Topic 2 & DNA Flashcards
What is a gene?
A section of DNA that codes for a specific protein
What are chromosomes made of?
DNA
Is DNA a polymer?
Yes
What are the monomers of DNA?
Nucleotides (DNA is a polymer made from repeating monomers called nucleotides)
What are the components of a nucleotide?
- phosphate group
- sugar (deoxyribose)
- base
What are the four bases?
Adenine (A)
Cytosine (C)
Guanine (G)
Thymine (T)
How many and what kind of strands are DNA made up of?
Two polymer strands
What is the shape of DNA?
Double helix
How are the polymer strands made into a double helix?
They are twisted
How are bases on one strand linked to those on the other strand?
By weak hydrogen bonds
How are the bases linked? (c- b- p-)
complementary base pairing
What base pairs with what base?
a with t
c with g
How many hydrogen bonds link A and T?
2
How many hydrogen bonds link C and G?
3
What do the sides of the DNA consist of?
A sugar-phosphate backbone
Chromosomes (3 points to make)
- found in nucleus of cells
- made of dna
- in human body cells there are 46
allele
alternative form of a gene
gamete
a sex cell
zygote
fertilised egg cell
what is produced when a sperm fuses with an egg
phenotype
physical/chemical expression of your genotype
genotype
alleles present in the nuclei of your cell
dominant allele
if present, is always expressed in phenotype
recessive allele
only expressed if dominant allele is absent
homozygous
both allleles for a characteristic are the same
heterozygous
the two alleles for a characteristic are different
mitosis
cell division
cancer
uncontrolled cell division
result of dna mutation
can result in tumours forming
benign vs malignant tumour
benign: not cancerous, doesn’t invade other tissues or organs
malignant: cancerous, spread by blood to other tissues/organs and invade them to form secondary tumours
cell cycle of healthy vs cancerous cell
cell cycle of cancerous cell is quicker
how do secondary tumours occur due to metastatis
some of the cancer cells spread to other parts of the body in the blood and invade tissues and organs to form secondary tumours
cell itself normal vs cancerous
normal:
large cytoplasm
single nucleus
single nucleolus
fine chromatin
cancerous:
small cytoplasm
multiple nuclei
multiple/large nucleoli
coarse chromatim
what happens in cytokinesis? (1)
the cytoplasm and cell membrane divides to formtwo separate diploid cells, each of which has genetically identical chromosomes
what happens in telophase? (1)
a nuclear membrane reforms around each new set of chromosomes, separating them
what happens in anaphase (2)
1) spindle fibres contract, splitting chromosomes
2) sister chromatids are pulled to opposite ends of the cell
what happens in metaphase (2)
1) Chromosomes line up at the centre of the cell
2) Spindle fibres attach to chromosomes at the centromere
What happens in prophase? (3)
- DNA condenses and chromosomes become visible
- The nuclear membrane breaks down
- Spindle fibres start to form
What happens in interphase? (3)
Dna is replicated
Normal metabolic processes eg respiration continue to occur
New organelles are made
Stages of cell cycle
Interphase
mitosis
cytokinesis
stages of mitosis
prophase
metaphase
anaphase
telophase
how are proteins made different (a- a-)
different proteins have different sequences of the 20 amino acids
how many bases code for one amino acid
3 (a triplet) on the dna
how many amino acids
20
what are proteins made from
amino acids
genome
entire dna of an organism
why is protease sometimes used instead of detergent and salt in step 1 of dna and fruit
- bc this breaks down proteins in cell membrane
- which breaks down cell membrane
- therefore releases dna
- also destroys enzymes that break down dna
4 steps of core practical extracting dna from fruit
1) grind fruit in detergent and salt (to break open cells by breaking down cell membrane to release dna)
2) filter mixture (to remove debris)
3) pour ice cold ethanol into filtrate (this will precipitate dna as its insoluble in ethanol and so dna can be seen)
4) if desired, remove dna w glass rod
haploid chromosomes
- in sex (haploid) cells there is one of each pair of chromosomes
- so half the number of chromosomes as in a human body cell
chromosomes (3)
- in body cells there are pairs of chromosomes
- cells with two of each pair of chromosomes are said to be diploid
- in humans there are 23 pairs of 46 chromosomes per cell
mitosis vs meiosis 5 points
mitosis:
- produces genetically identical cells
- produces diploid cells
- produces 2 cells
- 1 division
- produces body cells
meiosis:
- produces genetically different cells
- produces haploid cells
- produces 4 cells
- 2 division
- produces sex cells
meiosis produces (2)
- 4 cells, each with half the number of chromosomes as the original cell and one of each pair of chromosomes (haploid)
- cells that are genetically different from each other
where does meiosis occur in humans
women ovaries, men testes
haploid cells
- one of each pair of chromosomes
- so half no of chromosomes
- in humans these are sex cells
- in humans sex cells have 23 chromosomes (one of each pair)
diploid cells
- two sets of chromosomes (full set) in their nuclei
- in humans, body cells have 46 chromosomes/23 pairs
mitosis produces what kinds of cells (4)
- produces 2 cells
- produces genetically identical cells
- produces diploid cells
- produces body cells
importance of mitosis
produces genetically identical cells for: growth, repair and asexual reproduction
examples of plant specialised cells
xylem
phloem
plant stem cells (4)
- can produce all cell types throughout plant’s life
- known as meristem cells
- found in growing regions (meristems) of plants
- they divide by mitosis and differentiation to produce plant specialised cells
adult stem cells
- found in tissues/organs in adult body
- can only differentiate to produce a limited number of cell types
- eg skin cellls in bone marrow can differentiate into different types of blood cell
embryonic stem cells
- found in early embryos
- can differentiate into all cell types
stem cells (4 points)
- undifferentiated cells
- can divide by mitosis and differentiate to produce specialised cells
- can also divide by mitosis to produce new copies of themselves (self-renew)
- only stem cells divide by mitosis
types of animal stem cells
embryonic
adult
stem cell risks
- new cells may not function properly
- if cells are infected w a virus might be transmitted to recipient making them sicker
- stem cells divide very quickly: if transplanted cells also divide quickly a tumour may develop
- if stem cells are not from patient the transplanted cells maybe recognised as foreign and trigger immune response to try and destroy them
stem cells in medicine benefits
- adult stem cells used to treat some diseases
(eg leukemia w/ bone marrow transplant as this contains adult stem cells which produce new blood cells) - also embryonic stem cells are being tested, could replace damaged tissues by disease or injury
(eg replace nerve cells of someone w paralysis in spinal cord)”
ethical issues with extracting stem cells
- could harm embryos by extracting stem cells
- embryos used for cells could be destroyed after leading to loss of a potential human life
tumour
mass of cells
originates from uncontrolled cell division
result of dna mutation
synapse
gap between neurones
synapse passage (5)
1) impulse passes along presynaptic neurone
2) at synapse, the impulse triggers the release of a chemical (neurotransmittor)
3) neurotransmittor diffuses across synapse
4) it binds to receptor sites on post-synaptic neurone
5) this triggers an impulse in post-synaptic neurone
nervous system passage
stimulus
receptor
sensory neurone
impulse
synapse
relay neurone
synapse
motor neurone
effector
response
effector
produces a response
eg a muscle that contracts or a gland that releases a chemical (likely a hormone)
receptor
a group of nerve cells that detects a change in the environment ( a stimulus ) eg pain receptors in skin and light receptors in eyes
relay neurone (2)
found in cns
takes impulse from sensory to motor neurone
motor neurone
takes impulse from cns to effector
sensory neurone
takes impulse from receptor to cns
myelin sheath
fatty substance
acts as an electrical insulator
speeds up movement of electrical impulse
axon
takes impulse from cell body to axon terminals
why don’t relay neurones have a myelin sheath
- unlike sensory and motor neurones, they don’t need to take the nervous impulse a long distance
- only to other neurones in CNS
- so passage of impulse can be slower
dendron
subdivided into dendrites
nervous impulse starts here
dendron takes impulse to cell body
cell body
contains
nucleus
mitochondria
ribosomes
etc
pns meaning
peripheral nervous system
pns components
nerves that lead to and from cns
cns
central nervous system
cns components
brain and spinal cord
point 1 reflex actions
1) stimulus is a change in environment of an organims eg hot flame
point 2 reflex actions
detected by a receptor eg pain receptors in skin
point 3 reflex actions
impulses from a receptor pass along a sensory neurone
point 4 reflex actions
to the spinal cord (co-ordinator)
point 5 reflex actions
the neurotransmittor (chemical) diffuses across synapse between sensory and relay neurone
point 6 reflex actions
then a chemical diffuses across synapse between relay and motor neurone
point 7 reflex actions
motor neurone carries impulse to an effector which is a muscle
point 8 reflex actions
muscle responds by contracting and finger is moved away
reflex arc
passage of impulse from receptor to effector
reflex action example
moving finger away from hot flame
growth
increase in size/mass
what does growth involve in animals?
cell division (mitosis)
cell differentiation
cell differentiation (2)
- carried out by stem cells
- cells become specialised eg change shape eg red blood cell changes shape so it can carry oxygen
in animals when does growth stop
only young animals grow
once adult height has been reached, further growth does not occur
what does growth involve in plants (3)
cell division (mitosis) (meristem cells)
cell differentiation
cell elongation (by absorbing water)
what causes plants to increase in height
cell elongation
do plants ever stop growing?
no
unlike animals they continue to grow throughout their lives
where are meristem cells found
tips of plants shoots & roots
use of percentile growth curves
assess child’s growth over time
so overall pattern of development can be seen
so any problems can be highlighted (obesity, dwarfism, malnutrition)
what measurements are taken for percentile curves
length of baby
mass of baby
baby’s head circumference
what does 50th percentile tell us
mass that 50% of babies will have at a particular age
when will doctors or health professionals investigate in terms of growth percentile curve
if baby’s size is above top or below bottom percentile line
if baby’s size increases/decreases by >2 percentile lines over time
if there are inconsistencies eg small baby large head
what are reflex actions (4)
- involuntary
- protect body
- responses to danger
- do not involve brain as go via spinal cord which speeds them up
