lecture 1 Flashcards
What is molecular genetics
- study of structure and function of chromosomes and genes at molecular level
- studies inheritance
- gives info about the genetic variation
Human Genome
- 3.2 billion base pairs
- 3.000 km long
DNA
- carrier of genetic info
- stores encoded messages that regulate and control metabolism and growth -> protein synthesis
- passed on to successive generations (inheritance)
- mutations
- evolution
DNA composition - primary structure
- polymer of nucleotides
- nucleotide = phosphate, deoxyribose and nitrogen base (pyrimidin or purine)
- backbone of phosphate and deoxyribose, linked by 3’-5’ phosphodiester bond
- 5’end : free phosphate (PO4) - beginning of chain
- 3’end: free sugar (OH) - end of chain
- 5’-3’ direction
DNA- secondary structure
- chains are antiparallel -> right-handed double helix (turns clockwise)
- back bone outside (hydrophillic), bases inside (hydrophobic)
- 2 h bonds between A & T, 3 bonds between C & G -> complementary base pairing between purine and pyrimidin
Structure of chromosomes
- DNA concentrated in thread-like structure in the nucleus
- only metaphase chromosomes are visible under the microscope
- vary from 50 mio bp to 250 mio bp
- one chromosome = one linear, continuous DNA double helix
- nucleosome = DNA + octameric histone core
-> beads connected via linker DNA - nucleosome is the DNA condensing unit
- chromatin fiber = flexible, long tubular nucleosomes
-> folded into loops (condensed) -> helical
-> chromatin is the main form of DNA storage (enables replication and transcription of genes)
- chromosome = helical structure of chromatin, further condensed
DNA levels of organisation
-> only macromolecule that can transform its levels of organisation continuously!
DNA - nucleosome - chromatin - chromatin loops - condensed chromatin loops - chromosome
mitochondrial chromosome
- small circular DNA molecule
- 16 kb
- encodes 13 structural genes and some structural RNA genes
- mainly related to maternal type inheritance
DNA Replication: Interphase
- largest part of cell’s life
- cell is preparing for cell division
- strong metabolic activity
- chromosomes are replicated, but not yet distinct ( chromatin fibres)
G1:
- increase in cell size
- duplication of organelles, protein-RNA
- preparation for DNA replication
S:
- DNA replication
G2:
- preparation for cell division
M: mitotic division
Replication Checkpoints
G1 checkpoint
- cell size, nutrients, growth factors, DNA damage
G2 checkpoint
- cell size, DNA replication
M checkpoint
- chromosome attachment to spindle
Crossing over
- prophase 1
- material exchanged between the non-sister chromatids
- generated chromosomes on which genes exist from both parents
- 2-3 events per pair of homologous chromosomes
- contributes to diversity and genetic variations ( also random distribution of chromosomes)
- at chiasmata
Central dogma
DNA - RNA - protein
- RNA is the molecular link
- RNA: ribose, uracil, monoclonal strand
- DNA: deoxyribose, thymine, double-stranded
- Transcription determines
– expression of which genes
– which tissues or cells will have the expressed genes
– specific time of the genes that will be expressed
DNA
- can be replicated
- can be transcribed to RNA
RNA
- can be translated
- can be replicated or reverse transcribed
Proteins
- functional form of genetic information
types of RNA molecules
mRNA
- carries DNA from nucleus to cytoplasm
- encodes amino acid sequence of polypeptide
tRNA
- carries amino acid from cytoplasm to ribosome
rRNA
- combines with proteins to form ribosome
small nuclear RNA
- combines with proteins to form complexes used in eukaryotic RNA processing, eg spliceosomes
2 types of genes
- transcribed to mRNA and translated to polypeptide chains
- transcribed to produce tRNA, snRNA and rRNA, not translated
gene characteristics
- usually discontinuous (exons and introns)
- promoter at 5’UTR
- terminator at 3’UTR
- coding sequence: carries the info, transcribed to RNA
