Class Notes of DNA and Proteins Flashcards
What are the large molecules in living organisms called?
macromolecules
What is the main role of DNA in cell?
It is the long term storage of information
What is the function of DNA?
It contains the instruction to construct other components of the cell such as proteins and RNA molecules.
What is genes?
DNA segments that carry genetic information
Where is the DNA stored in eukaryotes (animals and plants)?
Inside the cell nucleus
Where is the DNA stored in the prokaryotes(bacteria)?
In the cells’ cytoplasm
What is the structure of DNA?
- Double helix structure consisting of two strands coiled like a spring
- DNA is composed of repeating units called nucleotides
- A nucleotides consists of sugar molecule, a phosphate group and a nitrogenous base
- Chains of nucleotides form the sugar-phosphate backbone
- there are 4 bases (adenine (A), thymine(T), guanine(G) and cytosine (C)
- adenine always form weak hydrogen bonds with thymine on the adjacent DNA strand of the double helix(A-T).
- Guanine always form weak hydrogen bonds with cytosine(G-C)
- hydrogen bonds are weak so they can break and reform easily when DNA is replicated
- There is always the same amount of thymine and adenine as there they are pairs.
What is X-ray crystallography?
- a piece of evidence that was useful in deducing the double-helical structure of DNA
- used to determine the atomic and molecular structure of a crystal.
- crystalline atoms cause a beam of incident X-rays to diffract onto many specific directions.
- by measuring the angles and intensities of these diffracted beams, produce the picture of a three-dimensional picture of the density of electrons within the crystal form which the average position of the atoms in the crystal can be determined as well as their chemical bonds.
What are genes?
a segment of the DNA molecule (i.e a sequence of bases ) that code for the production of protein molecules, a part of protein molecules (a polypeptide) or an RNA molecule
What does genes determine?
determine what proteins are made within cell therefore determine the structure and function of the cell.
What is a chromosome?
single DNA molecule and its associated histone proteins
Does each organism have the same number of chromosomes in each somatic cell (non-sex cells)
yes
Is the number and type of chromosomes in the somatic cells of an organism unique for each species
Is the number and type of chromosomes in the somatic cells of an organism unique for each species
What is needed for the cell to multiply?
for cells to multiply, the DNA has to be replicated so that each cell receives a complete copy of all chromosomes
When is a chromosome visible?
only visible just after the DNA has been copied and the 2 copies ( called sister chromatids) are still attached. the DNA is highly condensed and so becomes visible. it appears as an X-shaped joined at the centromere.
What is a karyogram?
Karyogram is photograph taken when the DNA is condensed and visible. these photos can be cut out and arranged in order of size, numbered and pasted.
Why is the karayotype of each specie unique?
it is unique as chromosmes vary in sizes and numbers between species . female xx and male xy.
Where are genes located on a chromosome?
they are located in specific positions on a chromosome. these positions are called the gene’s locus or gene loci.
How do the gene locus vary?
- gene present
- length
- banding pattern
How does prokaryotic cell differ from a eukaryotic cell
prokaryotic cells are much smaller and have no nucleus and lack membrane bound organelles.
What is the shape of the chromosome in a prokaryotic cell
It is a single circular chromosome. may also have smaller pieces of circular DNA called plasmids.
Describe the chromosome in eukaryotic cells?
Multiple rod-shaped chromosomes and two copies of their genetic material( on homologous chromosomes).
Where is the chromosome in a prokaryotic cell found?
found in a part of the cytoplasm called a nucleoid. the chromosome is surrounded by a semi-liquid fluid called cytosol mainly consisting of water, but also some organic and inorganic molecules.
What are the similarities between the DNA of mitochondria and chloroplasts and the DNA of bacteria?
They provide evidence supporting the theory of endosymbiosis . this theory suggests that mitochondria and chloroplasts originated as free living prokaryotic cells
What is DNA replication?
DNA is the process of copying chromosomes.
What is genetic code and where is it stored?
it is a sequence of bases on DNA that make up a code of instructions. it is stored in the nucleus of cells.
What does the genetic code provide
provides the information needed to instruct the cell to carry out its functions.
What are the steps involved in DNA replication
- the complementary strands of the double helix are unwounded by helicase. helicase breaks the hydrogen bonds between complementary bases. The bases are exposed.
- Free nucleotides pair with the exposed bases in a complementary way i.e A-T and G-C
- DNA polymerase join the nucleotides together to form 2 new strands of nucleotides which are complementary to the original strands.
- DNA polymerase checks that the new sequence is complementary to the original sequence. it removes and replaces misplaced nucleotides.
- the complementary strands of DNA then wind into 2 double helices.
What is the process of DNA replication known as
Semi-conservative replication
What does it mean by semi-conservative replication
Each double helix consists of one ‘new’ or newly synthesised and one ‘old’ or original strand of DNA. the ensures accuracy in the process of reproducing the gene.
What are the two types of sequences in a gene
introns and exons