L2 DNA to Genes to Chromosomes Flashcards
what is the basis of heredity?
DNA
What does Chargaff’s rule say?
the content of purines (A and G) is = to the content of pyrimidines (C, U, T)
If the sequence of 1 is known, the other sequence can be predicted…
What is the sense strand?
same as coding strand = anti-template strand = mRNA
the sequence of the ____ is complementary to the gene sequence
probe
5’—TAAGCCAATTGG—3’
3’—ATTCGGTTAACC—5’
flip
5’—CCAATTGGCTTA–3’
in an mRNA - U would replace T!
what three regions make up eukaryotic genes?
coding region - exon
non-coding region - intron
regulatory sequences - promoters, enhancers, silencers
what does the regulatory sequence do?
regulates the rate at which transcription of the gene occurs
what do epigenetic modifications do? - like methylation…
regulate the rate a which transcription occurs
where are genes found?
nucleus and mitochondria
what type of DNA sequence makes up 97-98% of the human genome
extragenic DNA
what are the 3 main types of DNA sequences?
nuclear
extragenic
mitochondrial
how many copies of unique genes are in the nuclear genome?
25,000-30,000
where is the highest gene density of nuclear genes?
subtelomeric region - between centromere and telomere
which regions of nuclear genes are non-coding
- heterochromatic and centromeric regions = transcriptionally inactive
what is the largest nuclear gene?
dystrophin
what is a single copy gene?
unique sequence in the genome that code for one protein - receptors, enzymes, hormones, structural elements of the cell etc.
what is a multigene family and what are the types?
genes with similar functions that have arisen by gene duplication
- classic gene families
- gene superfamilies
what is a classic gene family?
multicopy genes that show a high degree of homology – HOX genes + genes for rRNA, tRNA
what is gene superfamilies?
multicopy genes with similar function but limited gene homology – HLA gene, T-cell receptors
how much of our DNA codes for protein?
less than 2%
what is extragenic DNA and what are the types?
apparently, “junk DNA’ that is not transcriptionally active and has no known function yet…may play a role in gene expression
tandem repeat - based on region and size
- satellite
- minsatellite
- -telomeric
- -hypervariable
- microsatellite
Interspersed
- short interspersed nuclear elements
- long interspersed nuclear elements
how do tandem repeated DNA sequences work?
consist of blocks of tandem repeats of non-coding DNA
what are the types of tandem repeats? what is an important characteristic of them?
VNTR and STR
they are polymorphic and inherited in a co-dominant fashion
what are satellite DNA?
repeated sequences of DNA usually clustered around centromeres of chromosomes
less sense than other DNA sequences
what are telomeric mini satellite?
short (6 nt) repeats found at the end of chromosomes - tellers
added by telomerases after DNA replication and are necessary to prevent the shortening of chromosomes which occurs with age
what is hypervariable minisatellites?
aka VNTR
15-100 nt repeat sequence a number of times
found in/around genes and were previously used for genetic fingerprinting but now STR is used
what are microsatellites?
aka STR
very short (2 nt) ex. CACACACAC but can be 3-4 - repeated 5-50X!
highly variable in repeat number
co-dominant
what repeat extensions are associated with a number of diseases?
trinucleotide repeat expansions
what are SINEs
<500 bp long - make up 10% of human genome
appears to be normal RNAs that were converted to DNA by reverse transcriptase and were reinserted back into the genome
what is the most common SINE in humans
Alu elements
what are LINES?
> 6000 bp long
able to make RNA
code for reverse transcriptase
why might LINEs and SINEs be responsible for many mutations during meiosis?
unequal crossover - there are deletions where exons are maybe..
what are pseudogenes?
sequences that look like real genes but are not functional - no mRNA or protein product..
how were pseudogenes probably made?
evolution
- gene duplication and subsequent mutation
- copying of RNA back to DNA (viral) and reinserted back into genome.
what is mitochondrial DNA?
non-nuclear DNA (similar to prokaryotic gene)
- arisen by endosymbiosis
- single circular DNA - codes for proteins in mito
- maternally inherited in humans - from cytoplasm of oocyte
- mito disorders are only passed through maternal line
- more prone for mutation because the bacterial repair mech. is not as good as eukaryotic mech.
what is DNA wound around and what does that form
histones (proteins)
forms a chromosomes
what is the constricted region of the chromosomes?
centromere
what does the centromere divide the chromosomes into?
2 arms
- p arm = short
- q arm = long
where is DNA most condensed and best visualized - at what stage of mitosis?
metaphase
how many sister chromatids does 1 chromosome have
2
what phase does chromosomes only have 1 chromatid?
interphase - decondensed
microtubules attach to ____ during cell division
centromere kinetochores
what are metacentric chromosomes?
p and q arms are equal in length
example - chromosome 1
what are submetacentric chromosomes?
p arm is shorter than q arm
example - chromosome 4
what are acrocentric chromosomes?
p arm contains little genetic info
example - chromosome 13,14,15,21,22
involved in Robertsonian translocation
codes for rRNA and tRNA
what is karyotyping?
visualizing chromosomes during metaphase - max condensation
how many pairs of autosomes are there?
22 pairs
how many pairs of sex chromosomes?
1 pair
how are chromosomes ordered?
according to size
chromosome 1 is largest
chromosome 21 is smallest
typically where does each chromosome come from?
one from mother and one from father
what is uniparental disomy?
when both the chromosomes of the pair are derived from the same parent
how are karyotypes named?
46, XY male
46, XX female
*normal
how does a Barr body form?
in ALL SOMATIC CELLs in FEMALEs on X chromosome becomes transcriptionally inactive and bundles up
when does x-inactivation (lionization) occur?
early stages of development of female embryos
is X-activation random?
yes, - father x chromosome active in 50% of cells and mother x chromosome active in 50% of cells
like a mosaic
what does it mean when x-activation is fixed?
the same x chromosome is inactivated in all descendants of the cell
what region regulates the x-activation?
x-activation center (Xic) that has teh gene XIST gene
XIST RNA coat one of the x chromosomes = transcriptional interference
what locus is huntington’s disease on?
chromosome 4p
what locus is beta globin on?
chromosome 11
what locus is alpha globin gene on?
chromosome 16
what MIM number does autosomal dominant disorders start with?
1
-marfan syndrome 15..
what MIM number does autosomal recessive disorders start with?
2
-CF 219…
what MIM number does x-linked disorders start with?
3
-Duchenne MD 310..
what MIM number does mitrochondrial disorders start with?
5
- leber hereditary optic neuropathy 535…
