1-1 DNA Flashcards
what is the definition of DNA
DNA, or deoxyribonucleic acid, is the genetic material found mostly in the nucleus* of a cell, that directs or controls virtually everything that happens in cells.
what is the function of DNA
Stores and transmits genetic information in living things
what does the sequence of nucleotides in DNA determine
the proteins that are produced
what is the structure of DNA
DNA is a large macromolecule made up of repeating units called DNA nucleotides.
The two strands are joined together by ‘weak’ hydrogen bonds
The structure is twisted to form a double helix.
what are the characteristics of eukaryotic cells
In eukaryotes, DNA is arranged in linear chromosomes, which are found in the nucleus.
Well organised cells - much larger in size(10µm-100µm) than prokaryotic cells.
Found in all plants, animals, fungi and protists (mostly single-celled eukaryotic cells).
Has nucleus, containing DNA which is bound to proteins in multiple linear chromosomes.
DNA in eukaryotic cells is also found in the mitochondria and chloroplasts cells.
contains histones
where is DNA found in eukaryotic cells
Most of the DNA is found in linear chromosomes in the nucleus (called the nuclear DNA).
Arranged in linear chromosomes
DNA is also found in mitochondria, called mitochondrial DNA (mtDNA)
DNA is also carried in chloroplasts
definition of a chromosome
An organised structure consisting of a single piece of coiled DNA together with protein, and containing many genes.
what is chromatin
When the cell is not dividing, the chromosomes exist in a form called chromatin (only in eukaryotic cells), which is essentially all the de-condensed chromosomes mixed together (DNA + proteins).
It is important to note that chromosomes only become visible during cell division.
what is a karyotype and what does a human karyotype consist of
the complete collection of all the chromosomes of a particular organism.
A human karyotype consists of 44 autosomes and 2 sex chromosomes.
what are the characteristics of prokaryotic cells
Simple, unspecialised cells.
These cells are very small (1µm-10µm).
Bacteria and cyanobacteria (blue-green algae) are examples of prokaryotic organisms
Almost always exist as unicellular organisms (single cells).
Cytosol is the liquid part of the cytoplasm
Thought to have evolved millions of years before more complex eukaryotic cells.
no histones
where is the DNA found in prokaryotic cells
No nucleus – DNA is located in the nucleoid region of the cytosol in the form of a single circular chromosome.
They may also contain an additional
piece of DNA in the form of a plasmid (a small circular piece of DNA).
what is cell theory
Part of cell theory is that all cells come from pre-existing cells.
DNA is the molecular basis for this.
Before a cell divides, DNA is copied, so that each new cell receives an identical copy.
what is the structure of a nucleotide
Each nucleotide is composed of:
A pentose (5-carbon) sugar called deoxyribose
A phosphate group
One of four nitrogenous bases – adenine(A), cytosine(C), Thymine(T) and guanine(G)
The phosphate is connected to the sugar by a covalent bond, and the sugar in turn is covalently bonded to the nitrogenous base.
what kind of bonds are between the bases and if they are considered weak, how do they hold the helix together
hydrogen bonds between the bases – although ‘weak’ on their own, in their millions, they provide sufficient strength to hold the 2 strands together.
what is dna replication process
- Helicase separates the two strands of DNA and the two strands are separated exposing the DNA bases. (these act as the template for new strands).2. RNA primase adds small piece of DNA (a primer) where the new strand is made.3.DNA polymerase joins free-floating nucleotides to each strand of the original DNA molecule in a complementary manner, in the 5’ to 3’ direction; adenine pairs with thymine, guanine with cytosine. There is a leading and lagging strand.4.
why is it called semi-conservative replication
Each new DNA molecule consists of one ‘old’ or pre-existing strand and one newly synthesised strand – hence semi-conservative replication.
what is the leading and lagging strand of DNA replication
Leading Strand: This is the strand that is synthesized continuously in the same direction as the replication fork (the “unzipping” area where the DNA strands separate). Since DNA polymerase (the enzyme that builds the new DNA) can only work in the 5’ to 3’ direction, the leading strand is replicated smoothly and without interruptions.
Lagging Strand: This strand runs in the opposite direction (3’ to 5’ relative to the replication fork), so it cannot be replicated continuously. Instead, it is synthesized in short, discontinuous segments called Okazaki fragments, which are later joined together by the enzyme DNA ligase. This makes the lagging strand’s process a bit more complex than the leading strand’s.
