Chapter 9- DNA determines the structure and function of cells Flashcards
define DNA
short for deoxyribonucleic acid, is found in the cells of all organisms and contains genetic information which determines the structure of the cell and the way it functions.
where are most DNA molecules found?
in the nucleus of the cell and are therefore called nuclear DNA.
what is mitochondrial DNA?
this is the small amount of DNA that is found in the mitochondria (mtDNA).
mtDNA makes up less than 1% of the DNA found in humans.
what are the two main types of nucleic acid found in the body?
DNA and RNA.
explain the structure of DNA
DNA is a polymere, a molecule made up of many repeating small units. the small repeating units are called nucleotides.
Each nucleotide is composed of a sugar molecule (deoxyribose in DNA), a phosphate group and a nitrogenous base. There are 4 different nitrogenous bases in DNA; adenine, thymine, guanine and cytosine.
The sugar molecule of one nucleotide bonds to the phosphate group of another, forming a long chain of alternating sugars and phosphates, with side chains of bases.
in DNA how do strands join
by specific bases being attracted to each other by weak hydrogen bonds. the two strands of DNA twist into a spiral shape called double helix.
what determines genetic code?
the order in which nitrogenous bases occur in the DNA molecule.
a code of only 4 letters would not seem to allow many different combinations, but each gene consists of up to 2 million pairs of bases.
how long is a DNA strand in humans?
estimated between 2-3 metres.
what are DNA strands wrapped around?
a group of eight special proteins called histones to form a nucleosome.
define histone
a special protein around which DNA is coiled to form chromatin
explain the difference between chromatin in a non-dividing and dividing cell
in a non-dividing cell, the coiled DNA forms a tangled network called chromatin.
in a dividing cell the coiled chromatin becomes even more tightly coiled, becoming ‘super-coiled’ structures called chromosomes.
how many chromosomes are in a normal human cell?
46
what are chromosomes made up of?
each chromosome is made up of sections of DNA that code for particular protein.
each of these sections is called a gene.
what are some important differences between DNA found in the nucleus and mtDNA?
nuclear DNA is in the form of very long strands that are bound to proteins, the histones.
mtDNA is in the form of small circular molecules that are not bound to proteins.
mtDNA is passed from mother to offspring and nuclear DNA is a combination of both the mother and father.
how many molecules of mtDNA are found in each mitochondrion?
10
explain genes within mtDNA
it has 37 genes, all essential for the function of mitochondrion.
24 of the genes contain the code for making transfer RNA (tRNA) molecules, which are involved in protein synthesis.
the remaining 13 genes contain instructions for making some of the enzymes necessary for the reactions of cellular respiration.
explain DNA replication
the first stage is when the two strands of the DNA molecule are separated by the enzyme helicase. each strand of the separated section contains half he original information. each strand serves as a template for the nucleotides that will form the new strand.
As the base adenine can only pair with thymine and the base cytosine can only pair with guanine, the new strand that forms is identical to the original.
what two enzymes are important in DNA replication?
DNA polymerase - enzyme that joins nucleotides together
DNA ligase - enzyme that joins the short sections of DNA together
what is protein synthesis
the formation of DNA in the cell
instructions for protein synthesis are provided by genetic code
what controls the order of amino acids?
the sequence of bases in DNA controls the order of amino acids, and therefore the type of protein that is produced.
what is RNA?
RNA stands for ribonucleic acid and it is another type of nucleic acid.
like DNA, RNA is composed of a chain of nucleotides.
outline four differences between RNA and DNA
- the sugar molecule is ribose, not deoxyribose. ribose has one more oxygen atom than deoxyribose.
- RNA is single stranded, while DNA is double stranded.
- RNA has bases cytosine, guanine, adenine and uracil. the structures of thymine and uracil are very similar, meaning that uracil is complementary to adenine.
- the RNA strand is able to fold onto itself, forming hydrogen bonds between complementary bases.
what are the different types of RNA?
messenger RNA (mRNA)
Ribosomal RNA (rRNA)
Transfer RNA (tRNA)