Toothpaste Kisses

Enzymes and the ‘lock and key’ theory

Key ideas about enzymes

• Made of protein
• Biological catalyst (speeds up reactions)
• Used for all the chemical changes in the cell e.g respiration and digestion.

Lock and key theory

Enzymes are a particular shape and join together with the substrate, just like a lock and key.

The substrate locking into the active site causes a reaction to make them break down and leave the enzyme molecule.

The higher the temperature, the faster the moecules move which causes more collisions to take place, leading in to more reactions and faster breaking down. 

Above 50 degrees, proteins start to denature, this is  because they’re moving too quick causing a lot of unsuccessful collisions to happen. Therefore, the protein changes shape. This then leads to the rate of movement decreasing  and stop working.

Cells and DNA

• A cell has a nucleus, cell membrane and cytoplasm containing mitochondria
• Chromosomes in the nucleus carry coded information in the form of genes made from DNA. A person’s DNA is unique
• DNA is found in pieces called chromosomes, we have 46 chromosomes and 23 pairs.
• DNA is a double helix with cross links of two bases
• DNA controls protein synthesis (which can be enzymes) Each gene codes for a protein
• DNA has four bases. A-T and G-C are complementary base pairs
• DNA replicates by unzipping and rebuilding by base pairings
• The base sequence determines the amino acid sequence and the protein produced
• Three bases code for one amino acid
• Amino acids are used to build proteins, like enzymes. 
• Enzymes do all the main jobs in the cell. If the DNA code is wrong, the enzyme is built with the wrong amino acids and therefore won’t work.
• A mutation is a chance in the DNA.

Plant hormones

• Plant hormones (auxins) control plant growth, flowering and fruit ripening
• Plant hormones are carried in solution
• Phototropism is a plant’s response to light
• Geotropism is a plant’s response to gravity
• Shoots are positively phototropic (grow towards light) and roots are negatively phtotropic (grow away from light)
• Shoots are negatively geotropic (grow away from the effect of gravity) and roos are positively geotropic (grow towards gravity)
• P;lant hormones are used in selective weed killers, rooting powder, fruit-ripening sprays and seed germination
• Plant tips makes auxins
• The unequal distribution of auxins in a shoot causes it to grow towards light 

Cells and growth

• A plant cell is different from an animal cell since it has chloroplasts, a cell wall and large vacuoles
• Plant cells are supported by the cellulose cell wall and pressure from the cell snap in the vacuole
• Growth in plants and animals needs cell division and cell differentiation (specialised cells)
• Unspecialised cells are called stem cells
• Plants grow continuously but animals stop growing at maturity
• Plant cell growth is different from that in animals because it relies more on cell enlargement, cell division is mainly in the tips and most cells are capable of differentiation

Vacuole- Contains cell snap and provides support

Cell wall- Providessupport

Chloroplast- Absorbs light energy for photosynthesis

Meiosis and reproduction

• In sexual reproduction, a female gamete is fertilised by a male gamete
• Many sperm are made to ensure fertilisation
• Sperm have many mitochondria (to release energy) and an acrosome with enzymes to dissolve the egg membrane
• The egg is larger than the sperm since it has much more food
• The gametes are made by a cell division called meiosis
• Each gamete only has a half set of chromosomes ; this is called haploid
• Since chromosomes and genes are mixed up in meiosism the process results in variation
• In meiosis, pairs of chromosomes seperate to go to opposite ends of the cell
• A second division takes place when the chromosomes divide
  

Mitosis

• Cells divide so the organism can grow and replace or repair damaged cells
• This type of cell division is called Mitosis
• Mitosis makes identical new cells containing the diploid number of chromosomes
• Multi-cellular organisms can be large and complex with different cells
• Being multi-cellular is better than having one large cell because it will have a better surface area to volume ratio
• In mitosis, the chromosomes are copied to produce genetically identical cells.
• In mitosis, the chromosomes divide and go to opposite ends of  the cell

Ok so this was meant to be a ‘private’ account or whatever but I never use it so I’m going to use it as a revision blog filled with notes and whatever, mainly for science as it’s the only exam I have left except maths but that’s a while away.