Week 2 - Molecular Biology Part 1 (L51)

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DNA, GENE, GENOME and CHROMOSOME

what is genotype?

genetic makeup that determine the phenotype of an individual organism

Homozygous recessive (e.g. bb)

Heterozygous (e.g. Bb)

Homozygous dominant (e.g. BB)

determined by

allele

what is allele?

type

dominant

recessive

different forms of a gene

what is phenotype?

hair colour, skin color, height, glucose level, disease, etc ...

the observable trait

chromosome

structure

centromere

subtelomere

telomere

in human, chromosome is packaged in chromatin

what is chromatin?

a complex consisting of double helix DNA packed with protein histone (nucleosome)

23 paired chromosomes (human)

from 24 chromosomes

human is a diploid organism

what is diploid ?

haploid

only one copy of a chromosome

two copies of a chromosome inherited from each parent

chr17 from mother & father

humans have two versions of a gene e.g. P53

sex chromosome

labelled as chromosome chrX and chrY

Female = Two chrX

Male = chrX + chrY

autosome

chr1 until chr22

What is a genome?

the complete set of genetic material (DNA) in a cell

What is genetic material (DNA)?

can be divided into two, based on location

non-coding region

What is RNA?

can be classed into

non-coding RNA (ncRNA)

does not encode protein

Ribosomal RNA (rRNA) - http://www.bio.miami.edu/dana/250/250SS16_8print.html

merge with other proteins and tRNA to form the ribosome complex

in eukaryotes, a ribosome consist of two subunits

large subunit & small subunit

function of a ribosome is to catalyze the assembly of amino acids into polypeptide chains (i.e. protein)

Transfer RNA (tRNA)

function is to transfer the amino acids from cytoplasm to the ribosome

Antisense RNA

Small interfering RNA (siRNA)

double stranded

coding RNA

encode protein

e.g. Messenger RNA (mRNA)

similar to DNA but

Uracil (U) instead of Thymine (T)

so it has 4 nitrogen bases

Uracil (U)

mostly single-stranded

constitute 97-98%

increasing interest to study this region - very hard

the region that does not involve in encoding protein

classification

non-coding outside gene region

e.g. promoters, repeats, intergenic regions

non-coding inside gene region

e.g. introns

coding region

e.g. BRCA1 gene, TP53 gene, TNF gene

constitute only 2-3%

most studied part of the human genome

the region that code for protein

example of common DNA

Chloroplast DNA

Mitochondrial DNA

Nuclear DNA

DNA = Deoxyribonucleic acid

double-stranded helix

consist of chemical blocks called nucleotides

What is nucleotide?

“bases” vs “nucleotides”

refer to the 4 nitrogenous bases

approximately 3.2 billion base pairs (human)

refers to the entire chemical block, which includes the nitrogen base

4 common nitrogen bases for DNA

Cytosine (C)

Thymine (T)

Guanine (G)

Adenine (A)

consists of a sugar molecule attached to a phosphate group and a nitrogen base

genetic information that gets passed from one generation to the next