Genetics - Basic Information Flashcards
What is DNA?
It consists of two strands of nucleotide monomers that wrap around one another to form a double helix
What is a nucleotide monomer made up of?
A sugar
A base
A phosphate group
What are the four DNA bases?
Adenine
Cytosine
Guanine
Thymine
What is found in the centre of the DNA double helix?
Bases
What makes up the backbone of the DNA double helix?
Sugars
Phosphates
What directions do the polynucleotide chains run in relation to each other?
They run anti-parallel to one another, as one runs 5’ to 3’ and the other runs from 3’ to 5’
What are the two DNA grooves?
Major groove
Minor groove
What is the major DNA groove?
It occurs where the backbones are far apart
What is the minor DNA groove?
It occurs when the backbones are close together
How are the two polynucleotide chains linked together?
Complementary base-pairing
What are the two DNA base pairings?
Adenine - Thymine
Cytosine - Guanine
What bonds bind DNA bases together?
Hydrogen bonds
Where is DNA located in cells?
Nucleus
Ribsosomes - they contain their own DNA
How is DNA stored in the nucleus?
Chromsomes
Chromatins
What structure is found in the centres of the nucleus?
Nucleolus
What structure is located around the nucleus?
Nuclear envelope
What is the function of the nuclear envelope?
It consists of nuclear pores, which allows the passage of molecules into and out of the nucleus
What are chromosomes?
A single piece of DNA containing many genes, regulatory elements and other nucleotide sequences
What structure divides chromosomes into two sections?
Centromere
What are the two sections of a chromosome? Which section is smaller and which is larger?
P - smaller
Q - larger
What structure is contained within the centromere?
Kinetochore
What is kinetochore?
A protein complex that binds to microtubules
What is the function of kinetochore?
It is involved in cell division
Describe the process in which DNA is packaged into chromosomes
DNA is wrapped around histone proteins to form structures known as nucleosomes
These nucleosomes then fold up to form a chromatin fibre
These fibres then wrap around one another to form a chromosome
Why is DNA wrapped around histone proteins?
DNA is negatively charged
Histone proteins are positively charged
This neutralises the negatively charged DNA, which means that DNA takes up less space and inactive DNA can be folded into inaccessible locations
What are the two types of chromatin?
Heterochromatin
Euchromatin
What is heterochromatin?
It is highly condensed form of chromatin that contains silenced genes
What is euchromatin?
It is an extended form of chromatin that contains active genes
When are chromatins formed?
During the S phase of interphase
What are telomeres?
They are the caps at the end of the DNA strands that protect our chromosomes
They they are repetitive sequences of DNA that code for no particular genes
How do telomeres protect our chromosomes?
They prevent important genes from being deleted during cell division and DNA replication
Describe the end problem of linear DNA replication
After DNA replication, each new DNA strand is shorter at its 5’ end than at the parental DNA’s strand’s 5’ end
This produces a 3’ overhang at one end of each daughter DNA strand
This means that some of our DNA on the 5’ strand is not replicated
This end problem explains why the telomeres are so important in DNA replication, as they are shortened from the DNA, but the important genes aren’t
What is telomerase?
It is an enzyme that fills in the gaps as a result of the end problem of linear DNA replication
Describe how telomerase corrects the end problem of linear DNA replication
It contains a catalytic part and a built-in RNA template.
It binds to the end of a chromosome to add complementary RNA bases to the 3’ end of the DNA strand
Once the 3’ end of the lagging strand template is sufficiently elongated, DNA polymerase adds the complementary nucleotides to the ends of the chromosomes, allowing the ends of the chromosomes to be replicated
DNA is said to be semi-conservative. What does this mean?
This means that one half of each new molecule of DNA is old and the other half is new
Describe the process of DNA replication
The hydrogen bonds hydrogen bonds between the complementary base-pairs are broken by special proteins
This allows the double helix to be unzipped
The new nucleotide molecules then pair with the bases on the two DNA strands
These nucleotides molecules are joined together through the enzyme DNA polymerase.
This enzyme can only add new nucleotides to the 3’ end of the growing strand, as DNA is replicated in the 5’ to 3’ direction
On the lagging strand, DNA polymerase joins the nucleotides into fragments, not a whole strand
This means that this strand requires an additional enzyme, known as ligase, to come and join the fragments together to form one continuous strand
What are exons?
They are the coding regions of DNA
What is the function of exons?
They exit the nucleus in the form of mRNA to be coded into proteins at the ribosome
What are introns?
They are the non-coding regions of DNA
What are introns?
They are the non-coding regions of DNA
What is the function of introns?
They stay inside the nucleus as they don’t need to be coded into proteins at the ribosome
What is a codon?
A set of three bases
What does each codon code for?
One amino acid
OR
STOP/START code
What is degeneracy of the genetic code?
This means that amino acids can be coded by more than one codon
Which two amino acids are not degenerate?
Methionine
Tryptophan
What term is used to refer to codons which refer to the same amino acid?
Synonyms
Where do variations between synonyms occur? What is this called?
Third base of the codon
Wobble position
Why is degeneracy of the genetic code important?
This minimises the effect of genetic mutations, as alterations to the base sequences are less likely to alter the protein being coded for
What amino acid is termed as the START codon?
Methionine
What is the function of the START codon?
This this is the signal for protein synthesis to begin
Why do not all polypeptides begin with methionine?
It can be removed at a later stage
What are the three types of RNA?
mRNA (messenger RNA)
tRNA (transfer RNA)
rRNA (ribosomal RNA)
What is the function of mRNA?
It is involved in transporting the genetic code from the nucleus to the ribosome so that protein synthesis can occur
What is mRNA transcribed from?
DNA
What is the function of tRNA?
It is involved in linking codons to their specific amino acid at the ribosome
What does tRNA consist of?
Anticodons
What is the function of anticodons?
They are able to pair to the codons on the mRNA chain
When this pairing occurs, the amino acid held by the tRNA molecule is joined onto the growing chain of amino acids
What is rRNA?
A component of ribosomes
Where is rRNA produced?
Nucleus
Where is rRNA transported to?
Cytoplasm
What does rRNA combine with to form a ribosome?
Proteins
What is alternative splicing?
It is a process by which the exons of the RNA are reconnected in multiple ways during RNA splicing
The resulting different mRNAs may be translated into different protein isoforms; thus, a single gene may code for multiple proteins
What is the number of chromosomes, autosome pairs and sex chromosome pars in a normal human cell?
Chromosomes - 46
Autosome pairs - 22
Sex chromosome pairs - 1
