Slides in this set

Slide 1

Preview of page 1

Growth and
B5 OCR 21st Century
Additional Science…read more

Slide 2

Preview of page 2

Structure of DNA
A DNA molecule has two strands coiled together in the
shape of a double helix.
DNA is made up of nucleotides ­ a nucleotide contains: a
base, sugar and phosphate.
There are four bases and two base pairings:
Adenine (A) pairs with Cytosine (C)
Guanine (G) pairs with Thymine (T)
The bases pair together with hydrogen bonds
Adenine and Cytosine have two hydrogen bonds.
Guanine and Thymine have three.
Adenine and Thymine won't be able to pair together
because they have a different amount of bonds.…read more

Slide 3

Preview of page 3

Amino Acids & Proteins
A gene is a section of DNA that contains the
instructions for making one protein.
Proteins are made by amino acids being put
together in a certain order ­ it's the order of the
bases that determines the order of the amino
It takes three bases to make on amino acid ­
this is the triplet code.…read more

Slide 4

Preview of page 4

Making Proteins
1. First the DNA unzips so the strands become
separate and the base pairs separate. A
molecule of RNA (a special type of DNA) moves
in and creates a pair with the bases on the
DNA. The only difference is that there is no
Thymine, instead there is (U). This is
2. The RNA then moves out of the nucleus and
then goes into the cytoplasm. A ribosome then
joins on and moves along the RNA chain to join
amino acids together to make proteins using
the triplet code. This is translation.…read more

Slide 5

Preview of page 5

Mitosis is when cells divide to duplicate themselves.
1. First, the cell duplicates everything in the nucleus so
there are twice the number of chromosomes and that
there are two copies of DNA.
2. Then the DNA forms X-Shaped chromosomes that line
up at the centre of the cell and then go to opposite sides
of the cell.
3. Membranes form around the chromosomes ­ this
becomes the nucleus.
4. The cytoplasm divides.
5. There are now two cells with exactly the same DNA.…read more

Slide 6

Preview of page 6

Meiosis happens in gametes, cells that have half the
number of chromosomes (egg & sperm cells).
1. The amount of chromosomes duplicate and then
line up in the centre. They are then pulled apart so
that during the first division, there is only one copy
of each chromosome in each cell.
2. Then after the first division has taken place, the
chromosomes line up again in both of the cells.
They arms of the x-shaped chromosomes are then
split apart and then the cells divide again so that
there are four cells with only one set of
chromosomes.…read more

Slide 7

Preview of page 7
Preview of page 7

Slide 8

Preview of page 8
Preview of page 8

Slide 9

Preview of page 9
Preview of page 9

Slide 10

Preview of page 10
Preview of page 10




thanks very helpful

Similar Science resources:

See all Science resources »