DNA Structure and Genetic Codes

Question 1

What is the Role of DNA?

Answer 1

Carries hereditary information from one generation to the next and directs the cell’s activities.

Question 2

Chromosome Role

Answer 2

Carries genetic code for inherited
traits.

Question 3

Genes

Answer 3

Sections of DNA, containing chromosomes, cells, and nuclei.

Question 4

DNA Structure and Location

Answer 4

• Double-stranded helix
• Can self replicate
• Found in cytoplasm in prokaryotes
• Found in nucleus in eukaryotes

Question 5

RNA Structure and Role

Answer 5

• Single-stranded
• Uses genetic code to produce proteins (protein synthesis)
• Joined by hydrogen bonds

Question 6

Nucleotide

Answer 6

Chemical building block of DNA and RNA. Consists of a phosphate, a sugar (deoxyribose or ribose), nitrogenous base.

Question 7

Condensation Polymerisation

Answer 7

Nucleotides join together to make a polynucleotide chain. 5’ to 3’ direction.

Question 8

Pyrimidines

Answer 8

• One ringed
• Cytosine
• Thymine
• Uracil

Question 9

Purines

Answer 9

• Two ringed
• Adenine
• Guanine

Question 10

DNA in Eukaryotic Cells

Answer 10

• Found in nucleus
• Tightly coiled to form chromosomes

Question 11

DNA in Prokaryotic Cells

Answer 11

• Found in nucleoid region
• Large circular chromosomes
• Small circular molecules (plasmids)

Question 12

Messenger RNA (mRNA)

Answer 12

Carries a copy of the DNA’s nucleotide sequence to be translated into proteins.

Question 13

Ribosomal RNA (rRNA)

Answer 13

Forms ribosomes, the site of translation of the mRNA into proteins.

Question 14

Transfer RNA (tRNA)

Answer 14

Carries amino acids to the appropriate positions on the mRNA by matching its anticodon sequence to the complementary sequence in the mRNA.

Question 15

Chromosome Structure (In Eukaryotes)

Answer 15

DNA is tightly coiled around small proteins (histones).

Question 16

Metacentric Chromosomes

Answer 16

Centromere is centrally positioned, giving equal arm lengths.

Question 17

Submetacentric Chromosomes

Answer 17

Centromere towards one end, giving unequal arm lengths (One double the height of the other).

Question 18

Acrocentric Chromosomes

Answer 18

Centromere very close to one end.

Question 19

Telocentric Chromosomes

Answer 19

Centromere at the tip of the arms.

Question 20

Ploidy Level

Answer 20

Number of chromosome sets carried.

Haploid - One set
Diploid - Two sets

Humans have 46 diploids.

Question 21

Homologous Chromosomes

Answer 21

Pairs of chromosomes originating from each parent.

Question 22

Homogametic

Answer 22

Individuals with two similar sex chromosomes.

Question 23

Heterogametic

Answer 23

Individuals with different sex chromosomes.

Question 24

Genome

Answer 24

Complete set of DNA present in an organism, measured in the number of base pairs contained in a haploid set of chromosomes.

Question 25

Allele

Answer 25

One form of a gene.

Question 26

Gene Expression

Answer 26

Process by which the information stored in a gene is used to synthesise a functional gene product (protein or RNA).

Question 27

Transcription Result and Its Steps

Answer 27

- Production of single-stranded mRNA from DNA 1. Initiation - RNA polymerase attaches to the promoter, unwinding and unzipping the DNA molecule by breaking the weak hydrogen bonds between the two strands to expose the bases. 2. Elongation - RNA polymerase "walks" in the 3' to 5' direction. For each nucleotide in the template, RNA polymerase adds a complementary RNA nucleotide to the 3' end of the RNA strand. 3. Termination - The termination site of the gene contains a stop triplet code, which binds release factors that signal termination. RNA polymerase detaches, releasing the mRNA and allowing the DNA molecule to reform.

Question 28

After Transcription, RNA Processing

Answer 28

- The addition of a 5' cap - The addition of a poly-A tail - Splicing (removal) of the introns (mRNA maturation).

Question 29

Translation (Protein Synthesis) Results and Its Steps

Answer 29

Translation is the process in which the codons on mRNA are translated into a sequence of amino acids, resulting in a polypeptide. 1. Initiation - Ribosomal subunit attaches to the 5' end of an mRNA strand. Moves until it reaches a start codon (AUG). - tRNA joins to the mRNA start codon, attaching by complementary base pairing between the codon and anticodon. - Binding of large and small ribosomal subunits causes formation of three special sites for tRNA to bind. - The attachment of amino acids to their corresponding tRNA molecules. 2. Elongation - tRNA with a complementary anticodon to the next codon on the mRNA attaches and adds its specific amino acid. - Continues this. 3. Termination - Attachment of amino acids continues until a stop codon is reached. - Polypeptide chain released from the ribosome into the cytoplasm or the endoplasmic reticulum. - Fully functional polypeptides remain in the cell for use, or are exported for use elsewhere in the organism.

Question 30

Hox Genes

Answer 30

Master regulator that affect the spatial pattern of expression of other genes. Body plan from head to toe.

Question 31

Epigenetics

Answer 31

Altering gene expression without altering the DNA sequence.

Question 32

Mutation

Answer 32

Change in the sequence of nucleotides in DNA.

Question 33

Mutagen

Answer 33

Factors that induce mutations; e.g. radiation (UV)

Question 34

Somatic Mutations

Answer 34

Mutation in any body cell (no sex), and is not inheritable.

Question 35

Germline Mutations

Answer 35

Mutation in gametes (sex cells), and is inheritable.