3.1/1.6 Flashcards
what is a gene
a heritable factor that consists of a length of DNA and influences a specific characteristic.
they are lengths of DNA that code to make a protein.
what is a locus (loci)
a position on a chromosome where a gene for a particular trait is located
homologous chromosomes
chromosomes that have the same:
genes,
size,
placement for the centromere
gene loci in the same sequence
pattern of banding
X and Y chromosomes have an unmatched region on the X chromosome as the Y is shorter.
what are alleles
various specific forms of a gene
how much can alleles differ from eachother
one or only a few bases
each allele will show a slight difference in base orders.
this is enough to alter the protein so it is different slightly
homologous pair relationship with alleles
the homologous pair carry alternative forms of a gene which are called alleles
homologous chromosomes carry the same sequence of gene but not necessarily the same alleles of those genes
where are alleles from
one from the mother’s egg
one from the father’s sperm
what are mutations
alterations in the DNA of chromosomes that is not immediately and properly repaired.
what are the 3 typess of mutations
neutral
harmful
benefecial
neutral mutations
neutral or ‘silent’
i.e they have no observable effect on the orgainism
harmful mutations
evident because they may alter the survival capacity of the organism
e.g. sickle cell anemia, cystic fibrosis, albinism
benefecial mutations
benefecial form the basis for evolution. any mutation that improves survival of an organism will of an organism will be passed on
e.g. disease resistance, chlorosterol tolernance, antibiotic resistance in bacteria
causes of mutations
may occur randomly and spontaneously.
may also be induced by enviromental factors
spontaneous mutations
arise from errors in DNA replication.
different genes mute at different rates
induced mutations
can be induced by mutagens
what are mutagens
envriomental factors that cause a change in DNA
examples of mutagens
radiation
viruses
microorganism
enviromental poisons and irritants
alcohol and diet
what do mutations locations determine
whether it will or will not be inherited
most mutations occur in somatic cells and are not inherited
gametic mutations occur in the cells of the gonads( which produce sperm and eggs) and may be inherited
if mutations occur in somatic cell will they be inherited
no
if mutations occur in gametic cell will they be inherited
what are the two types of mutation
gene mutations (change in base sequences)
chromosomes mutations (affects number of chromosomes)
gene mutations
change in base sequences in DNA for a single gene
may produce a new allele of a gene
What is a point mutation
Gene mutations involving a single nucleotide
Playing you DNA sequence may result in what
A new sequence of the amino acids constituting a protein
Because of the degeneracy (corruption) in the genetic code what may happen
Not all changes in any DNA sequence will result in a new sequence of amino acids
Finish the sentence
Even with a change in amino acid sequence…
protein function may be unaffected (the mutation is neutral).
A change THAT FORMS the ‘stop’ codon good what to the polypeptide
It would stop without of the polypeptide at the wrong place
a change IN a ‘stop’ codon would cause what
It would cause the polypeptide to go on and on
Eddie or taking away a nucleotide causes what
A reading frame shift
They continued to read mRNA nucleotides three at a time
Frameshift mutations are usually lethal
Haemoglobin molecules are made up of what
Two alpha (α) chains and two beta (β) chains linked together
What is sicko cell anaemia caused by
An autosomal recessive mutation on chromosome 11
This results in the substitution of a single nucleotide base in the gene encoding for the Beta chain of the haemoglobin in which mutates GAG to GUG which changes the amino acid from glutamic acid to Valine.
This changes the structure of the haemoglobin molecule
Normal red cells containing normal haemoglobin (soluble)
Maximises oxygen-carrying.
sickle cell containing mutant haemoglobin (less soluble) are less efficient at carrying oxygen
The haemoglobin of clusters together to form fibre which deforms the red blood cells into a circle shape
What is a Genome
The whole of the genetic information of an organism
This includes codeine and non-Coding regions
The genome size
The genome size is the total number of DNA base pairs in one copy of other haploid Genome
Comparison of two know the size in T2 phage, Escherichia coli, drsophila melanogastar, homo sapians and Paris japonica
Genome sizes in different haploid genome
Virus T2 phage - 5kb
Escherichia coli (bacteria) 4,600,000kb (4.6 mb) with 4200 genes
drsophila melanogastar (fruitfly) (150 Gb) with 20, 000 genes
Paris japonica 150, 000, 000, 000 (150Gb) (largest plant genome)
Protopterus aetgeopicus 130, 000, 000 (130Gb) (Long fish, largest animal genome)
Eukaryote chromosomes
They usually exist as homologous pairs
are typically two of each kind in the somatic (body) cells of higher plants and animals
The exception to the homologous pairs being the same are the sex chromosomes
Human males have 22 pairs of autosomes (chromosomes other than sex chromosomes) Plus X and Y
Females have 22 pairs of autosomes plus X and X
Chromosomes usually appear as single strands. however, just before cell division the DNA makes a copy of itself (replication)
At this time they have a double-stranded appearance consisting of two sister chromatids connected at the centromere
Eukaryote chromosomes are linear DNA molecules associated with histone proteins
Homologous chromosomes carry the same sequence of genes but not necessarily the same alleles of those genes
In a eukaryotic species, there are different chromosomes that carry different genes
Sex is determined by six chromosomes
Prokaryote chromosome
prokaryotes have one chromosome consisting of a circular DNA molecule
Some prokaryotes also have plasmids but eukaryotes do not
what are autosomes
posture songs are chromosomes that do not determine sex
Diploid nuclei had pairs of what
Homologous chromosomes
what is mitosis
the divison of the nucleus into two genetically identical daughter nuclei
cells follow a pattern follow a pattern for at least part of their lie: growing first, then dividing to produce two new cells
what happens to chro mosomes during mitosis
they condense by supercoiling
cytokinesis occurs…
after mitosis and is different in plant and animal cells
cytokinesis differences in plants and animal cells
animal cells lack a cell whereas plant cells do have a cell wall
in plants a cell plate begins to grow which will become the new cell wall
in animals the ell membranes on opposite sides become pinched which forms a cleavage furrow until the two sides touch
in plants the cell plate extends outwards and fuses with the cell wall, dividing the cell into two distinct daughter cells
Because this separation originates in the centre and moves laterally
how to determine a mitotic index
determines how % cells in a group of cells are undergoing mitosis at a given time
number of cells in mitosis mitotic index = -------------------------------------------- X 100
total number of cells
what is interphase
a very activecell cycle phase with many processes occurring in the nuclear and cytoplasm
how do cells grow
by adding material to their cell
cell divison
cells follow a pattern follow a pattern for at least part of their lie: growing first, then dividing to produce two new cells
cells grow by adding materials to their cell
cells divide by mitosis- a parent cell divides into 2 or more daughter cells
cell division is usually a small segment of a larger cell cycle
cell divison occurs under what 3 circumstances
development and growth
cell replacement
asexual reproduction
development and growth
the no. of cells in an oargainism increases by mitosis
cell replacement
cells in some body areas are constantly gotten rid of and replaced by new cells
the new ones are formed by mitosis and are therefore daughter cells (exact copies) of the replaced cells
asexual reproduction
some organisms reproduce asexually in bacteria and negative reproduction in plants, producing genetically similar offspring
what is interphase
Interphase is an active period in the cell cycle when many metabolic reations occur
Many events need to occur in interphase to prepare the cell for successful division
interphase process
DNA is present as uncondensed chromatin (not visible under microscope)
DNA is contained within a clearly defined nucleus
Centrosomes and other organelles have been duplicated
Cell is enlarged in preparation for division
D-DNA replication – DNA is copied during the S phase of interphase
O-Organelle duplication – Organelles must be duplicated for twin daughter cells
C-Cell growth – Cytoplasmic volume must increase prior to division
T-Transcription / translation – Key proteins and enzymes must be synthesised
O-Obtain nutrients – Vital cellular materials must be present before division
R-Respiration (cellular) – ATP production is needed to drive the division process
Mnemonic: DOCTOR
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interphase - G1
G1 – First intermediate gap stage in which the cell grows and prepares for DNA replication
interphase -S
S – Synthesis stage in which DNA is replicated
interphase - G2
G2 – Second intermediate gap stage in which the cell finishes growing and prepares for cell division
Prophase:
DNA supercoils and chromosomes condense (becoming visible under microscope)
Chromosomes are comprised of genetically identical sister chromatids (joined at a centromere)
Paired centrosomes move to the opposite poles of the cell and form microtubule spindle fibres
The nuclear membrane breaks down and the nucleus dissolves
Metaphase:
Microtubule spindle fibres from both centrosomes connect to the centromere of each chromosome
Microtubule depolymerisation causes spindle fibres to shorten in length and contract
This causes chromosomes to align along the centre of the cell (equatorial plane or metaphase plate)
Anaphase:
Continued contraction of the spindle fibres causes genetically identical sister chromatids to separate
Once the chromatids separate, they are each considered an individual chromosome in their own right
The genetically identical chromosomes move to the opposite poles of the cell
Telophase:
Once the two chromosome sets arrive at the poles, spindle fibres dissolve
Chromosomes decondense (no longer visible under light microscope)
Nuclear membranes reform around each chromosome set
Cytokinesis occurs concurrently, splitting the cell into two
Cytokinesis in animal cells
After anaphase, microtubule filaments form a concentric ring around the centre of the cell
The microfilaments constrict to form a cleavage furrow, which deepens from the periphery towards the centre
When the furrow meets in the centre, the cell becomes completely pinched off and two cells are formed
Because this separation occurs from the outside and moves towards the centre, it is described as centripetal
cytokinesis in plant cells
After anaphase, carbohydrate-rich vesicles form in a row at the centre of the cell (equatorial plane)
The vesicles fuse together and an early cell plate begins to form in the middle of the cell
The cell plate extends outwards and fuses with the cell wall, dividing the cell into two distinct daughter cells
Because this separation originates in the centre and moves laterally, it is described as centrifugal
Haploid nuclei have what
One chromosome of each pair
The number of ———— is a characteristic feature of members of a species
Chromosomes
As humans there are how many pairs of chromosomes in all somatic (body) cells
23 pairs
What is the diploid number
The total number of homologous chromosomes
Is given the symbol number 2n
In humans, 2n=46
What is the haploid number
The number of chromosomes in a single set
Is given the symbol n
This is the number found in the gamates of animals and the spores of plants and is usually equal to half the number of chromosomes found in the body cells of the higher organisms
John cairn’s Technique for measuring the length of DNA molecules
John Cairns (1963) was it the first to determine the length of DNA molecules using a technique called autoradiography
He grew bacterial cells on thymidine; a deoxyribonucleotide made from heavy H^3 hydrogen isotope. The radioactive deoxyribonucleotide was only taken up by the replication DNA. He then reviewed these newly built radioactive strands using autoradiography
what is cancer caused by
gene mutations
cells in the body become abnormal and grow of control as a result of uncontrolled cell divison and growth
how do cancerous cells form
normal cells divide as many times as they needed and then stop.
they attach to other cells and stay in place in tissues
they commit cell suicide when they are no longer needed
cells become cancerous when they lose the ability to stop dividing, to attach to other cells, to stay where they belong and to die at the proper times
the four features of cancerous cells
cells become cancerous when they lose the ability to stop dividing, to attach to other cells, to stay where they belong and to die at the proper times
apoptosis
cell suicude
normal cells commit cell suicide (apoptosis) when they are no longer needed
what is a tumour
a group of cells that has resulted from uncontrolled cell division and growth is called a tumour
