Inheritance (DNA Structure and Protein Synthesis)

Question 1

What is the genome of an organism?

Answer 1

The entire set of genetic material in an organism (the entire DNA)

Question 2

What is a gene?

Answer 2

• A small section of DNA within an organism
• Each gene codes for one protein

• These proteins could be structural, like collagen, enzymes, or hormones
• Which proteins are produced affects the characteristics of the organism - we are all slightly different because we all have different genes and therefore produce slightly different proteins

Question 3

Where are genes located?

Answer 3

• On chromosones, which are structures made of DNA (so many genes)
• These chromosones are found within the nucleus of a cell

• In each human cell, there will be 46 (23 pairs) chromosomes, and in gametes there will be just 23 individual chromosones
• In other organisms, the number of chromosomes differ

Question 4

What is the structure of a DNA (deoxyribonucleic acid) molecule?

Answer 4

• Two strands coiled around to form a double helix
• The strands are made of a sugar-phosphate backbone
• The strands are joined together by complimentary nitrogenous bases bonding together through hydrogen bonds
• The base adenine will pair with the base thymine
• The base guanine will pair with the base cytosine

• The process of pairing complimentary bases is essential for processes of cell divison and protein synthesis as each half of the double helix acts as a template to be copied to form a new double helix
• Nucleotide is another name for a base

Question 5

What are triplets of DNA and what do they code for?

Answer 5

• A triplet is 3 contiguous base pairs in a gene (so 6 bases in total)
• Each triplet codes for one amino acid during protein synthesis
• The triplets are non-overlapping, meaning each triplet only codes for one amino acid, and the bases are not shared between triplets (they are independent of eachother)

Question 6

What is the structure of an RNA (ribonucleic acid) molecule?

Answer 6

• Single stranded, so the bases will stick out sideways from the strand
• It contains the base uracil instead of thymine
• Otherwise it is the same as DNA

Question 7

What are the two stages of protein synthesis?

Answer 7

• Transcription
• Translation

Question 8

What is the process of transcription?

Answer 8

• The hydrogen bonds between complimentary base pairs break and the DNA strands will unwind
• The gene necessary to produce the wanted protein which is to be transcribed is therefore exposed
• An mRNA molecule is built by transcribing one of the DNA strands which comprise the gene
• The mRNA molecule will have complimentary bases to that strand (though it will have uracil instead of thymine)
• The mRNA molecule escapes through a pore in the nuclear envelope

A codon is the 3 bases on the mRNA which is complimentary to the triplet on the transcribed DNA strand

Question 9

What is the process of translation?

Answer 9

• After leaving the nucleus, the mRNA molecule will attach to a ribosome in the cytoplasm of the cell
• There will be free tRNA molecules in the cytoplasm, each with an anti-codon complimentary to the codon of an mRNA molecule on one end, and on the other a site where an amino-acid has binded
• The tRNA molecule with a complimentary anti-codon to the codon of an mRNA molecule will bind to the mRNA molecule
• More mRNA molecules will attach to the ribosome in the correct order to form the correct protein, with complimentary tRNA molecules attaching to them
• Two mRNA and tRNA molecules can be attached to the ribosome at one time, and a peptide bond will form between the two amino acids attached to the ends of the tRNA molecule
• In this way, a sequence of amino acids will be formed to make a protein until an mRNA molecule has a stop codon - at this point the process will stop

The amino-acid binded to the tRNA molecule will be specific to its anti-codon