compendium 11

Question 1

Introduction to DNA

Answer 1

• DNA: deoxyribonucleic acid
• Genetic information contained in nucleus
• Contains genetic information for protein formation/ synthesis
• Approximately 23 000 genes in human genome
• Genes code for proteins
• Only 1.5% of DNA is due to genes
• 98.5% of DNA is non-coding – e.g regulatory sequences, introns, and noncoding DNA – e.g repeat elements - used to call it junk DNA, but is important for regulation gene and protein expression

Question 2

Structure of DNA

Answer 2

 Double-stranded (double helix - twisted ladder)
 Sugar-phosphate backbone
 Complementary nitrogenous bases adenine - thymine
guanine - cytosine
Nitrogenous bases
Cytosine (C) Guanine (G) Adenine (A) Thymine (T)

Question 3

How much DNA is in a cell?

Answer 3

• Each somatic human (body cell, every cell except sperm and egg) cell has two copies of each chromosome – one you inherited from Mum and one from Dad.
• The maternal and paternal chromosomes of a pair are called homologous chromosomes (make a “homologous pair)
• Humans have 22 pairs of autosomal chromosomes and 1 pair of sex chromosomes
– Women have 2 X chromosomes and men have an X and Y
• Somatic cells with 46 chromosomes (23 pairs) are said to be diploid (have
the full amount of DNA)
• Gametes (sperm and egg) only have 1 chromosome of each homologous pair (have 23 chromosomes) and are called haploid (have half the normal amount of DNA)
• When cells are dividing, the chromosomes become easier to see and we can arrange them next to their pair – this kind of map is a karyotype

Question 4

Karyotype

Answer 4

A map of chromosomes in dividing cell, arranged with largest at top and smallest at bottom

Question 5

• Genetics

Answer 5

• study of heredity

Question 6

• Gene

Answer 6

– piece of DNA that codes for a protein

Question 7

• Allele

Answer 7

– alternative form of a gene

Question 8

• Genotype

Answer 8

– the actual gene (allele)

Question 9

• Phenotype

Answer 9

• person’s appearance

Question 10

types of alleles

Answer 10

• Dominant and recessive alleles

Question 11

• Sex-linked traits:

Answer 11

traits affected by genes on sex chromosomes

Question 12

The “proteome”

Answer 12

• Cells are protein factories that constantly synthesize many different
proteins
• These proteins are used for cell functions or can be exported
• The cell’s DNA contains all the instructions the cell needs for making
proteins
• Not all cells make all proteins - some proteins are needed only by
specific cells.
• The “proteome” of a cell is all the proteins that a cell makes, and
“proteomics” is the study of the proteins in a cell.
• The proteome of one cell can be compared to another to see how they
are different.
o a muscle cell vs a skin cell
o a melanoma vs a normal melanocyte

Question 13

Protein synthesis

Answer 13

Transcription
DNA convert to RNA
Translation
RNA convert to protein strand

Question 14

The Central Dogma

Answer 14

Flow of information from DNA to RNA to protein

Question 15

Transcription

Answer 15

• DNA has two strands, but only one
strand of the DNA is used as a
template to make RNA
• Genetic information (a gene) is
copied from a strand of DNA to
make a strand of ribonucleic acid
(RNA) called mRNA (messenger
RNA)
• RNA is like DNA except –
• Sugar: ribose instead of
deoxyribose
• it is single-stranded
• contains uracil instead of
thymine
• RNA acts as an intermediary
between DNA and protein