DNA.docx

[Heredity and Gene Expression] \*\*Know definitions and an example of each\*\* Heredity is the passing on of characteristics from one generation to the next by genes. For example, brown eyed parents tend to have brown eyed children. A gene is a length of DNA on a chromosome that codes for a protei...

[Heredity and Gene Expression] \*\*Know definitions and an example of each\*\* Heredity is the passing on of characteristics from one generation to the next by genes. For example, brown eyed parents tend to have brown eyed children. A gene is a length of DNA on a chromosome that codes for a protein or controls the development of a characteristic. Genes control traits and characteristics. Gene expression is the process by which the information from a gene is used to produce a feature or a protein. For example, if a person has the gene for brown eyes, they will have brown eyes even if they also have the gene for blue eyes, because brown is dominant to blue. [Chromosome structure] Each gene has its own specific position on a chromosome called the locus. Most genes have two different options, called alleles. Alleles are either dominant or recessive. A chromosome is composed of two strands called chromatids held together by a structure called the centromere. When chromosomes are spread out, they are called chromatin. Chromatin consists of DNA and proteins. Before division, cells become shorter and thicker as the DNA coils around histones. When chromosomes replicate, they are called chromatids and are held together by a centromere. (1) A chromosome is an organised length of deoxyribonucleic acid (DNA) and proteins called histones. [Structure of Deoxyribonucleic Acid (DNA)] \- James Watson and Francis Crick discovered the molecular structure of DNA in 1951.\ - DNA is a polymer with thousands of repeating units\ - Basic shape is a double helix\ - Sides of the ladder consist of alternating deoxyribose sugar and phosphate groups. - - The rungs consist of complementary bases held together by hydrogen bonds\ - Fours bases are: Adenine (A), Thymine (T), Guanine (G), and Cytosine (C)\ - Adenine only pairs with Thymine\ - Guanine only pairs with cytosine (2) [Nucleotides]  (3) [DNA Replication] \- DNA replication occurs in the nucleus during interphase of mitosis and meiosis\ - Energy (ATP) and the enzyme DNA polymerase are needed for DNA replication *Process*\ - The double helix opens - it untwists and unzips (hydrogen bonds broken by enzymes) prior to replication\ - Free nucleotides enter nucleus from cytoplasm\ - New nucleotides form a new chain. Each strand acts as a template to make the opposite strand from complementary nucleotides.\ - Each new DNA molecule is (i) half new and half old, (ii) identical to the original and each other\ - Each new piece of DNA rewinds to form a double helix\ - Identical helices are formed i.e., the original DNA molecule makes 2 exact replicas of itself Replication of DNA is necessary to pass on genetic code/information exactly from generation to generation. [Structure of Ribonucleic Acid (RNA)] Differences between RNA and DNA\ - RNA contains the sugar ribose instead of deoxyribose\ - The base thymine found in DNA is replaced by uracil in RNA\ - RNA is single stranded while DNA is double stranded (4)\ There are three different types of RNA: \*\*need to know mRNA\*\*\ - Messenger RNA (mRNA): Carries the information from the DNA in the nucleus to the ribosomes in the cytoplasm, where the ribosomes use the information to produce proteins\ - Ribosomal RNA (rRNA): Major part of the structure of ribosomes. Produced in the nucleolus and assembled in the cytoplasm\ - Transfer RNA (tRNA) -- Collects and brings specific amino acids found in the cytoplasm to the ribosomes to be assembled into proteins [DNA profiling] DNA profiling is a method of making a unique pattern of bands from the DNA of a person, which is used to distinguish that DNA from other DNA. *Process\ *- DNA is extracted from cells e.g., blood or semen by breaking up the cell membrane. *\ -* DNA amplification can be used if the quantity of DNA is low. Increasing the quantity is done by a technique called the polymerase chain reaction (PCR)*\ -* Restriction enzymes are used to cut the DNA wherever a specific base sequence occurs (mostly junk genes which are highly variable). This base sequence occurs at a different set of positions in everyone. The sets vary in size (length) and number*\ -* Gel electrophoresis - the fragments are separated, using an electric current, along a piece of gel. The smaller the fragment the faster they travel along the gel*\ -* The DNA is then transferred onto a nylon membrane for ease of use. The fragments are made visible by attaching radioactive pieces of DNA to them that produce a bar-code-like design on an X-ray film *Uses*\ DNA profiles can be used to identify criminals from crime scenes or fathers in paternity cases\ (5) [Genetic Screening] \*\*Process not required\*\* Genetic screening is checking for the presence or absence of a particular allele or gene. A length of DNA with the same base sequence as that of a particular allele labelled either with a radioactive or fluorescent marker is added to a sample of a person's DNA. If the marker sticks to the DNA, it shows that the gene is present. This can be used to check for the presence of genes for cystic fibrosis or hemochromatosis, which are two inheritable diseases common in Ireland.