Genetic Info Flashcards
Difference in dna and rna
DNA: double stranded, high molecular weight, deoxyribonucleic acid
RNA: single stranded, heterogenous in size, ribonucleic acid, uracil
Difference between ribonucleic and deoxyribonucleic
Ribo has hydroxyl group 2nd carbon
Why is RNA unstable?
Has extra hydroxyl group on 2nd carbon so can be attacked by water
Adv as cels change expression pattern
What is a purine?
A and G
What is T and C
Pyrimidines
Why can several mRNAs be transcribed from some genes
Because exons spliced differently
How many chromosomes
22 autonomies and 1 sex chromosome
How is dna packaged
Packaged into chromatin by histones and other chromosomal proteins
How can chromosomes be identified
By banding pattern
What is upstream and downstream
5’ upstream
3’ downstream
Read in 5’ to 3’ direction
Repeated sequences in dna
50%
Often occur in blocks of tandem repeats
Called satellite DNA
Types of satellite DNA
Minisatellite - highly polymorphic 1000 copies in one block. Found at telomeres.
Microsatellite - smaller. Usually intergenic/ Intronic
Importance of minisatellites at telomeres
-Repeats create heterochromatin at tips which helps protect chromosomes from being digested by nucleuses
-Allows replication of DNA to the tips
Repeats can have negative effects. How?
They can cause mispairing during cell division to give:
• Large scale duplication/deletion between homologous chromosomes
• Translocation of DNA between non-homologous chromosomes
Germline cells?
Cell that divide to generate the gametes
Oocytes (eggs females born with) and spermatogonium
RNA that isnt translated into proteins?
tRNA and rRNA involved in translation of mRNA
But some RNA molecules modify other RNA molecules (snRNA; snoRNA)
microRNA (miRNA)- Bind to 3’UTR of mRNA and inhibit translation
What does detergent treatment of nucleus cause
causes release of decondensed chromatin threads from non-dividing
(interphase cells)
What is the fundamental unit of chromatin?
Nucleosome - DNA wound around a histone core
How are Decondensed chromosomes still structurally organised in non- dividing cells
- Attachment to nuclear skeleton
- has a functional role, for example the clustering of ribosomal
genes in the nucleolus
Heterochromatin
Found at centromeres and telomeres
Highly condensed region of an interphase chromosome
Generally gene poor and transcriptionally inactive
Euchromatin
Prevalent in gene rich areas
less compact allowing access for proteins involved in transcription
Nucleolus
Large structure in the nucleus
Where ribosomal RNA is transcribed and ribosomal subunits are assembled
Two types of chromatin in chromosomes
- Euchromatin
- Heterochromatin
How many histone molecules in a nucleosome made of
8
DNA packaging
- DNA wraps around histones
- Nucleosomes fold up into chromatin
- Fibres compressed further
- Fibres coil up to produce chromatid of a chromosome
Why can protein synthesis not occur during mitosis
because the DNA is so
condensed so enzymes e.g. RNA polymerase can’t access it.
Kinetochores
spindle microtubules attach to the two kinetochores (one for each sister
chromatid) at the centromere
Two types of heterochromatin
- Facultative heterochromatin
In temporarily inactivated (condensed) state - Constitutive heterochromatin
Always inactive and condensed. Preset at centromere and telomeres.
What are dNTPs
Required for replication and repair of dna
They are the building blocks of DNA
they lose two of the phosphate groups when incorporated into DNA during replication via phosphodiester Bond
What are replication origins
Sites where replication can start
Have certain sequences that are recognised
Start codon AUG
Which end can DNA polymerase add nucleotides
3’
What must DNA polymerase require
dNTPs
Template
RNA primer
Okazaki fragment
Synthesised in opposite direction to movement of fork in small fragments
Fragments joined together by DNA ligase
Leading strand
Synthesised in same direction of fork
continuous synthesis
Lagging strand
Lagging strand synthesised discontinuously
In opposite direction to movement of fork
Requires new RNA primers
DNA polymerase adds to new RNA primers to start a new Okazaki fragment
RNA primers removed and replaced with DNA using DNA ligase
What synthesises RNA primers
DNA primase
Role of DNA polymerase
Add nucleotides on 3’ of new strand
Proof read
Replication bubbles ?
Form at multiple origins along length of chromosome
Spread out in both directions until all unite
Efficient and fast replication
Chemical reactions which manage dna
Dpurination - base is lost
Deamination - C to U
UV - adjacent thymines become a dimer
What does Nucleosome consist of
Composed of 8 histones
of 4 types
Roughly 140bp of DNA
DNA positively charged.
No. Negatively charge.
Sugar phosphate backbone is negatively charged
Amino acids positively charged?
Yes
Enzymes that involved in acetylation
Histone acetyl transferases add acetyl
Histone deacetylase remove acetyl
What can be used to track a gene
Microsatellites in non coding regions
Function of micro RNA
To repress synthesis of a protein
Genomic imprinting
Epigenetic change
the process by which only one copy of a gene in an individual (either from their mother or their father) is expressed, while the other copy is suppressed
