Topic 3 Voice of the genome Flashcards
Describe how DNA is organised in a bacterial cell. (3)
-DNA is circular.
-DNA not associated with histone proteins.
-Several plasmids.
-Located in cytoplasm/no nucleus.
What’s the differences between eukaryotic and prokaryotic cells? (4)
-Eukaryotic cells have membrane bound organelles.
-Eukaryotic cells contains RER.
-Eukaryotic cells have 80s ribosomes whereas prokaryotic cells have 70s ribosomes.
-Eukaryotic cells have linear DNA.
-Eukaryotes don’t have plasmids.
Describe features that could be used to identify prokaryotic cells in blood sample. (4)
-Presence of cell wall.
-Circular DNA/plasmids.
-70s ribosomes.
-Pilli/flagellum.
-Capsule/mesosome.
Explain why the nucleus cant be seen at the end of prophase. (2)
-As nuclear membrane is broken down.
-As DNA is condensed into individual chromosomes.
Describe how a polypeptide is processed to produce a protein. (4)
-The polypeptide chain moves through the endoplasmic reticulum then the Golgi apparatus.
-In the RER the polypeptide is folded.
-In the Golgi apparatus a carbohydrate is added.
-The protein is then transported around cell in vesicle.
Explain why interferon made by genetically modified bacteria is different from interferon made by animal cells. (3)
-Bacteria doesn’t have an RER.
-Meaning polypeptide chain isn’t modified properly.
-Therefore protein is incorrectly folded.
Describe what happens in an acrosome reaction. (1)
-Sperm cell releases digestive enzymes that digest zona pellucida.
Devise an investigation to determine the effect of exposure time to Agil on the rate of mitosis in onion root tips. (6)
-Controlled concentration of agil used.
-Temp/age of onion kept same.
-Roots exposed to agil for a range of time intervals.
-HCl used to make cells more visible, macerate.
-Toluidine blue stain used to make chromosomes more visible then squash down with a cover slip.
-Observe under microscope and count no. cells undergoing mitosis and total no. cells and calculate mitotic index.
Explain why HCl is added to root tip in mitosis CPAC. (2)
-Breaks down middle lamella.
-Allowing cells to be separated.
-So light can pass through more easily.
Explain why a stain is added to root tip in mitosis CPAC. (2)
-Makes chromosomes more visible.
-So stages of mitosis can be identified.
Explain how preventing shortening of spindle fibres affects mitosis. (2)
-Sister chromatids can’t be separated.
-Mitosis stops at metaphase.
-Daughter cells produced with incorrect no. chromosomes.
Describe the events of fertilisations that occurs after the acrosome reaction. (3)
-Sperm cell fuses with egg cell membrane.
-Cortical granules release contents into zona pellucida.
-Contents of cortical granules cause zona pellucida to harden once they react with one another.
-Sperm and egg cells haploid nuclei fuse.
Explain why twins may be genetically different although they have the same parents. (2)
-Each zygote is formed from different gametes.
-Each gamete contains different combinations of alleles.
-Different combinations of alleles due to independent assortment and crossing over during meiosis.
Once a egg cell has been fertilised by a sperm cell explain why a second sperm cell can’t fertilise the same egg cell. (3)
-Cortical reaction occurs meaning cortical granules fuse with egg cell membrane.
-Causing the zona pellucida to harden.
-Therefore other sperm cells can’t reach egg cells membrane.
Explain what is meant by the term sex linked disorder. (2)
-It is a disorder caused by a mutated allele.
-Located on sex chromosomes (X/Y).
-So disorder is more likely linked in one gender than the other.
Explain why a sperm cell with 2 flagella may reduce fertility. (3)
-Presence of 2 flagella affects ability of sperm to propel itself.
-May prevent sperm from reaching egg.
-Preventing fertilisation.
Describe how meiosis leads to genetic variation in gametes produced. (2)
-Non identical gametes produced due to independent assortment of chromosomes.
-Crossing over between non sister chromatids of homologous chromosomes.
Explain why some genes show linkage and others show sex linkage. (3)
-There are more genes than there are chromosomes.
-Linkage relates to genes for different characteristics located in same non sex chromosomes.
-Sex linkage relates to genes on sex (X/Y) chromosomes.
Explain how crossing over may differ in sex chromosomes. (2)
-Crossovers can’t form between some sections of X and Y chromosomes.
-As they aren’t homologous chromosomes.
What is a homologous pair?
2 Chromosomes with exactly the same genes but different alleles, maternal and paternal.
Explain why is DNA replicated before mitosis begins. (2)
-To ensure there’s one copy of each chromosome in each daughter cell.
-To ensure daughter cells are genetically identical.
Name the part of a chromosome that is occupied by a gene. (1)
-Locus.
Describe what happens during prophase in an animal cell. (3)
-Nucleus/nuclear envelope breaks down.
-Spindle fibres formed.
-Chromosomes condense.
-Centrioles migrate to opposite poles/ends of the cell.
Why is there a high density of mitochondria in the midpiece of a sperm cell? (1)
-Provides energy for movement of the flagellum.
Explain why genes found on sex chromosome pair have a pattern of inheritance that is different from genes found on other chromosome pairs. (2)
-X chromosome carries genes that aren’t present on Y chromosome.
-Males have only one copy of some genes.
-If only one allele inherited it will be expressed.
Describe the appearance of chromosomes in cells undergoing metaphase. (2)
-Chromosomes are condensed.
-They are joined to spindle fibres.
-The chromosomes are aligned on the equator of the cell.
What does polygenic mean? (2)
-A characteristic showing continuous variation.
-Caused by multiple genes at different loci.
What is continuous variation?
Variation within a range, includes mass and height.
What is discontinuous variation?
Can only take particular values such as gender or shoe size.
Explain how epigenetic changes affect development of tissues in embryos. (3)
-DNA is wrapped around histones.
-Acetylation/modification of histone affects binding of RNA polymerase.
-Methylation of DNA affects transcription of genes.
-Therefore gene expression is altered.
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Give a difference between a tissue and an organ. (1)
-A tissue is made of one type of cell and an organ is made of different tissues.
Describe the decisions society has to make about the use of embryonic stem cells. (3)
-Embryonic stem cells are totipotent and can be used in a wider range of therapies than other stem cells.
-Source of embryonic stem cells has to be regulated.
-Ethical issues surrounding the embryos being destroyed by using embryonic stem cells.
-Need for research establishments to be regulated/licensed.
Give the meaning of the term totipotent cell. (2)
-A cell that has the ability to differentiate.
-Into all types of cells.
Describe how embryonic stem cells can be specialised to form tissues and organs. (3)
-Chemical signals/activators and repressors cause some genes to be switched on or off.
-The genes that are activated/switched on are transcribed and produce mRNA.
-mRNA leads to synthesis of specific proteins which cause cell modification.
Explain why stem cells from the heart can’t be used to grow cells to repair the cornea. (3)
-Stem cells from the heart are not totipotent.
-Therefore some genes have already been activated and deactivated.
-Therefore will not be able to specialise into cornea cells.
Explain why chemicals from the eye are needed to produce corneal cells from stem cells. (4)
-Chemicals cause some genes to be switched on or off.
-The genes that are switched on are transcribed producing specific mRNA.
-Specific mRNA is translated into specific protein.
-These proteins cause the cell to develop into a corneal cell.
Deduce why age affects time taken to recover from injuries. (3)
-As age increases, time taken to recover from injury increases.
-Due to fewer stem cells in bone marrow with age.
-Fewer stem cells to replace cells in bone/muscle/cartilage tissues.
What is a stem cell? (2)
-A cell that is undifferentiated.
-That can give rise to specialised cells.
-That can divide to produce more stem cells.
Compare and contrast the results of mitosis and meiosis in production of sperm and stem cells. (4)
-They both increase the number of cells.
-Mitosis produces diploid cells and meiosis produces haploid cells.
-Mitosis produces cells that are genetically identical , whereas meiosis produces cells that are genetically different.
-Mitosis results in 2 daughter cells whereas meiosis results in 4 daughter cells.
Epigenetic changes can cause monozygotic twins to have different body masses.
Explain how epigenetic changes can cause differences in a characteristic. (3)
-DNA methylation/histone modification.
-Causes genes to be switched on or off/activated or deactivated.
-Affecting enzyme production.
Explain how epigenetic changes affect activation of genes in daughter cells. (3)
-Genes switched on or off in stem cells.
-Due to DNA methylation.
-Therefore same genes will be activated in daughter cells.
Explain why an individual may have a greater adult height than their biological parents. (4)
-Height is affected by environment as well as genotype.
-Height is an example of polygenic inheritance.
-Therefore offspring can inherit a mixture of alleles from both parents.
-Diet can also influence height, high calcium or protein diet can increase height.
Describe how stem cells can give rise to different types of cells. (4)
-Different stimuli activate/switch on different genes.
-The activated genes are transcribed to produce mRNA.
-mRNA then translated to produce a protein.
-Protein determines function of cell.
-Different proteins produced from different activated genes produce different types cells.
Describe what is meant by the term operon. (2)
-A section of DNA.
-Controlled by a single operator/promotor.
Describe the effect of lactose on the lac operon. (3)
-When lactose is present it binds to the repressor.
-This changes the repressors shape, now it can’t bind to the operator site.
-This allows RNA polymerase to now carry out transcription.
