Cells Flashcards
RNA
Cell wall
Enzyme molecule
Capsid
Which of the above features belong to a HIV particle and which belong to a bacterium?
RNA- HIV and bacterium
Cell wall- bacterium
Enzyme molecules- HIV and bacterium
Capsid- HIV
Describe how a complementary strand of HIV DNA is made
Free nucleotides bond through complementary base pairing (A to T and C to G). DNA polymerase then comes and forms phosphodiester bonds between phosphates and hexose sugars through a series of condensation reactions
Contrast the structures of DNA and mRNA molecules to give all the differences
Uracil replaces thymine in RNA
DNA contains deoxyribose sugars whereas mRNA contains ribose sugars
mRNA is single stranded whereas DNA is double stranded
DNA is long whereas RNA is short
DNA has base pairing (hydrogen bonding) whereas mRNA doesn’t
DNA has introns whereas mRNA doesn’t
How does a HPV vaccine lead to the production of an antibody against HPV
The vaccine will introduce and dead or weak strain of HPV into the body. These will be displayed on an antigen presenting cell (such as phagocytes) from primary response. A specific T helper cell will detect the antigen and stimulates a specific B cell to divide and form clones to give plasma cells. B cells produce antibodies.
Cholesterol increases the stability of plasma membranes. Cholesterol does this by making membranes less flexible.
Suggest one advantage of the different percentage of cholesterol in red blood cells compared with cells lining the ileum.
Red Blood Cells are free in the blood and its structure is not supported by other cells. Cholesterol maintains its shape.
E. coli has no cholesterol in its cell-surface membrane. Despite this, the cell maintains a constant shape. Explain why.
E-coli has a murein cell wall that is strong and rigid and maintains its shape.
Describe how you would test a piece of food for the presence of lipid.
- Dissolve in alcohol, then add water;
2. White emulsion shows presence of lipid.
Human papilloma virus (HPV) is the main cause of cervical cancer. A vaccine has been developed to protect girls and women from HPV.
Describe how giving this vaccine leads to production of antibody against HPV
The vaccine introduces a weak or dead strain of the HPV virus. T-helper cells with specific receptors complementary to HPV antigens will bind to antigen presenting cells, stimulating specific B-cells. A B-cell detects the antigen and then divides by mitosis to form plasma cells. These plasma cells produce antibodies.
There is genetic diversity within HPV.
Give two ways doctors could use base sequences to compare different types of HPV.
Compare the base sequences of DNA and look for mutations or look at mRNA.
HIV attaches to a specific protein receptor on helper T cells. A low percentage of people have a mutation of the CCR5 gene which codes for this protein receptor. This mutation results in a non-functional protein receptor.
Explain how this mutation can result in the production of a non-functional protein receptor.
A mutation changes the DNA base sequence. This changes the amino acid sequence. This alters the hydrogen/ionic and disulphide bonds that are formed meaning the tertiary structure will have changed and so it will no longer be complementary to HIV
People with the CCR5 mutation show a greater resistance to developing AIDS.
Explain why.
They will not have a complementary receptor to the HIV so their T-helper cells cannot be destroyed.
The frequency of the CCR5 mutation is highest in Europe. Scientists have collected data on the history and number of HIV infections in Europe. Using these data, scientists have concluded that the high frequency of the CCR5 mutation is not due to natural selection in response to HIV.
Suggest two reasons why scientists reached this conclusion.
HIV is a relatively new disease and natural selection takes many generations to develop.
Europe has had a lower exposure to HIV.
The mutation has been around for many years and may be advantageous for something else.
Contrast the processes of facilitated diffusion and active transport.
Facilitated diffusion does not require ATP, it is a passive process, whereas active transport cannot function without it.
Facilitated diffusion transports molecules down its concentration gradient whereas active transport moves molecules against their concentration gradient. They both use carrier protiens but facilitated diffusion involves channel proteins too.
