Chapter 4: The Genetic Code

Question 1

Explain the relationship between cells, nuclei, chromosomes and DNA

Answer 1

• there is a cell
• inside the cell is a nucleus
• inside the nucleus are chromosomes - made up of DNA coiled tightly, each chromosome contains a single DNA molecule, humans have 23 pairs of chromosomes (46 in total) each of which holds DNA that codes for specific genes found in a small section of the chromosome
• DNA is a chemical which carries genetic information in the nuclei of cells - made up of nucleotides made up of phosphate units, sugar units, 4 types of nitrogen bases - double helix shape
• bases are adenine (A), guanine (g), cytosine (c), thymine (t)

Question 2

Describe the relationship between DNA, alleles, genes and chromosomes

Answer 2

• chromosomes are made up of DNA coiled tightly
• DNA is a chemical which carries genetic information in the nuclei of cells - made up of phosphate units, sugar units, 4 types of nitrogen bases - double helix shape
• bases are adenine (A), guanine (g), cytosine (c), thymine (t)
• bases pair up according to complimentary base pairing rule - A to T, C to G - sequence of bases which code for a particular trait are called genes e.g. eyes
• alleles are alternative form of a gene e.g. blue eyes - occurs when there’s slight difference in DNA base sequence

Question 3

Outline the role DNA plays in carrying genes to the next generation and in determining the phenotype

Answer 3

• organisms phenotype are established by their inherited genes
• genes are sections of DNA that codes for a particular characteristic e.g. eyes
• phenotype is the observable trait e.g. blue or brown eyes
• genes can come in alternative forms called alleles which are transmitted to offspring from parents though sexual reproduction
• diploid organisms inherit two alleles for each gene; one from each parent
• if organisms inherits two same alleles for trait then it’s homozygous, if two different alleles then heterozygous
• combination of two alleles for trait is called genotype
• traits can be dominant or recessive - dominant allele will always be expressed in the phenotype if at least one and hides recessive, recessive allele only shows up when 2 are present

Question 4

Use the complimentary base pairing rule to help explain the process of DNA replication

Answer 4

• DNA replication is to ensure every new cells has its own copy of the genetic code, must be replicated before a cell divides
• step 1: an enzyme unwinds the parent DNA strand by breaking the hydrogen bonds between bases - exposes the base pairs
• step 2: new nucleotides are brought in - they bond with bases on the parent DNA molecule according to the complimentary base pairing rule
• complimentary base pairing rule is used to describe how adenine always bonds with thymine (A-T) and cytosine with guanine (C-G)
• step 3: enzymes bond the nucleotides together to form new strand
• step 4: at the end of the process, two new molecules of DNA are produced. Both are exact copies of the original molecule - each winds up forming a helix
• called semi conservative replication because one half of the DNA molecule is an intact strand from the old DNA

Question 5

Explain that DNA contains the genetic code for making proteins and proteins are the building blocks for most of your body

Answer 5

• DNA contains the genetic code for proteins
• proteins in the form of enzymes do most of the work in our bodies like help break down food to release energy and they help to transport chemicals between cells
• the bases that make a gene are arranged in groups of three called a triplet, each triplet carries code for a specific amino acid, a protein is a long chain of amino acids that comes into a specific shape