Cells Flashcards
(24 cards)
What are the purposes of mitosis
For growth and repair
For asexual reproduction
To produce 2 genetically identical daughter cells
Describe the first stage of mitosis
- Prophase - chromosomes condense and become visible in the nucleus. A pair of centrioles move to either side of the cell and spindle fibres form from them. Nucleolus disappears and nuclear envelope breaks down leaving the chromosomes free in the cytoplasm.
Describe the second stage of mitosis.
Metaphase - chromosomes are seen to made up of 2 sister chromatids, joined by a centromere. The chromosomes line themselves up along the middle of the cell.
Describe the third stage of mitosis.
Anaphase - centromeres divide into two and spindle fibres pull the individual chromatids that make up the chromosome to opposite poles of the cell.
Describe the fourth stage of mitosis.
Telophase - the chromosomes reach their respective poles and become longer and thinner, finally disappearing. Spindle fibres disintegrate and nucleolus and nuclear envelope reform. Finally the cytoplasm divides in a process called cytokinesis.
What happens during interphase?
The replication of DNA (chromosomes)
Describe the process of binary fission (prokaryotic cells)
- The single circular DNA molecule undergoes DNA replication
- Any plasmids present undergo DNA replication
- Parent cell divides into two cells, with cytoplasm roughly halved between two daughter cells
- The two daughter cells each contain a single copy of the circular DNA molecule and a variable number of plasmids
Describe simple diffusion
Net movement of molecules from an area of higher concentration to an area of lower concentration. Does not require ATP. Molecules have to be small and soluble.
Describe facilitated diffusion
Passive process (does not require ATP) where carrier proteins and protein channels are used to transport molecules that are polar and are ions or big molecules.
Protein channels form tubes filled with water so water soluble ions can pass through
Carrier proteins bind with a molecule which causes a change in shape of the protein. Shape change enables molecule to be released at the other side.
Describe osmosis
Movement of water from an area of higher water potential to an area of lower water potential across a partially permeable membrane
What does water potential mean?
The pressure created by water molecules. A more negative water potential indicated a more concentrated solution ( more solute dissolved in it)
Define isotonic, hypotonic and hypertonic and how would the water move.
Isotonic solution - when water potential is the same in the solution and in the cell. Water will move in and out
Hypotonic solution - when water potential of the solution is more positive than the cell. Water will move into the cell
Hypertonic - when water potential of the solution is more negative than the cell. Water will leave the cell
Define active transport
Movement of molecules and ions from an area of lower concentration to an area of higher concentration, against the concentration gradient using atp and carrier proteins.
ATP will bind to the protein on the membrane and is hydrolysed to ADP and Pi which releases a small amount of energy
Describe Co transport and the illustration of the absorption of sodium ions and glucose by ileum
The movement of 2 different substances using a carrier protein.
Glucose move down the conc gradient by facilitated diffusion into epithelial cells via carrier proteins
Active transport occurs via a carrier protein called a sodium potassium pump . Using atp the pump actively transports Na ions out of the cell into the bloodstream so there is a low conc on the cell and hight conc outside the cell.
In the membrane there is a sodium glucose transporter as sodium transports through this so does glucose.
Define antigen
Proteins on the cell surface that can be detected by antibodies and trigger an immune response
Define antibody
Proteins produced by the immune system in response to foreign substances. Bind to antigens.
Explain the process of Phagocytosis
- Chemicals are released by the pathogen which attracts the phagocytes
- Phagocytes have receptor binding points on their CS membrane that bind to the antigens on the pathogen
- Phagocyte changes shape to move and engulf the pathogen to form a phagosome vesicle
- Lysosomes move towards the vesicle and fuse with it
- Enzymes called lysozymes are released from the lysosomes and destroy pathogen by hydrolysis
- The products are absorbed into the cytoplasm of the phagocyte
Explain the cell mediated response.
Involves T Cells which mature in the Thymus gland
1. T cell surface receptor binds with complementary antigen only if it’s on the surface of the cell
2. Activates the T-cell to divide by mitosis to from clones
3. These differentiate into :
Memory cells - rapid response to cute infections by the same pathogen. Remain in the bloodstream
Helper T cells - release cytokines which stimulate B cells to develop and divide and stimulate Phagocytosis
Cytotoxic T cells - attack and kill infected body cells making holes in their membrane
Explain the Humoral response
Involves B cells which are activated by T helper cells which mature in the bone marrow
1. Collision of antigen and complementary B cell receptor
2. B cell divides by mitosis to form clone cells
3. Most cloned cells are plasma cells which release antibodies
4. Some are memory cells
Describe and explain the antibody structure
Made from 4 polypeptide chains. 2 long and 2 short joined by disulfide bridges.
Constant region - same in every antibody , uses to bind to phagocytes.
Variable region - unique structure, antigen binding site of antibody - allows antibody to recognise and bind to a particular antigen
Describe how HIV is replicated
Attachment protein attach to receptors on helper T cell
RNA enters the cell
Reverse transcriptase converts RNA to DNA
Viral protein produced
Virus particles assembled and released
Describe the induced fit model of enzyme action
Active site is not complementary to substrate before reaction
Shape of active site changes as substrate binds
Distorting in substrate leads to reaction
Describe how giving a vaccine leads to production of antibody
Vaccine contains antigen from virus
Which are displayed on antigen presenting cells
Specific helper T cell detects antigen and stimulates production of B cells
B cells divide by mitosis and form clones to give plasma cells
Plasma cell produces antibodies
What does Golgi apparatus do in lipid absorption
Modifies/processes triglycerides
Combines triglycerides with proteins
Packages them for release
