three forms of RNA involved in protein synthesis

1. mRNA (messenger): copies instructions in DNA and carries these to the ribosome.

2. tRNA (transfer): carries amino acids to the ribosome.

3. rRNA (ribosomal): composes the ribosome.

PROTEIN SYNTHESIS

Cells build proteins following instructions coded in genes (DNA).

• Consists of two parts, transcription and translation

TRANSCRIPTION

DNA is copied into a complementary strand of mRNA.

WHY?

• DNA cannot leave the nucleus. Proteins are made in the cytoplasm. mRNA serves as a “messenger” and carries the protein building instructions to the ribosomes in the cytoplasm.

LOCATION OF TRANSCRIPTION

Nucleus

HOW TRANSCRIPTION OCCURS

1. RNA polymerase untwists and unzips a section of DNA (usually a single gene) from a chromosome.

2. RNA polymerase pairs free RNA nucleotides to the exposed bases of one of the DNA strands following base pair rules.

• Uracil replaces thymine

• Only 1 strand of DNA serves as a template, the other “hangs out”

3. Newly synthesized mRNA separates from template DNA and DNA zips back up.

RESULT OF TRANSCRIPTION

mRNA strand with instructions for building a protein that leaves the nucleus and goes to the cytoplasm.

TRANSCRIPTION EXAMPLE

• Transcribe the following DNA Sequence in mRNA pg. 303

TAC CGG ATC CTA GGA TCA

AUG GCC UAG GAU CCU AGU

PROTEINS

Structural and functional components of organisms.

• Composed of amino acids

• order of nucleotides in DNA determines order of amino acids in a protein

• One gene codes for one protein

GENETIC CODEThe “language” that translates the sequence

of nitrogen bases in DNA (mRNA) into the amino acids of a protein.

• Codon = three nucleotides on DNA or mRNA

• One codon specifies one amino acid• Some codons are redundant (code for the

same amino acid)• The genetic code is universal to all

organisms

DNA: TAC CTT GTG CAT GGG ATC

mRNA AUG GAA CAC GUA CCC UAG

A.A MET G.A HIS VAL PRO STOP

IMPORTANT CODONS

• AUG = start translation (Met)

• UAA, UAG, UGA= stop translation

TRANSLATION

Instructions in mRNA are used to build a protein

LOCATION OF TRANSLATION

ribosome (in the cytoplasm)

PROCESS OF TRANSLATION

1. mRNA binds to the ribosome.

2. Ribosome searches for start codon (AUG)

3. tRNA brings correct amino acid (methionine) to the ribosome.

• Each tRNA carries one type of amino acid. • The anticodon (three nitrogen bases on

tRNA) must complement codon for amino acid to be added to protein chain

4. ribosome reads next codon

5. tRNA’s continue lining up amino acids according to codons

6. peptide bonds link amino acids together

7. ribosome reaches STOP codon

• Amino acid chain is released

http://www.pbs.org/wgbh/aso/tryit/dna/shockwave.html

RESULT OF TRANSLATION

A Protein

http://www.courses.fas.harvard.edu/~biotext/animations/TRANSLATE20b.swf

http://highered.mcgraw-hill.com/sites/0072437316/student_view0/chapter15/animations.html#

End of sec. 1-3

Chapter 12

Electrophoresis

• Technique for molecular separation.

• Molecules are separated in a gel.

• The gel is placed in an electrical field.

• Like charges repel, unlike charges attract.

What is DNA Profiling?

A technique used by scientists to distinguish between individuals of the

same species using only samples of their DNA

Who Invented it?

• The process of DNA fingerprinting was invented by Alec Jeffreys at the University of Leicester in 1985.

• He was knighted in 1994.

Stages of DNA Profiling

• Stage 1:

Cells are broken down

to release DNA

If only a small amount of DNA is available it can be amplified using the polymerase chain reaction (PCR)

Stages of DNA Profiling

• Step 2: The DNA is cut into fragments using restriction enzymes.

Each restriction enzyme cuts DNA at a specific base sequence.

Stages of DNA Profiling

• The sections of DNA that are cut out are called restriction fragments.

• This yields thousands of restriction fragments of all different sizes because the base sequences being cut may be far apart (long fragment) or close together (short fragment).

Stages of DNA Profiling

Stage 3:• Fragments are

separated on the basis of size using a process called gel electrophoresis.

• DNA fragments are injected into wells and an electric current is applied along the gel.

Stages of DNA Profiling

DNA is negatively charged so it is attracted to the positive end of the gel.

The shorter DNA fragments move faster than the longer fragments.

DNA is separated on basis of size.

Stages of DNA Profiling

• A radioactive material is added which combines with the DNA fragments to produce a fluorescent image.

• A photographic copy of the DNA bands is obtained.

Stages of DNA Profiling

Stage 4:

• The pattern of fragment distribution is then analysed.

Uses of DNA Profiling

• DNA profiling is used to solve crimes and medical problems

Crime

• Forensic science is the use of scientific knowledge in legal situations.

• The DNA profile of each individual is highly specific.

• The chances of two people having exactly the same DNA profile is 30,000 million to 1 (except for identical twins).

Biological materials used for DNA profiling

• Blood• Hair• Saliva• Semen• Body tissue cells• DNA samples have been

obtained from vaginal cells transferred to the outside of a condom during sexual intercourse.

DNA Profiling can solve crimes

• The pattern of the DNA profile is then compared with those of the victim and the suspect.

• If the profile matches the suspect it provides strong evidence that the suspect was present at the crime scene (NB:it does not prove they committed the crime).

• If the profile doesn’t match the suspect then that suspect may be eliminated from the enquiry.

Example

• A violent murder occurred.

• The forensics team retrieved a blood sample from the crime scene.

• They prepared DNA profiles of the blood sample, the victim and a suspect as follows:

Was the suspect at the crime scene?

Suspects Profile

Blood sample from crime scene

Victims profile

Solving Medical Problems

DNA profiles can be used to determine whether a particular person is the parent of a child.

A childs paternity (father) and maternity(mother) can be determined.

This information can be used in• Paternity suits• Inheritance cases• Immigration cases

Example: A Paternity Test

• By comparing the DNA profile of a

mother and her child it is possible to

identify DNA fragments in the child

which are absent from the mother and

must therefore have been inherited

from the biological father.

Is this man the father of the child?

Mother Child Man

Famous Cases

• Colin Pitchfork was the first criminal caught based on DNA fingerprinting evidence.

• He was arrested in 1986 for the rape and murder of two girls and was sentenced in 1988.

• Electrophoresis Virtual Lab