B1.2

• Each long molecule of DNA is called a chromosome
• Most people have 46 chromosomes in each of their cells
• You inherit half your chromosomes from your mom and half from your dad
• Short sections of DNA that code for a characteristic are called genes
• The code that a gene contains causes specific proteins to be made
• The combination of genes in an organism controls how the organism functions and what it looks like
• DNA is made up of two strands joined together by bases
• The two strands of DNA twist together to form a double helix
• DNA is made up of small units called nucleotides
• DNA is a polymer
• Each nucleotide is made up of a sugar, a phosphate group and a base - the two strands are held together by hydrogen bonds between the bases
• The four bases are adenine (A), thymine (T), cytosine (C), guanine (G)
• Base pairs always bond together in the same formation - this is known as complementary base pairing
• Adenine always bonds with thymine
• Guanine always bonds to cytosine
• To leave the nucleus, a copy of the DNA is made called mRNA (messenger RNA)
• mRNA is produced in a process called transcription
• DNA around a gene unzips so that both strands are seperated
• Complementary bases attach to the strand being copied
• There is no thymine in mRNA so a base called uracil (U) binds with adenine
• When complete, the strand of mRNA detaches itself from the nucleus template and the DNA zips back up
• mRNA is small enough to move out of the nucleus
• mRNA travels to subcellular structures called ribosomes in the cytoplasm
• The protein is made in the cytoplasm
• Proteins are made from amino acids
• Different amino acids join together to form different proteins
• The order of nucleotides in DNA determines the type and order of amino acids and this determines which proteins will be produced
• Proteins are made by a process called translation
• During translation, the mRNA attaches to a ribosome
• The ribosome reads the nucleotides on the mRNA in groups of three - these groups are called codons, each triplet codes for a specific amino acid
• The ribosome continues the triplet code adding more amino acids
• The amino acids join together in a chain - this is a protein
• The sequence of amino acids determines how the proteins will fold
• Many types of protein are produced including enzymes and hormones
• DNA -> transcription -> mRNA -> translation -> protein
• Enzymes are biological catalysts that speed up chemical reactions
• Enzymes can build larger molecules from smaller ones and break down larger molecules into smaller ones
• Enzymes, like all proteins, are made up of a long chain of amino acids
• The active site is the part of the enzyme that binds to the substrate
• The molecule that binds to the enzyme is called a substrate