Objective sheet 6 - DNADNA- Deoxyribonucleic acid Found in the cells of all organisms, most DNA molecules are found in the nucleus of each cell. DNA contains the genetic information that determines the structure of the cell and the way it functions. - In the form of long strands - 46 DNA molecules in the nuclei of human cells

Structure of DNA

Name Definition/Function

Histone Proteins which DNA strands coil around, which allows them to fit in the nucleus

Chromatin A tangled network of DNA wrapped around histone proteins

Chromosome A tightly coiled segment of chromatin that forms when a cell is about to divide

Gene Sections of DNA which contain the genetic code which is the stored information that determines the structure and activities of the cell.

DNA Deoxyribonucleic acid, stores the genetic information of the cell

RNA Ribonucleic acid, Transfers genetic code out of the nucleus and translates genetic code into proteins.

Gene Expression The process of copying DNA into mRNA and translating the message into a series of Amino acids (proteins)

Protein Proteins are large molecules consisting of amino acids which our bodies and the cells in our bodies need to function properly.

Protein synthesis The process by which amino acids are linearly arranged into proteins through the involvement of transfer RNA, messenger RNA, and various enzymes.

A DNA molecule is made up of thousands of nucleotides. Each nucleotide consists of deoxyribose sugar, a phosphate group and a nitrogenous base.

The nucleotides bond in a way that they form two chains that are linked at the nitrogenous bases. Bases: Adenine = Thymine Cytosine = Guanine The bond between the pairs is a weak hydrogen bond. The two chains are twisted into a spiral shape known as a double helix.

Replication of DNA When a cell is between cell divisions the DNA molecules undergo replication to form exact replicas of themselves. 1. The enzyme helicase ‘unzips’ the double helix, which breaks apart the hydrogen bond 2. Free nucleotides in the nucleus match up to corresponding bases 3. The enzyme DNA polymerase joins the free nucleotides together forming 2 new

strands 4. DNA Ligase rejoins the hydrogen bonds together

Each chain acs as a template for the nucleotides which will bond to form the new half. As adenine can only pair with thymine and cytosine can only pair with guanine the new half is identical to the original.

Role of DNA in the Cell Provides the instruction for protein synthesis, making proteins in the cell. Synthesis- Combining small molecules to form larger ones.

Role of proteins - Make up the structure of the cell (Cell membrane) - Determine how the cell functions - Enzymes, hormones, antibodies and the structural materials of the cell are all proteins

Role in the body

Structure- Muscles = Actin and Myosin - Hair and Skin = Keratin - Bone and Cartilage = Collagen Transport- Cell membrane = channel and carrier proteins Communication- Hormones - Membrane receptors Metabolism- Enzymes Protection- Antibodies

Eg. > Haemoglobin > Actin and Myosin, in muscles > Fibrin, a protein involved in blood clotting > Collagen, the main components of bones, teeth, cartilage, ligaments and tendons > Insulin > Amylase

Protein structure Organic molecule made of long chains of amino acids 20 amino acids- 9 essential (not made in the body, found in food)

Genetic code The proteins a cell can make are determined by genes, which form parts of the DNA molecules in the nucleus. The order in which the 3 bases occur in a DNA molecule makes up the genetic code.

A sequence of 3 bases is the code for a particular amino acid and is called a triplet.

Transcription

DNA RNA

Double strand helix Single strand or looped clover shape

Bases: Adenine, Guanine, Cytosine, Thymine Bases: Adenine, Guanine, Cytosine, Uracil

Stores genetic information which controls the cells function and structure

Transfers genetic code out of the nucleus and translates genetic code into proteins

Nucleus only Nucleus, Cytoplasm, Ribosomes

Only 1 type mRNA, tRNA

Deoxyribose sugar Ribose sugar

mRNA tRNA

Transcribed from DNA Translates mRNA forming proteins

Simple strand clover shaped loop

Broken down after translation Reactivated with new Amino Acids after translation

Codon Anticodon

Nucleus, Ribosomes, Cytoplasm Cytoplasm

DNA is found in the nucleus, but amino acids are joined together at the ribosomes in the cytosol of the cell. DNA molecules are too large to leave the nucleus, so the code for each AA is taken from the DNA to the ribosomes by Ribonucleic acid (RNA). > Found only as a single strand > Sugar is ribose, not deoxyribose like in DNA

Two types - mRNA, messenger RNA

In transcription the mRNA copies the genetic code from the DNA. Occurs in the Nucleus 1. The two strands of DNA are

‘unzipped’ by the enzyme Helicase 2. The seperate into the coding and

template strands 3. RNA Polymerase causes free RNA

nucleotides to bind together in the complimentary order of the template strand, forming another strand.

4. Once the RNA polymerase reaches a terminator sequence of bases on DNA it stops copying

5. The mRNA separates from the DNA and is identical to the coding strand

6. It leaves the nucleus and the DNA strands rejoin

Eg. DNA template strand sequence = A T G G T C A A DNA coding strand sequence = T A C C A G T T mRNA strand sequence = U A C C A C U U

In DNA every 3 bases = a triplet In mRNA every 3 bases = a codon

Translation- Anabolic process - Takes place in a ribosome

Production of a protein using the information on messenger RNA in a ribosome

- The anticodon determines which amino acid the tRNA carries. - Each tRNA is specific to an Amino Acid

Start codon is always A U G which forms the Amino acid Methionine A peptide bond forms between each amino acid.

After Translation the tRNA goes to collect a new Amino Acid. Translation continues until a stop codon is reached.

ATP is required to form the peptide bonds between the amino acids.

Where is DNA found? In the nucleus and in the mitochondria (mtDNA)

mtDNA is small and circular. There are no proteins present, in every mitochondria there are 5-10 mtDNA. There are 37 genes, 13 of them code for respiratory enzymes, the other 24 code for tRNA.

You only inherit mtDNA from your mother, as the part of the sperm where the mitochondria are found does not enter the egg.

Gene expression and epigenetic The making of proteins from your genetic code. At any moment the body is only producing mRNA for a fraction of your genes. Therefore genes can be switched on or off.

What causes them to be turned on or off? Time of day, the cell, signals from other cells, if the cell is reproducing, the environment.

Epigenetic's “Epi” on top of or in addition to. Changes in gene expression that result from mechanisms other than changes in genes. - Environmental factors - Can be inherited

Identical twins have the same DNA/genes. Epigenetic's helps to control which genes are active in a cell and therefore which proteins are produced.

2 Types 1) Acetylation The addition of an acetyl group to a histone protein

- Turns a gene on, enhances gene expression

2) Methylation A methyl group (CH3) is added to DNA. Added to where there are cytosine and guanine bases. Only to cytosine base, where they are adjacent to the guanine bases - Causes inhibition in gene expression, modifying the coiling chromatin