DNA - The Code Of Life

What units make up DNA?

A DNA molecule is a long chain (polymer) made up of many small units (monomers) ie. building blocks called nucleotides. Each nucleotide contains: a. A sugar molecule (deoxyribose) b. A phosphate molecule c. A nitrogenous base - Adenine - Thymine - Guanine - Cytosine

Selection of Proteins

A protein is a long chain of small units called amino acids. There are twenty two different amino acids involved in protein synthesis. These may combine in different numbers and different sequences to form 1000s of different proteins. The shortest protein consists of 50 amino acids. Order in which amino acids are linked determine what protein is made. Amino acids as are linked by means of peptide bonds.

Mitochondrial DNA Testing

A scrape of tissue is taken from the inside of ones cheek and is sent to a lab. Genetic code is studied and compared to mitochondrial DNA of others or a reference sample in the lab. This reference sample is called the Cambridge Reference Sequence, a source of information of mitochondrial DNA commonly found in the people of European decent.

Antibiotics and its Influence on Protein Synthesis

Antibiotics are produced to contract bacterial infections. They do this by interacting with bacterial ribosomes and inhibiting protein synthesis. Ribosomes of bacteria and of the host are vastly different so that the antibiotic cannot target the host. Proteins are essential for the growth of new cells, therefore they cannot spread infection. TYPES: a. Tetracyclines - prevent attachment of tRNAs carrying amino acids. b. Chloramphenicol - prevent formation of peptide bonds.

DNA Fingerprinting

Comparing of genetic profiles: - from same person to show identical bonding patterns. - in related people = some similar parts. - in unrelated people = different pattern. NB: DNA is a stable molecule. DNA can be collected from long-dried blood, semen, and even bones of ancient Neanderthals and still be okay to use in investigations.

How is DNA Profiled?

DNA is extracted from the tissue. DNA is cut in repeat sections by restriction enzymes. Fragments are multiplied using PCR. Combinations of different lengths of repeats differ for every person. Sections are experimentally separated into groups (large to small). That is each persons DNA fingerprint.

Role of DNA

DNA molecules: - carry hereditary information in the form of genes. - provide a blueprint for organisms growth by coding for protein synthesis. - can replicate, so that a copy of genetic information is passed onto each daughter cell formed during cell division. This ensures that genetics are passed down through generations.

Why is DNA Replication Important?

DNA needs to produce an exact replica of itself in order to ensure that the genetic code is passed onto each new daughter cell formed during cell division.

Genetic Replication

Discovered by Watson and Crick. Pairing of bases suggested that when given a sequence of bases in one strand, the other strand was automatically determined. After they created the double helix model, people still had questions. In 1961, Crick and Brenner showed the triplet code. They showed that form is function: a double molecule can replicate and carry genetic instructions.

Genetic Links with Mitochondrial DNA

During fertilization, only chromosomes from the sperm cell enter the egg cell. Therefore, the resultant zygote comes from the mother. Mitochondrial DNA can be used to establish a direct maternal genetic line. Mitochondrial DNA mutates occasionally. eg - substitution takes place where one nucleotide is replaced by another, resulting in a marker. Mitochondrial DNA can be mapped through generations, which enables researchers to trace lineages through females. All females in the family therefore have the same mitochondrial DNA.

DNA Profiling

Each person has unique DNA in their cells. The differences occur in the highly variable, non-coding DNA. DNA profiling involves the extracting and identifying of non-coding DNA. Non-coding DNA contains repeating sequences of base pairs called STRs. (Short Tandem Repeats). At the same point in DNA in different people, the number of repeats varies considerably, and this is how we distinguish between different peoples DNA. 13-20 different sites are investigated, enough to show a unique profile for that individual. Variation of genetic sequence is used to generate a DNA profile of the individual. Genetic sequence can be found in blood, bone, hair, tissue, etc. DNA PROFILE: unique DNA fragments of an individual, separated by electrophoresis.

Bases

Foundation of the genetic code, instructing cells on how to synthesize enzymes and proteins. Four different nucleotides, each containing a sugar and phosphate molecule with a different nitrogenous base.

Nucleic Acids

Have the capacity to store onformation that controlla cellular activity. Controls th synthesis of proteins. Ultimately control structure and the function of living organisms.

Discovery

In the early 1950s, Rosalind Franklin and Maurice Wilkins researched DNA by X-Ray Crystallography. James Watson and Francis Crick researched Franklin and Wilkins findings. They built a model out of brass plates and clamps and realized that DNAs structure is much like a twisted ladder, with two runners (sugar and phosphate) and a series of rungs (made of parts of organic compounds)

Where is DNA?

Mainly found in the nucleus of the cell where it forms an important part of chromosomes making up the chromatin network. Chromatin = chromosomal material that is made up of DNA, RNA and histone proteins as found in a non-dividing cell. DNA molecule is coiled so that the long structures can fit inside the nucleus.

Types of RNA

Messenger RNA Transport RNA Ribosomal RNA THEY ALL MAKE PROTEINS.

Why do we have Mitochondrial DNA?

Mitochondria formed a symbiotic relationship with eukaryotic cells through endosmosis.

Differences in Organisms

Nucleotides are the same in ALL organisms. The sequence in which the nucleotides as strung together make the difference. ie - ACCTGA is to AGTCCA like "post" is to "pots". The letters may be the same, but they're two completely different things. The sequence in one human is different to everyone else (except in identical twins). It is, therefore, the sequence of bases that determines the genetic code of an organism.

Non-Coding DNA

Only 2% of DNA actually codes for proteins. Protein coding regions are called exons, they are interrupted by non-coding regions called introns. The more non-coding DNA an organism has, the more complex it is. Non-coding DNA are not junk, and are known to form functional RNA molecules with regulatory functions. THEDOGRA-DGSHSJ-NANDATET-SHEYJEM-HECAT exons intron exon intron exon

How is DNA a Double Helix?

Outer two strands are formed by a chain of alternating sugar/phosphate links. These bonds are strong. Rings are formed by pairs of bases linked by weak Hydrogen Bonds. Base pairs are attached to sugar molecules.

Base Pair Classification

Purines: - two fused rings of N, C & H atoms. - Guanine and Adenine. Pyrimidines: - one ring of similar atoms, so a lot smaller than purines. - Cytosine, Thymine & Uracil (in RNA).

RNA Function

RNA carries instructions from DNA in the nucleus to the ribosomes in the cytoplasm of a cell where it controls the synthesis of proteins from amino acids.

RNA Structure

RNA is also a polymer made of nucleotides but differs in structure in that: - RNA is a single strand. - RNA is a shorter strand. - RNAs sugar is ribose. - RNAs bases are the same but Thymine is replaced by Uracil.

Noble Prize

Rosalind Franklin was the only researcher that had q chemistry degree. She suspected that DNA was a helical structure but was reluctant to release information until she had enough proof. She unfortunately died of cancer at 37 years old. In 1962, Watson, Crick and Wilkins won the Noble Prize for the greatest discovery in medicine/physiology but Franklin had already passed away and could therefore not share the prize with the others, because Noble Prizes are only awarded to living people.

How to Base Pairs Link?

Shape and size of bases differ so that: a. A bonds with T or U in RNA by two hydrogen bonds. b. C bonds with G by three hydrogen bonds.

Extra-Cellular DNA

Small amounts of DNA are found outside of the nucleus in the mitochondria (plants and humans) and in the chloroplasts (plants) EXTRANUCLEAR

Mitochondria DNA

Small amounts of DNA are present in the mitochondria. Mitochondrial DNA: a. Is a double-stranded, ring-shaped molecule. b. Comes from the egg cell, and is therefore only inherited from the mother. c. Is shorter than Chromosomal DNA. d. Genes are essential for normal functioning of the mitochondria.

How does DNA Replicate?

The process is catalyzed by the enzyme DNA Polymerase. The double helix unwinds. Weak hydrogen bonds between bases break open to allow to strands to unzip. Each single chain of bases is exposed. Free nucleotides in the cytoplasm become attached to their matching exposed base pairs. Bonding rules ensure that sequence of bases in daughter DNA is identical to mother DNA. Two daughter DNA molecules each twist to form a double helix, which then winds itself around the histones (proteins), forming a chromosome. This process only takes a few seconds.

What is DNA Replication?

The process of making a new DNA molecule, that is identical to the original molecule. This takes place in the nucleus during interphase.

Role of mRNA

The sequence of amino acids is determined by the instructions from genetic code in DNA molecule which is passed onto mRNA molecule. Genetic code is carried as a sequence of "code words" which are transcribed to the mRNA. Each code word is made up of any three bases & is called a codon. There are 64 different codons and all except for 3 code for proteins. Some amino acids are coded for by more than one codon. The three codons that don't code are called stop codons which tell the cell that the process is completed. (UGA, UAA, UAG). Codon is written by using first letter of different bases. Triplet code of bases is the basis of the genetic code as a gene is made up of a group of codons that code for one protein. The order of codons in mRNA will therefore determine the sequence of amino acids which will determine which protein is made.

DNA Makeup

The shape of DNA is rather like a long, twisted ladder. Two strands twist to form a stable, 3D double helix.

Translation of RNA

The start signal begins the process of making a protein. Three codons are stop signals that indicate that a protein is complete. Anticodon bases link up to their complementary bases. Translation - code of mRNA is translated into an amino acid. tRNA molecule is released to carry more amino acids to the ribosome. Catalyzed by enzymes, amino acids link with peptide bonds to form a polypeptide chain. These polypeptide chains link to form a final functional protein.

Extraction of DNA

The technique should: - release as much DNA as possible. - minimize DNA degradation. - be efficient in time, cost, etc.

Role of tRNA

There are 64 different tRNA molecules. These are made from nucleotides and are found in the cytoplasm of the cell. Each tRNA has three bases at one end of molecule called the anticodon, which picks up a specific amino acid found in the cytoplasm & transfers it to a ribosome.

Similarities between DNA & RNA

They both: a. Have polymers; nucleotides with nitrogenous bases, sugar and phosphates; and four nitrogenous bases. b. Are responsible for the synthesis of proteins.

How can Mitochondrial DNA be used?

To reconstruct family maternal-linked relationships. To investigate forensic cases where chromosomal DNA has degraded. To determine if siblings have the same mother.

Transcription of DNA

Transcription is the process by which DNA makes and codes mRNA. Transcription starts when a small piece of DNA unwinds. Process is catalyzed by the enzyme RNA polymerase which causes two strands of DNA to spears by breaking the hydrogen bonds between complimentary bases. Polymerase attaches to and moves along one of the DNA strands causing new nucleotides to pair up with complimentary nucleotides. This DNA sample is called the template. Nucleotides join up, sugar and phosphate are added and new mRNA strand is formed. DNA transcribes genetic code to mRNA. Uracil will pair with Adenine. Completed strand of mRNA breaks from RNA and DNA zips back up. Small mRNA molecule carries code to ribosomes (site of protein synthesis.

Advantages of DNA Profiling

a. Forensics - to identify suspects and victims. b. Diagnosis of inherited disorders - can help parents to make decisions regarding their pregnancy and child. ie - down syndrome. c. Identification of Casualty - army keeps set of DNA from soldiers & can therefore indemnify unrecognized able casualties. d. Fight Illegal Trading - find the origin of timber etc. can be used to track stolen goods.

Disadvantages of DNA Profiling

a. Violation of Privacy - however no identifiable parts are used. b. Issues of Inaccuracy - accuracy depends on the persons experiment, reliability of equipment, etc. c. Manipulation - tampering, irresponsible handling, data manipulation. FALSE INFORMATION.

Protein Synthesis

a. What happens in nucleus? mRNA is formed in the nucleus the same way DNA is replicated. This process is called transcription, as coded message in DNA is carried across (transcribed) into new mRNA molecule which carries it to another molecule. b. What happens in the ribosomes? mRNA binds to ribosome at the start of the codon. Codons of mRNA act as a template that determines the order in which amino acids are linked.