A2. Genes and Chromosomes

Question 1

Genes

DNA contains genes. A gene is … The ____________of ______ _____in a _______________forms the primary structure of a protein

Different polypeptides have a different number and order of amino acids. It’s the order of ______in a _____that determines the order of amino acids in a particular polypeptide.
Each amino acid is coded for by a _______________of ______ ______in a gene called a ________or ______. To make a polypeptide, DNA is first copied into ______________ ____(mRNA). This is the first stage of protein synthesis.
Genes that don’t code for a polypeptide code for functional ____instead. Functional RNA is RNA molecules other than mRNA, which perform special tasks during protein synthesis, e.g. tRNA and ribosomal RNA (rRNA), which forms part of ribosomes.
The complete set of genes in a cell is known as the cell’s __________and the full range of proteins that the cell is able to produce is known as the ___________.

Answer 1

DNA contains genes. A gene is a sequence of DNA bases that codes for either a polypeptide or functional RNA. The sequence of amino acids in a polypeptide forms the primary structure of a protein

Different polypeptides have a different number and order of amino acids. It’s the order of bases in a gene that determines the order of amino acids in a particular polypeptide.
Each amino acid is coded for by a sequence of three bases in a gene called a triplet or codon. To make a polypeptide, DNA is first copied into messenger RNA (mRNA). This is the first stage of protein synthesis.
Genes that don’t code for a polypeptide code for functional RNA instead. Functional RNA is RNA molecules other than mRNA, which perform special tasks during protein synthesis, e.g. tRNA and ribosomal RNA (rRNA), which forms part of ribosomes.
The complete set of genes in a cell is known as the cell’s genome and the full range of proteins that the cell is able to produce is known as the proteome.

Question 2

Non-coding DNA

In eukaryotes, a lot of the nuclear DNA (DNA stored in the nucleus) doesn’t code for polypeptides. Some genes don’t code for polypeptides at all—they code for functional ____
Even genes that do code for polypeptides contain sections that don’t code for amino acids. These sections of DNA are called ______. There can be several introns within a gene and their purpose isn’t known for sure. Introns in ____________are removed during protein synthesis - so they don’t affect the amino acid order. _____________ DNA doesn’t have introns. All the bits of a gene that do code for amino acids are called exons.
Eukaryotic DNA also contains regions of ________ ________. These areas don’t code for amino acids either, so they’re called …

Answer 2

Non-coding DNA
In eukaryotes, a lot of the nuclear DNA (DNA stored in the nucleus) doesn’t code for polypeptides. Some genes don’t code for polypeptides at all—they code for functional RNA
Even genes that do code for polypeptides contain sections that don’t code for amino acids. These sections of DNA are called introns. There can be several introns within a gene and their purpose isn’t known for sure. Introns in eukaryotes are removed during protein synthesis - so they don’t affect the amino acid order. Prokaryotic DNA doesn’t have introns. All the bits of a gene that do code for amino acids are called exons.
Eukaryotic DNA also contains regions of multiple repeats outside of genes. These are DNA sequences that repeat over and over. For example: CCTTCCTTCCTT. These areas don’t code for amino acids either, so they’re
called non-coding multiple repeats.

Question 3

Alleles
A ____can exist in more than one ___. These forms are called alleles. The order of ______in each allele is slightly different, so they code for slightly ____________versions of the same _____________.

Answer 3

Alleles
A gene can exist in more than one form. These forms are called alleles. The order of bases in each allele is slightly different, so they code for slightly different versions of the same polypeptide.

Question 4

Homologous chromosomes
In a eukaryotic cell nucleus, DNA is stored as chromosomes. Humans have 23 pairs of chromosomes, 46 in total -two number 1s, two number 2s, two number 3s, etc. Pairs of matching chromosomes (e.g. the 1s) are called _____________ _____.

In a homologous pair both chromosomes are the _____ _____and have the same _____, although they could have ___________ ________. Alleles coding for the same characteristic will be found at the same fixed position (______) on each chromosome in a ______________ ____.

Figure 3: Diagram showing a pair of homologous chromosomes.

Answer 4

Homologous chromosomes
In a eukaryotic cell nucleus, DNA is stored as chromosomes. Humans have 23 pairs of chromosomes, 46 in total -two number 1s, two number 2s, two number 3s, etc. Pairs of matching chromosomes (e.g. the 1s) are called homologous pairs.

In a homologous pair both chromosomes are the same size and have the same genes, although they could have different alleles. Alleles coding for the same characteristic will be found at the same fixed position (locus) on each chromosome in a homologous pair.