The genome Flashcards
What does Adenine bind to?
Thymine
What does Cytosine bind to?
Guanine
What three things make up a nucleotide?
A phosphate, sugar and a base
The sugar phosphate backbone is held together by what type of bonds?
covalent
what type of bonds form between DNA bases?
hydrogen bonds
How many hydrogen bonds forms between Thymine and Adenine?
2
How many hydrogen bonds form between Cytosine and Guanine?
3
What direction is a gene read in?
5 prime to 3 prime
nucleotides are subunits of …….
nucleic acids
How many carbons are in the sugar on a nucleotide?
5
Ribonuncleic acid is single or double stranded?
Single stranded
Why is ribonucleic acid so unstable?
because it is single stranded
Deoxyribose is so stable because….
its double stranded, therefore can form a helix
Pyrimidine is a single of double ring structure?
single
Purine is a single or double ring structure?
double
What 2 bases are pyrimidine compounds?
Thymine and Cytosine
What 2 bases are Purine compounds
Guanine and Adenine
What bonds link nucleotides together?
phosphodiester bonds
What is a phosphodiester bond between in DNA structure?
A 3 carbon on a sugar molecule, and the 5th carbon of another sugar
describe the beads on a string model?
Lines of DNA wound round histones
what is a nucleosome?
a length of DNA coiled around a histone
when would you see DNA in the shape of a mitotic chromosome?
during mitosis (replication and division)
what histones make up a nucleosome?
8 histones (octamer)
x2 H2A, H2B
x3 H3, H4
Are histones positively charged?
yes
Is DNA positively charged?
no
to go from beads on a string to finer structure of DNA what extra histone do you need?
H1
What does H1 do?
allows the DNA to fold back on itself
What two methods allow for DNA replication (Allow access to enzymes)?
- Chromatic remodelling complexes
2. Histone modifying enzymes (add or remove methyl, acetyl or phosphate)
What do histone modifying enzymes do?
They add or remove acetyl, methyl and phosphate
How to histone modifying enzymes work? **
They remove the positive charge on the histone group, so the DNA attached no longer has affinity for it. Histone becomes neutral. DNA then is ‘unpackaged’
Is euchromatin or heterochromatin more coiled?
euchromatin - loosely packed and uncoiled
Is heterochromatin genetically inactive?
yes
Supercoiling of Beta Globin or the HBB gene causes what blood disorder….
severe anaemia
no mutation- gene just folded up a bit too tightly
Supercoiling can affect the way genes are ……..
expressed
Rubinstein-Taybi Syndrome is a ……… disease
chromatin
What are the symptoms of Rubinstein-Taybi
Braod thumbs and broad big toes
retardation
facial abnormalities
how common is Rubinstein-Taybi syndrome
1 in 100,000
what causes Rubinstein-Taybi syndrome?
mutation in histone acetyl-transferase - how they fold
How many pairs of homologous autosomal chromosomes do we have?
22 pairs
and 2 sex chromosomes (46 in total)
Most human cells are diploid or haploid?
diploid (2 copies)
What is a karyotype?
an individuals collection of chromosomes
Down syndrome affects which chromosome?
21, trisomy
