B3a - molecules of life Flashcards
Why do liver and muscle cells have large numbers of mitochondria?(4)
Number of mitochondria in the cytoplasm depends on the activity of the cell, since respiration occurs in the mitochondria
Liver and muscle cells need a lot of energy so they need a large number of mitochondria
- Liver cells carry out energy demanding reactions
- Muscle cells need energy to contract
Describe ribosomes(3)
Some structures in a cell are too small to be seen with a light microscope - e.g. ribosomes
Also found in the cytoplasm
Site of protein synthesis
Describe the structure of DNA(3)
Two strands coiled to form a double helix
Each strand containing chemicals called bases, of which there are four different types
Cross links between the strands formed by pairs of bases.
Describe chromosomes(2)
Long, coiled molecules of DNA
Divided up into regions called genes.
Describe genes(3)
A section of chromosome made of DNA
Each gene contains a different sequence of bases
Each gene codes for a particular protein
What are the 4 bases
A,T,C,G
Describe complementary base pairing(2)
A pairs with T
G pairs with C
How is protein structure determined by the DNA base code(2)
The base sequence determines amino acid sequence
Each amino acid is coded for by a sequence of 3 bases.
Why is a copy of a gene needed to make proteins(4)
Proteins are made in the cytoplasm by ribosomes
Genes cannot leave the nucleus as they are too big to fit through the gap
A copy of a gene is used which can leave the nucleus and carry the code needed to make the protein to the cytoplasm
-done by mRNA, which carries the code from the DNA to the ribosomes
How does DNA control cell functions
By controlling the production of proteins, some of which are enzymes
What data did Watson and Crick use from other
scientists to build a model of DNA(2)
X-ray data showing that there were two chains wound in a helix
Data indicating that the bases occurred in pairs
Why are new discoveries, such as Watson and
Crick’s, not accepted or rewarded immediately
Other scientists need to repeat and test the work to make sure it is correct
