topic 3 - voice of the genome Flashcards
nucleus
- description
- function
- large, surrounded by double membrane called the nuclear envelope
- contains pores for molecules to enter and leave
- contains DNA wrapped in histone proteins in a complex called chromatin
- nucleolus - site of ribosome synthesis
- controls cells activities by controlling transcription of DNA
- nucleolus makes ribosomes
lysosomes
- description
- function
- round organelle surrounded by single membrane
- no clear internal structure
- contains digestive enzymes used to digest invading cells or to break down old components of cell
ribosome
- description
-function
- floats free in cytoplasm or is attached to RER. made of proteins and RNA.
- site of protein synthesis
RER
- description
- function
- series of flattened sacs enclosed by a membrane with ribosomes on surface
- folds and processes proteins that were made at ribosomes
SER
- description
- function
system of membrane bound sacs
synthesises and processes lipids
golgi apparatus
- description
-function
- fluid filled, flattened sacs with vesicles surrounding edges
- packages and processes new lipids and proteins
- makes lysosomes
mitochondria
- description
-function
- surrounded by double membrane called envelope
- inner membrane folded to form cristae
- fluid matrix inside containing enzymes for respiration
- site of aerobic respuration
- where ATP is produced
centriole
- description
- function
hollow cylinders with ring of microtubules arranged at right angles
involved in separation of chromosomes in cell division
cell wall (PLANTS ONLY)
- description
- function
- surround cell. made up of cellulose
- strengthens and supports cell, contains pores for transport
chloroplast (PLANTS ONLY)
- description
- function
- small flattened structure, contains double membrane.
- inner membrane is stacked into thylakoid
- contains chlorophyll
- site of photosynthesis
amyloplast (PLANTS ONLY)
- description
-function
- small, enclosed by membrane
- synthesis and stores starch molecules and breaks them into gluocse
vacuole (PLANTS ONLY)
- description
- function
surrounded by membrane called a tonoplast (controls what enters and leaves)
- contains cell sap
- keeps cell turgid - stops plants wilting and also breaks down unwanted chemicals
plasmodesmata
- description
-function
channels of cytoplasm between adjacent cell walls
- allow communication and exchange of substances
pits
- description
-function
- sections of cell wall where plants can communicate and exchange substances
- the cell wall only has one layer
middle lamella
- description
- function
- made of pectin
- sticks plant cell walls together
describe stages of protein trafficking
- proteins are made on ribosomes
- proteins produced on ribosomes on surface of RER and folded and processes in RER
- proteins then transported from RER to golgi apparatus in vesicles
- they are modified in golgi apparatus
- gogli packages proteins into vesicles to be transported around cell or leave by exocytosis
plasma membrane
- structure
- function
- mainly made of lipids and proteins
- controls movement of substances into and out of cell
cell wall (prokaryotes)
- structure
- function
- made of peptidoglycan
- supports the cell/ prevents it from changing shape
pili (prokaryotes)
- function
- helps prokaryotes stick to other cells and can be used in transfer of genetic material between cells
slime capsule (prokaryotes)
- function
helps to retain moisture, adhere to surfaces and protect bacteria from attack by cells of the immune system
mesosomes (prokaryotic)
- structure
- function
- inward folds of the plasma membrane
- may play a role in cellular processes or may just be artefacts
plasmids (prokaryotes)
- function
- small loops of DNA that contain genes for processes like antibiotic resistance. not always present
DNA (prokaryotes)
- where is it?
floats free in cytoplasm, not attached to any histone proteins
flagellum
- function
- tail like structure that rotates to help cell move
stem cells definition
stem cells are undifferentiated cells which can CONTINUE dividing to give rise to other cell types
what are the three types of stem cells and explain them.
- multipotent cells: can give rise to many different types of cells
- pluripotent cells: can give rise to many types of specialised cells because genes in pluripotent cells are inactivated and thus cant differentiate into all types
- totipotent cells: can give rise to all specialised cells, including placental cells
what can stem cells treat?
arguments for and against stem cells?
- can treat variety of diseases eg diabetes, MS, parkinsons. can also replace damaged tissue in spinal cord injuries.
- for: could save many lives and improve people’s quality of life
- against: embryos are killed in the process of embryonic stem cell extraction. theres also a risk of infection. cells could become cancerous
how does differential gene expression allow cells to become specialised?
- a stimulus acts on unspecialised cells
- activator and repressor molecules can bind to promoter regions on DNA sequence. some genes are switched on and become active whereas others are switched off (eg by changing the structure of chromatin)
- active genes are transcribed to produce RNA
- mRNA is then translated on ribosomes and produces protein
- the protein has ability to change structure and function of cells
explain the Lac Operon (an eg of epigenetic changes)
- E Coli is a bacteria that respires glucose, but uses lactose when glucose not available
- the genes that produce the enzyme needed to respire lactose are found on the LAC OPERON
- when lactose NOT present : regulatory gene produces the lac repressor (a transcription factor that binds to operator site). this blocks transcription as RNA polymerase cannot bind to the promoter
- when lactose PRESENT: lactose binds to the repressor, changing the repressors shape so it cant bind to the operator site. RNA polymerase can now begin transcription
phenotype definition:
the characteristics of an organism, which result from interaction of the genes of an organism with the environment it lives in
explain the two types of phenotype variation
- continuous: variation within a range eg mass
- discontinuous: can only take particular values eg shoe size
epigenetic modifications definition and two examples
- epigenetic modifications are modifications to DNA which do not change the base sequence, but modify the activation of certain genes
- two egs: DNA methylation and histone modification
explain DNA methylation
the process by which methyl groups are added to DNA.
- causes the histone complex to condense
- methylation modifies the function of the DNA, suppressing gene transcription.
- the change is permanent
explain histone modification
The addition or removal of acetyl groups
1. When histones are acetylated, chromatin is less condensed allowing proteins to bind to DNA so genes can be transcribed
2. When acetyl groups removed, chromatin is highly condensed so genes cannot be transcribed
why is bone marrow used for stem cells
- bone marrow contains unspecialised cells
- these are needed because they have the ability to differentiate into other types of cell
how can stem cells be used to cure a patient
- stem cells are from same patient, thus no rejection
- stem cells receive stimulus from surrounding heart cells
- causes genes to be activated
- active genes transcribed to produce mRNA
- mRNA is translated to produce proteins
Describe how society controls the use of embryonic stem cells in medical
research.
A description that makes reference to the following:
• regulatory bodies / laws / High Court (1)
Plus any three from:
• setting or considering ethical / moral aspects (1)
• judging what is acceptable / follow a code of practice (1)
• checking that source of stem cells is acceptable (1)
• decide on maximum age of embryo allowed for research
/ nervous system develops / feels pain (1)
• human cloning is illegal (1)
Explain how epigenetic changes can cause differences in a characteristic.
histone modification / DNA methylation (1)
• {affects activation of / activates / deactivates} genes (1)
• affecting { enzyme production / metabolism } (1)
What does monogenic mean
Only controlled by one gene: tend to show discontinuous variation
What does polygenic mean
Controlled by a no of genes at different loci - show continuous variation
Continuos variation
No distinct categories eg height
Discontinuous variation
Two or more distinct categories eg blood group
How can epigenetic changes be passed on after cell division
- When a cell divides and replicates, changes to its gene expression may be passed on to resulting daughter cells.
- If passed on, this means certain genes activated/deactivated in original cells will also be in daughter cells
- Daughter cells will be equipped to deal with changed environment like original cell
the wall of the sieve tube element contains?
hemicellulose, microfibrils and pectin
why does a sieve tube not require RER and ribosomes
there will be no transcription
no proteins will be synthesised to be processed in RER
which compounds in plants contain nitrogen from nitrate ions
DNA, enzymes and amino acids
how are nitrate ions transported from root to leaves
- through xylem vessels
- in water/ transpiration stream
Explain the effects of a shortage of magnesium ions on a plant.
- limits production of chlorophyll
- lack of glucose due to less photosynthesis
- plants may be yellow and small
give three examples of aseptic technique
- “flaming” instruments
- keeping lids off for short time
- disinfecting bench
why can bacteria grow rapidly in skin wounds
the temperature is warm, increasing the rate of reactions
in bacteria (1)
availability of energy source from { tissue / blood } (1)
availability of water for bacterial cell functions (1)
consideration of the role of oxygen (1)
State suitable conditions for keeping seeds in a seed bank.
cold
dry
why should starch be broken down before being used by cells of plant
- to produce glucose
- as it is soluble
where is calcium pectate found
middle lamella
what properties does lignin give to cell walls
strength and waterproofing
Explain how the structure and properties of starch are related to its function as a
storage molecule
contains glucose needed for energy
insoluble so no osmotic effect
amylopectin is branched
Give reasons why the use of fibres from plants is sustainable.
more plants can be grown (1)
{plants / plant fibres} are a renewable resource
what variables need to be controlled when testing tensile strength of fibres
- temp and humidity
allele definition
alternative form of a gene found at the same locus
what is the locus of a gene
its location on a chromosome
alleles on the same chromosome are…
- autosomally linked
- the closer the loci of the genes on the chromosome, the more closely linked they are
- this is as they are less likely to be separated during recombination in meiosis
why are some genetic disorders sex-linked and more common in men?
- some genes are sex linked as they occur on the X chromosome
- they’re more common in men as the y chromosome is smaller than the x, so men only need one copy of the allele to be expressed
- Females, having two copies of the X chromosome, are likely to inherit one
dominant allele that masks the effect of the recessive allele
what are the three stages of the cell cycle?
interphase
mitosis
cytokinesis
three stages of interphase
G1 - cell grows
S- chromsomes replicated, begin to condense to form chromatin
G2- the cell prepares to divide, replicating organelles for a full set in each new cell
four stages of mitosis
- prophase: chromsomes condense and become chromatids. spindles form. nuclear envelope breaks down
- metaphase: chromsomes move to equator. spindle fibres attach to centromeres
- Anaphase: spindle fibres shorten, centromeres split, sister chromatids seperate to opposite poles
- telophase: chromsomes unravel. nuclear membrane reforms to make two nuclei
cytokinesis
-the whole cell divides and one nucleus moves into each cell to create two genetically identical daughter cells
ovum structure
zona pellucida: protective coating which the sperm have to penetrate for fertilisation to occur. it hardens once the sperm has entered. prevents polyspermy
haploid nucleus: so that a full set of chromosomes is restored at fertilisation
cortical granules: releases substances that cause the zona pellucida to harden
follicle cells: form protective coating around egg
sperm structure
- contain many mitochondria to provide energy for rotation of flagellum
- acrosomes contain digestive enzymes to break down zona pellucida
describe the process of fertilisation (4 steps)
- sperm head meets the protective jelly layer around the egg cell called the zona pellucida and the acrosome reaction occurs: enzymes digest the zona pelllucids
- the sperm head fuses with the cell membrane of the egg cell allowing the sperm nucleus to enter the egg cell
- cortical reaction occurs which causes the zona pellucida to harden and prevent polyspermy
- nuclei fuse and a full set of chromosomes is restored, forming a diploid zygote
what does meiosis give rise to and what is its main role?
- gives rise to genetic variation
- the production of haploid gametes and maintenance of chromosome number
how is genetic variation achieved in meiosis
crossing over - the exchange of sections of DNA between homologous chromosomes
independent assortment - there are various combinations of ways maternal and paternal chromosomes can be distributed between the two daughter cells
what are chromosome mutations
changes to the structure of chromosomes, or changes to their number
changes to the structure include:
- translocation (swapping of genes)
- duplication
- deletion
- inversion
what are the results of a different number of chromosomes
- aneuploidy happens as a result of non-disjunction. this is where homologous chromosomes or sister chromatids fail to separate
this results in either….
1. more than 2 chromosomes in a pair(polysomy). eg downs syndrome
2. less than 2 chromosomes a pair (monosomy) eg turners syndrome
explain meiosis
- the DNA replicates so there are two identical copies of each chromosome, called chromatids
- the DNA condenses to form double armed chromosomes, made from two sister chromatids.
- chromosomes arrange themselves into homologous pairs
- first division (meiosis 1): homologous pairs are separated, halving chromosome numbers
- second division(meiosis 2): pairs of sister chromatids are separated
- four new daughter cells that are genetically different produced
what is a locus
the position of a gene on a chromosome
what does it mean to say some genes are linked
- genes with loci on the same chromosome
- as they are on the same chromosome, they stay together during independent assortment and their alleles will be passed on to the offspring together
- the closer together the loci of two genes, the more closely they are linked. this is as crossing over is less likely to split them up
differences between eukaryotic and prokaryotic cells
- prokaryotic cells are smaller
- smaller ribosomes (70s) compared with eukaryotic cells (80s)
- prokaryotic cells have no nucleus, but instead a single circular bacterial chromosome
- prokaryotic cells have no membrane-bound organelles
magnification formula
image size / actual size
what is the significance of mitosis
- growth:
- The two daughter cells produced are genetically identical to one another (clones)
and have the same number of chromosomes as the parent cell
This enables unicellular zygotes (as the zygote divides by mitosis) to grow into
multicellular organisms - replacement of cells and repair of tissues:
- cells can be continually replaced by genetically identical cells - asexual reproduction:
- offspring are genetically identical to the parent
explain the process of crossing over
process:
1. During meiosis I homologous chromosomes pair up and are in very close proximity to each other
2. The paired chromosomes are known as bivalents
3. The non-sister chromatids can cross over and get entangled
4. These crossing points are called chiasmata
5. The entanglement places stress on the DNA molecules
6. As a result of this, a section of chromatid from one chromosome may break
and rejoin with the chromatid from the other chromosome
explain independent assortment
Independent assortment is the production of different combinations of alleles in daughter cells due to the random alignment of homologous pairs along the equator of the spindle during meiosis I
1.In meiosis I, homologous chromosomes pair up and are pulled towards the equator of the spindle
2. Each pair can be arranged with either chromosome on top, this is completely
random
3. The orientation of one homologous pair is independent/unaffected by the
orientation of any other pair
4. The homologous chromosomes are then separated and pulled apart to different
poles
bacterial dna is….
circular with no nuclear membrane
how is DNA organised in a bacterial cell
- large circular DNA
- not associated with any histone proteins
- small plasmids
- located in the cytoplasm
describe what happens to lysosomes once their contents have been digested
- lysosome fuses with the cell membrane
- contents of lysosome released from the cell via exocytosis
where is RNA found
- cytoplasm
- nucleus
- mitochondria
why is the nucleolus not found in prokaryotic cells
- do not have a nucleus
why the nucleus cannot be observed at the end of prophase in a eukaryotic cell
- nuclear membrane breaks down
- DNA is coiled into individual chromosomes
explain the PURPOSES of each stage of drug testing
1st stage : to make sure drug is not harmful
2nd stage: to see if it is effective
3rd stage: to gather data for statistical tests and look for rare side effects
how is a polypeptide processed after translation
- moves through endoplasmic reticulum then the golgi appartus
- in the RER, the polypeptide is folded
- in the golgi the carbohydrate is added
- the polypeptide is then transported around the cell in a vesicle
where does protein synthesis occur in a eukaryotic cell
80s ribosomes on the endoplasmic reticulum
why is a line of best fit inaccurate when calculating results
- variation about the line
- the gradient of the line may not remain the same
Explain why the following techniques are used when producing a root tip squash to observe
cell division
1. adding HCl to the root tip
2. adding a stain to the root tip
- breaks down middle lamella, allowing cells to be separated to allow light to pass through
- makes the chromosomes visible so that the stages of mitosis can be identified
explain why offspring may be genetically different even though they are from the same father and mother
- each zygote is formed from different gametes
- each gamete contains different combination of alleles
- different combination of alleles due to crossing over and independent assortment during meiosis
explain ‘sex linked’ disorder
- disorder caused by a mutated gene
- located on the x or y chromosome
- therefore the disorder is more likely in one gedner than the other
why can hardy weinburg not be used for male sex linked disorders
- males only have one allele for the gene
- cannot be heterozygous
- hardy weinburg equation assumes all individuals have two alleles for the gene
explain why some genes show linkage and others show sex linkage
- there are more genes than there are chromosomes
- linkage relates to genes located on the same chromosome
- sex linkage relates to genes on the sex chromosome
what is the fertilised cell in humans described as
diploid zygote
how may crossing over differ in sex chromosomes
- chromosomes cannot form between the x and y chromosome
- because they are not homologous chromosomes
why is dna replicated before mitosis begins
- to ensure that there is one copy of each chromosome in each daughter cell
- to ensure daughter cells are genetically identical
Explain how large numbers of cells with the same phenotype can be produced in a
tissue
- phenotype is determined by the genotype and the effect of the environment
- mitosis produces cells with the same genotype
Describe how each gamete receives only one allele of each gene
- in meiosis homologous chromosomes are separated from one another
- sister chromatids are also separated from one another
- spindle fibres pull chromosomes to opposite poles of the cell
polygenic definition
- a characteristic showing continuous variation
- caused by multiple genes at different loci
how do genes become specialised
signals cause some genes to be switched on
only active genes are transcribed to produce mrna
mrna leads to synthesis of specific proteins which cause cell modification
why can stem cells from the heart not be used to repair the cornea
- cells are not totipotent
- therefore some genes have already been activated and deactivated
- thus, will not be able to specialise into cornea cells
why is a nucleolus not found in prokaryotic cells
they do not have a nucleus
two functions of golgi
forms vesicles
modifies proteins
what is the purpose of each phase of drug testing
phase 1 - make sure drug not harmful
phase 2 - to see if effective at treating condition
phase 3 - to gather data
Explain how preventing the shortening of spindle fibres affects mitosis
sister chromatids cannot be separated
mitosis stops at metaphase
daughter cells produced with the incorrect numbers of chromosomes
Explain how vesicles are involved in the successful fertilisation of an egg cell by only one
sperm.
- cortical granules fuse with the egg cell surface membrane
- releasing enzyme that hardens zona pellucida
cm to mm
mm to micrometres
micrometres to nanometres
x10
x1000
x1000
After the sperm cell nucleus fuses with the egg cell nucleus, the single fertilised cell is
described as a
diploid zygote
Explain how crossing over may differ in sex chromosomes.
crossovers cannot form between some sections of the x and y chromosomes
because they are not homologous chromosomes
Explain why DNA is replicated before mitosis begins.
- to ensure one copy of each chromosome in each daughter cell
- to ensure daughter cells are genetically identical
Explain how large numbers of cells with the same phenotype can be produced in a
tissue.
- phenotype is determined by the genotype and the effect of the environment
- mitosis produces cells with the same genotype
Describe how each gamete receives only one allele of each gene.
- in meiosis homologous chromosomes are separated from one another
- sister chromatids are also separated from one another
- spindle fibres pull chromosomes to opposite poles of the cell
Describe how the acrosome is involved in the digestion of the zona pellucida.
- membrane of the acrosome fuses with the plasma membrane
- releasing enzymes
- by exocytosis
Give a reason for the high density of mitochondria found in the midpiece of a sperm cell.
energy/atp for movement of flagellum
Following fertilisation a zygote is formed.
The zygote then divides by…
mitosis to produce diploid cells
Cell division during the production of gametes produces genetic variation.
This type of cell division involves…
two divisions to produce haploid cells
compare and contrast mitosis and meisosis
both increase number of cells
mitosis produces diploid cells, meiosis produces haploid cells
meiosis produces cells that are genetically different
mitosis results in 2 daughter cells, meiosis produces 4
Explain why an individual may have a greater adult height than their biological parents.
height is affected by the environment as well as the genotype
eg height affected by nutrient intake
height is an example of polygenic inheritance
offspring can inherit a mixture of alleles from both parents
molecular phylogeny definition
molecular differences/similarities in DNA in proteins
compare and contrast acrosome and cortical reaction
- both involve vesicles
- both involve release of chemicals by exocytosis
-acrosome reaction causes digestion of zona pellucida, cortical reaction causes hardening of zona pellucida
