biology4alevel600

1. DNA and RNA are polynucleotides, made up of long chains of nucleotides. 2. A nucleotide contains a pentose sugar, a phosphate group and a nitrogen-containing base. In RNA the sugar is ribose, and in DNA it is deoxyribose. 3. A DNA molecule consists of two polynucleotide chains, linked by hydrogen bonds between bases. There are four bases – adenine always pairs with thymine, and cytosine with guanine. RNA, which comes in several diff erent forms, has only one polynucleotide chain, although this may be twisted back on itself, as in tRNA. In RNA, the base thymine is replaced by uracil. 4. DNA molecules replicate during interphase by semi-conservative replication. Th e hydrogen bonds between the bases break, allowing free nucleotides to fall into position opposite their complementary ones on each strand of the original DNA molecule. Adjacent nucleotides are then linked, through their phosphates and sugars, to form new strands. Two complete new molecules are thus formed from one old one,...

A gene mutation is a change in the sequence of  nucleotides that may result in an altered polypeptide . A mutation is a random, unpredictable change in the DNA in a cell. It may be: • a change in the sequence of bases in one part of a DNA molecule • an addition of extra DNA to a chromosome or a loss of ONA from it • a change in the total number of chromosomes in a cell. Mutations are most likely to occur during DNA replication, for example when a 'wrong' base may slot into position in the new strand being built. Almost all of these mistakes are immediately repaired by enzymes, but some may persist. Single point mutation.  A change in the sequence of bases in DNA may result in a change in the sequence of amino acids in a protein. (Note that this does not always happen, because there is more than one triplet that codes for each amino acid, so a change in a triplet may not change the amino acid that is coded for.) This in turn may result in a change in the 3-D structure of the...

The genetic code specifies the amino acids that are assembled to make  polypeptides . The way that DNA codes for polypeptides is central to our understanding of how cells and organisms function. A polypeptide is coded for by a gene and that a  gene is a sequence of nucleotides that forms part of a DNA  molecule. The sequence of bases in a DNA molecule is a code that determines the sequence in which amino acids are linked together when making a protein molecule. A sequence of DNA nucleotldes that codes for 1 polypeptide, or for 1protein, is known as a gene . The sequence of amino acids in a protein - its primary structure determines its 3-dimensional shape and therefore its properties and functions. For example, the primary structure of an enzyme determines the shape of its active site, and therefore the substrate with which it can bind. A series of 3 bases in a DNA molecule, called a base triplet, codes for 1 amino acid. The DNA strand that is ...

DNA molecule consists of nucleotides in which the sugar component is deoxyribose whereas the RNA molecule has nucleotides in which the sugar is a ribose . Nucleotides Roles: are monomers for  nucleic acid  polymers, such as  DNA  and  RNA . The genetic material (DNA) is a polymer of 4 different nucleotides. The genetic information is coded in the sequence of nucleotides in a DNA molecule.  adenosine triphosphate (ATP) -  the nucleotide molecule that doesn't include the phosphate group - is energy carrier in metabolic pathways.  are components of some important  coenzymes :  flavin adenine dinucleotide (FAD), nicotinamide adenine dinucleotide phosphate (NADP) and Coenzyme A.  They consist of: A 5-carbon  sugar  (deoxyribose in DNA; ribose in RNA) a phosphate group.  a 1 or 2 ring nitrogen -containing base The bases are usually referred to by their first letters: A = adenin,  G =guamin...