Genetics

Question 1

Nucleotide structure

Answer 1

• A nucleotide is made up of three basic components:
• A pentose sugar made of 5 carbon atoms
• A phosphate group
• A nitrogen containing organic base. These are: Cytosine (C), Thymine (T), Uracil (U), Adenine (A) and Guanine (G).
• They join through condensations reactions just like other molecules releasing water each step up or loosing water each step down

Question 2

Condensation reactions

Answer 2

• Mononucleotide
• A single nucleotide containing the three components
• Dinucleotide
• two nucleotides joined by the sugar and phosphate group to forming
phosphodiester bond
• Polynucleotide
• The linking of mono and dinucleotides to form a long chain single strand
molecule

Question 3

Phosphodiester bond – a C/H reaction

Answer 3

Just like the numbering of the 1’- 4’ glycosidic bond formed between two glucose molecules to form maltose this bond forms between the 3 and 5 numbered carbon atoms on the pentose sugar.
So it is properly known as a the 3’-5’ phosphodiester bond

Question 4

RNA

Answer 4

• A relatively short single stranded polynucleotide chain RNA (ribonucleic acid) containing:
• A molecule of the sugar ribose
• A phosphate group
• A nitrogen containing organic base. These are: Cytosine (C), Uracil (U), Adenine (A) and Guanine (G).
• There are two types of RNA we will cover in the T level:
• mRNA – messenger RNA
• tRNA – transfer RNA

Question 5

Functions of RNA

Answer 5

• RNA transfers genetic information from DNA to the ribosomes where proteins are synthesised. There are two main parts to this process:
• Transcription is the process of copying a segment of DNA into mRNA in the cell’s nucleus.
• Translation is the process in which ribosomes in the cytoplasm or endoplasmic reticulum synthesize proteins after the process of transcription of DNA to mRNA

Question 6

Types of RNA

Answer 6

• mRNA – messenger RNA
• Transcribes (copies) a single strand of DNA in the nucleus to make a copy of the genetic information on DNA and goes to the ribosome.
• tRNA – transfer RNA
• Translates (reads) mRNA in the ribosome to create polypeptides from amino acids and create proteins

Question 7

DNA - 1953 (Francis Crick and James Watson)

Answer 7

• DNA (deoxyribonucleic acid) is a double strand of very long polynucleotides joined together by hydrogen bonds containing:
• A molecule of the sugar deoxyribose (a pentose sugar)
• A phosphate group
• A nitrogen containing organic base. These are:
• Cytosine (C)
• Thymine (T)
• Adenine (A)
• Guanine (G)

Question 8

Base Pairing

Answer 8

• Base pairing in DNA is always specific.
• Adenine always links to Thymine (A-T)
• Guanine always links to Cytosine (G-C)
• They are known as complimentary base pairs
• However…the ratio between A-T and C-G varies from species to species. Humans have a 1.52:1 (AT:CG ratio)

Question 9

Functions of DNA

Answer 9

• DNA is the heredity material responsible for passing genetic information from cell to cell and generation to generation.
• Adaptions allow it to be successful:
• Structural stability reduces opportunities for mutation
• The hydrogen bonds can be broken and repaired during DNA replication
• Huge size means much genetic information can be carried
• The deoxyribose/phosphate skeleton protects the bases from outside chemical and physical forces
• Base pairing allows the replication and transfer of genetic information as mRNA.
• The proportions and sequences of the bases give rise of genetic diversity

Question 10

Coding for Proteins

Answer 10

• M and T RNA work together in protein synthesis which consists of translation of DNA and transcription of RNA into proteins.
• We can use a coding table to show the link between the tRNA and the amino acid chains that are created