Genetic information, variation and relationships between organisms 4 Flashcards
What is a ribosome made up of
Ribosomal RNA and ribosomal proteins
what is genome
the complete set of genes in a cell
What is a proteome
the full range of proteins that a cell can produce
Compare and contrast the DNA in eukaryotic cells with the DNA in prokaryotic cells (5)
nucleotides are all joined by phosphodiester bonds
Nucleotide structure is identical
ED is longer
ED is linear, PD is circular
ED is associated with histones, PD is not
Haemoglobins are chemically similar molecules found in many different species.
Differences in the primary structure of haemoglobin molecules can provide evidence of phylogenetic (evolutionary) relationships between species.
Explain how. (5)
Mutations change the base sequence
So a change occurs in the amino acid sequence
Mutations build up over time
More mutations mean more differences between distantly related species
so more distantly related specie have a earlier common ancestor
When preparing the cells for observation the scientist placed them in a solution that
had a slightly higher (less negative) water potential than the cytoplasm. This did not
cause the cells to burst but moved the chromosomes further apart in order to reduce
the overlapping of the chromosomes when observed with an optical microscope.
Suggest how this procedure moved the chromosomes apart.
Water moves into the cells by osmosis
So the cells get bigger
What is a homologous pair of chromosomes?
Two chromosomes that carry the same genes
draw out the structure of an amino acid
compare to notes
what is a gene
a base sequence of DNA that codes for an amino acid sequence of a poly peptide
whats a loci/locus
there place where a gene occupies a fixed position
What are three things about the genetic code that we must know
degenerate
non-overlapping
universal
what does the genetic code being universal mean
the same triplet always codes for the same amino acid in all species
what does the genetic code being degenerate mean
most amino acids are each coded for by more than one triplet
what does the genetic code being non overlapping mean
each base is part of only one triplet; the triplets do not overlap
draw the structure of a DNA nucleotide and label
compare to notes
compare dna nucleotides to rna nucleotides
rna n will contain uracil instead of thymine, dna n will contain thymine instead of uracil
what joins two nucleotides together
phosphodiester bonds
what makes the DNA double helix so stable (2)
the sugar-phosphate backbone protects the organic bases from chemical attack
the hydrogen bonds between the many pairs of complementary bases hold the two strands together; hydrogen bonds are weak on their own, but in mass are relatively strong
compare rna to dna (4)
sugar -deoxyribose vs ribose
bases - thymine vs uracil
strands - double stranded vs single stranded
length - longer vs shorter
outline transcription
Hydrogen bonds between DNA bases break
Only one DNA strand acts as a template;
Free RNA nucleotides align by complementary base pairing;
In RNA, uracil is used in place of thymine;
RNA polymerase is the enzyme that joins adjacent RNA nucleotides via phosphodiester bonds;
Pre-mRNA is spliced (introns removed) to form mRNA (a process called “splicing”).
outline translation
mRNA attaches to ribosome;
The ribosome finds the start codon;
tRNA anticodons bind to complementary mRNA codons;
tRNA brings a specific amino acid;
Ribosome can hold two tRNAs at any one time;
Amino acids join by peptide bonds via a condensation reaction;
Joining of amino acids with peptide bonds requires energy released from the hydrolysis of ATP;
tRNA released after an amino acid joined to polypeptide;
The ribosome moves along the mRNA, codon by codon, to form the polypeptide;
what is a codon
base triplet on mRNA
what is an anticodon
base triplet on tRNA
what is the codon that marks where the ribosome will start translation
AUG
What is the role of RNA polymerase in transcription
to join adjacent nucleotides using phosphodiester bonds to form a strand of mRNA
name the organelle involved in translation
rough endoplasmic reticulum / ribosome
what shape is tRNA
cloverleaf
what is needed to attach an amino acid to tRNA
energy from hydrolysis of ATP
structural differences between mRNA and tRNA
mRNA does not have hydrogen bonds within itself, tRNA does, hence the cloverleaf shape
mRNA does not have an amino acid binding site, tRNA does
mRNA has more nucleotides than tRNA does in its structure
different mRNAs will have different lengths; all tRNAs are similar length
mRNA has codons, tRNA has an anticodon
what leads to tRNA being the shape it is
hydrogen bonds between complementary base pairs within the tRNA strand pulling the structure together
explain what would happen if a mutation were to occur to the gene that codes for the tRNA molecule
a change in the DNA base sequence, so a different nucleotide strand is synthesised
There will be a different arrangement of where hydrogen bonds an form along the nucleotide chain, so the cloverleaf shape may not take place, and there may not be the amino acid binding site shape
meaning the amino acid is no longer complementary to the tRNA
so the tRNA is essentially inactive
differences in protein synthesis between prokaryotes and eukaryotes
E have introns, P do not
in E, transcription occurs in the nucleus. In P, transcription occurs in the cytoplasm or rough ER
E use larger ribosome in the cytoplasm, P use smaller ribosomes
why are some gene mutations disadvantageous
some mutations result in a change in a polypeptide that leads to harmful change in the properties of the protein
this then decreases the chance of the organisms surviving to reproduce
why are some gene mutations disadvantageous
the change in the polypeptide leads to beneficial change in the properties of the protein
this then increases the chance of the organisms survive to reproduce
why are addition and deletion mutations the most harmful (3)
they cause frameshift mutations, where all base triplets are moved downstream from the mutation, so more than one amino acid is affected
define the term exon
base sequence that codes for a polypeptide of amino acids
Not all mutations in the nucleotide sequence of a gene cause a change in the structure of a polypeptide. Give two reasons why
triplets can code for the same amino acid as the DNA base sequence is degenerate
the mutation may occur in the introns, and so is spliced out
what is the name given to any factor that can increase the rate of mutations
mutagenic agent
what are some examples of mutagenic agents
UV light, smoking, poor diet, drugs, chemicals like benzene
in what part of the cell cycle does DNA replication occur in
interphase (S for synthesis)
what occurs in prophase
chromosomes condense and become visible
the nucleosome disappears and the nuclear envelope breaks down
chromosomes appear as two sister chromatids joined at the centromere
spindle fibres extend to poles of the cell
what occurs in metaphase
chromosomes line up on the equator of the cell, and they become attached to spindle fibres by their centromeres
what occurs in anaphase
the cnetromere splits and the chromosomes are pulled to opposite poles of the cell by the shortening of spindle fibres
what happens in telophase
chromosomes decondense into chromatin, the nuclear envelope reforms and the nucleosome becomes visible again
what are the 4 importances of mitosis
increase in cell number to allow growth of the organism
replaces cells to allow repair of tissues
produces genetically identical cells
can sometimes allow asexual reproduction
what happens in binary fission of prokaryotic cells
replication of circular DNA and of plasmids
the cytoplasm divides to produce two daughter cells, each with a single copy of circular DNA and variable copies of plasmids
does meiosis occur is prokaryotes
no
what does meiosis produce
two daughter cells that are genetically different from each other
meaning of diploid
two complete sets of chromosomes, one from each parent
meaning of haploid
having a single set of unpaired chromosomes
what is independent segregation
the random order of which the maternal and paternal chromosomes line up on the equator in the metaphase I step of meiosis
equation for the gamete combinations possible with independent segregation
2 ^x
where x is the number of pairs of chromosomes
what increases genetic variation other than meiosis
random fusion of gametes; which sperm will fertilise which egg
which member of the species will mate with another random member of that species
meaning of diploid
contains two complete sets of chromosomes, one maternal and one paternal
meaning of haploid
having a single set of chromosomes
what is non-disjunction
the failure of homologous chromosomes or sister chromatids to separate properly, caused by spindle failure
